Care & Service Manual

Aircraft tire Care & Service Manual Note : This document, Michelin Reference

#MAT-CSM-01 Rev. A

supercedes Reference #MAT-CSM-95 Rev. B, #MAT-CSM-95 Rev. A, Michelin document MAINT- 0013 and the document entitled Michelin Aircraft Tire Care & Maintenance. Table 3 of contents Introduction 6 Branding 12 is Not Recommended 22 Store Tubes Properly 23 Aircraft Tire Tire serial Tire and Tube Age Limit 23 Construction 7 number codes 17 Storage of Inflated Tire The Tread 8 General Safety and Wheel Assemblies 23 The Undertread 8 Considerations 18 Ozone 24 A Carcass Ply 8 - For Bias Mounting 19 Recommendations for - For Radial Inflating 19 Storage and Handling 25 The Beads 9 Tires In Service 19 - Transportation General Mounting Chafer Strips 9 Instructions The Liner 9 Storing Aircraft For Aircraft Tires 26 The Sidewall 9 Tires And Tubes 20 General 27 Products Unique Handling Aircraft Tires 21 to the Bias Tire 10 Premounting Checklist 27 Avoid Moisture and ozone 21 - Wheels - The Tread Reinforcing Ply - Ozone - What is it ? - Tires - Breaker Plies - Impact of ozone on tires - ORIONTM technology Mounting 29 - Fabric Tread Designing for ozone 21 - Use of Inner Tubes - Spiral Wrap Store away from fuel Bias Tires Products Unique and solvents 22 Radial Tires - Lubrication of Tire Beads to the Radial Tire 11 Store in the Dark 22 Bias Tires - The Protector Ply Store Tires Vertically 22 Radial Tires - Belt Plies Horizontal Stacking of Tires - Tire/Wheel Assembly Chine Tires 11 - Tire/Wheel Alignment Table of contents

- Inflating With Nitrogen the Most Out of Your Tires 39 - Normal Response - Special Procedure Properly Seat - Effects of Underinflation - Testing For Pressure Loss Tube-Type Tires - Effects of Overinflation - Causes of Pressure Loss Basic Pressure Checking Duals for Equal Tire Growth Retention Check 31 Drop in Ambient Temperature Operating Pressure 40 Approved Calibrated Gauge - Procedure Proper Inflation - Setting Foreign Object Damage Emergency Pressure the Pressure Level 41 Improperly Seated Beads Retention Check 32 - Inflating and Reinflating Valve Stem or Valve Core - Procedure the Tire/Wheel Assembly Valve Seal Alternate Pressure - Loaded versus Unloaded Tires Wheel Half Parting Line O-Ring Seal - Properly Inflating Tube - Type Tires Fuse Plug Retention Check 32 Pressure Release Plug - Procedure Effect of ambient temperature Seepage Between Tire Bead and Sidewall Venting 33 on gauge pressure 42 Wheel Flange Not all aircraft tires - Effect of temperature Leakage Through the Well Area - Proper Inflation - Standard are vented 33 Damaged Wheel Sealing Surfaces for Maintaining Pressure Level Damage to the Tire Innerliner Storage of an Inflated Tire - Aircraft experiencing large ambient Cracks or Splits in the Inner Tube and Wheel Assembly 34 temperature differences between - Troubleshooting - airports Have You Considered? Mounting Tire/Wheel Schedule and action 44 Assembly - When to Check Tire Serviceability On The Aircraft 36 Frequency Criteria 51 Checking Hot Tires Visually Inspect Compare tire pressures on the On Aircraft Inspection Tire/Wheel Assembly 37 same given landing gear With Tire Mounted 52 Readjust Tire Pressure 37 Single and Multiple tire gear Removal Criteria - Wear Two Tire Gear Water can affect traction 52 Inflation Pressure Three or more tire gear - Typical Wear Conditions Maintenance 38 - Monitoring Inflation Pressure - Normal Wear What To Do Overinflation Proper Inflation - Getting Pressure Loss 46 Underinflation 5

Worn Beyond Recommended Limits - Observe Load and Retreading Flat Spotting Inflation Recommendations Asymmetrical Wear and Repairing Serviceability Criteria/ Limits Vibration Aircraft Tires 77 For Tire Damages and Balance 70 Retreading Aircraft Tires 78 Tread Wear - Proper inflation pressure Accepting Tires Tread Cuts/ Foreign Objects Inflation is equalized Sidewall Cuts / Foreign Objects Full growth For Retreading 78 Serviceability Criteria/ Beads properly seated Repairing Aircraft Tires 78 Operational Conditions 63 Flat spotting/uneven wear Non-Repairable Aircraft Tires 79 Properly mounted - Hard Landing Repairable Aircraft Tires 79 - Rejected Takeoff Air trapped between tire and tube Off-Aircraft Inspection Tube wrinkled Operating and Wheel out of balance With Tire Dismounted 64 Condition of wheel Handling Tips for - A Systematic Approach to Tire Loose wheel bearing Better Tire Service 80 Inspection Gear alignment Bias tires Worn gear components Taxiing 81 Radial tires Pivoting By Using Brakes 81 General Dismounting Condition of Airport Field 82 Matching Instructions and Mixability For Aircraft Tires 72 Avoid Chemical of Dual Tires 66 Contamination 82 Removal From Landing Gear 73 Matching Tires 67 Nylon Flat Spotting 82 - Matching Criteria Reason for removal- Chevron Cutting 83 Bias Tires Tracking 73 Hydroplaning 83 Radial Tires Tire Dismounting 73 Landings Per Tread 84 New versus Retreaded Tires - Tire/ Wheel Dismounting - Mixability Sequence Bias - Bias Tire Dismounting Equipment 75 Radial - Radial Bias - Radial Introduction

For aircraft tires to deliver The procedures given in this maximum performance, reliability, manual apply to all Michelin durability and safety, they must be manufactured aircraft tires, new or properly cared for and serviced. retreaded, regardless of the family name, current (Michelin Air, This manual is designed as a guide Michelin Air X, Michelin Aviator, to the procedures to be used for all Aviator, BF Goodrich, AAT, aspects of aircraft tire care and Silvertown) or future. The same operation. It provides detailed service and care techniques should information about how to operate be used for both Bias and Radial aircraft tires to achieve optimum tires. In some specific cases, due to service. It also covers installation, the nature of bias and radial tire removal and servicing techniques. constructions, differences in service It should be used in conjunction techniques may exist. Where with the operating procedures given applicable, these differences have by the aircraft and wheel been noted. manufacturers. Whether you operate a single aircraft, or a fleet, the principles and procedures contained in this manual will be of benefit.

If further information is needed, please contact your Michelin Representative.

See back cover for regional contacts. TTireTiire cconstructioncoonnssttrruuccttiion

Aircraft tire 7 construction Aircraft tire construction

An aircraft tire must withstand a wide cross-ply or BIAS tire and the RADIAL The undertread is a layer of range of operational conditions.When tire. Both nomenclatures describe the specially formulated rubber on the ground, it must support the angular direction of the carcass plies. designed to enhance the bonding weight of the aircraft. During taxi, it between the tread must provide a stable, cushioned ride While many of the components of bias reinforcement/protector plies and and radial tires have the same while resisting heat generation, the carcass body. For those tires terminology, the carcass ply angles are abrasion and wear.At take-off, the tire designed to be retreaded, this rubber not the only difference between a bias structure must be able to endure not layer will be of sufficient thickness to only the aircraft load but also the forces constructed tire and a radial constructed tire.The technologies act as the interface for buffing generated at high angular velocities. the old tread assembly, as well as the Landing requires the tire to absorb utilized are quite different involving different design parameters, liaison with the new retread impact shocks while also transmitting products. high dynamic braking loads to the compounds, and materials. ground. All of this must be A carcass ply consists of fabric accomplished while providing a long, The tread refers to the crown area cords sandwiched between two dependable, reliable, service life. of the tire in contact with the ground. Most Michelin tires are designed layers of rubber. Today, the most These extreme demands require a tire with circumferential grooves molded common fabric cord is nylon. which is highly engineered and into the tread area. These provide a The carcass body itself is made from precisely manufactured. mechanism to channel water from multiple layers of carcass plies, each For this reason, tires are designed between the tire and runway surface one adding to the strength and load as a composite of various rubber, which helps to improve ground bearing capability of the tire. fabric and steel products. Each of adhesion. The carcass plies are anchored by the components serves a very specific wrapping them around bead wires, function in the performance The tread compound is formulated thus forming the PLY TURN-UPS. of the tire. to resist wear, abrasion, cutting, FOR BIAS constructed tires, cracking and heat buildup. To meet the aircraft demands of today It prolongs the life of the casing the carcass plies are laid at angles and tomorrow, Michelin designs and by protecting the underlying carcass between 30° and 60° to the centerline produces two different and distinct plies. or direction of rotation of the tire. tire constructions, the conventional Succeeding plies are laid with cord 9 angles opposite to each other, to Depending on the size and design The liner in tubeless tires is a layer provide balanced carcass strength. application, BIAS tires are of rubber specially compounded to constructed with 2 to 6 bead bundles resist the permeation of nitrogen and FOR RADIAL constructed tires, (1 to 3 per side). By contrast, RADIAL moisture through to the carcass. It is each carcass ply is laid at an angle constructed tires have 2 bead vulcanized to the inside of the tire approximately 90° to the centerline bundles (1 on each side) regardless and extends from bead to bead. It or direction of rotation of the tire. of tire size. replaces the inner tube common to Each successive layer is laid at a tube-type tires. similar angle. Radial constructed Chafer strips are strips of protec- All Michelin manufactured Radial tires of the same size have a fewer tive fabric or rubber laid over the aircraft tires are certified for in- number of plies than do tires of a outer carcass plies in the bead area service operation to -55°C. bias construction, because the radial of the tire. Their purpose is to pro- Beginning with manufactured date, cord direction is aligned with the tect the carcass plies from damage June 1999, all Michelin Bias aircraft burst pressure radial force allowing when mounting or demounting and tires are certified for in-service for optimized construction. to reduce the effects of wear and operation to -55°C. chafing between the wheel and the In tube-type tires, a different, thinner The beads or bead wires anchor tire bead. liner material is used to protect the the tire to the wheel. They are carcass plies from moisture and tube fabricated from steel wires layered chafing, but is generally insufficient together and can be embedded with to maintain air retention. rubber to form a bundle. The bundle is then wrapped with rubber coated The sidewall is a layer of rubber fabric for reinforcement. covering the outside of the carcass plies. Its purpose is to protect the cord plies. In addition, the sidewall rubber contains anti-oxidants. They are slowly released over time to protect the tire from ultraviolet and ozone attack, which cause rubber cracking. Aircraft tire tread sidewall tread reinforcing ply construction undertread carcass plies

liner

beads chafer strips carcass ply turn-ups

Bias Tire Construction

10 ORION™ technology

Products unique ORION™ technology is a Fabric tread (not shown) is a to the bias tire development unique to Michelin unique development for application Bias construction. It consists of a on high speed military aircraft. The tread reinforcing ply CROWN REINFORCEMENT placed Multiple plies of nylon cord are consists of single or multiple layers on the inside of the tire. This layered throughout the tread stock, of a special nylon fabric and rubber CROWN REINFORCEMENT reducing rubber distortion under laid midway beneath the tread strengthens and provides a more load and high speeds, thus reducing grooves and top carcass ply. These uniform pressure distribution in the heat normally generated by flexing. plies help to strengthen and stabilize footprint SLOWING THE RATE OF The laminates also control the the crown area, by reducing tread WEAR, improving landings formation of high speed “standing distortion under load, and to performance in a lighter tire design. waves.” Improved resistance to cuts increase high speed stability. They and punctures is also a benefit of also offer a resistance to tread this type of construction. puncture and cutting and help to protect the carcass body. Spiral Wrap (not shown) is a technique used with retreaded tires. Breaker plies (not shown) are Individual textile cords are layed sometimes used to reinforce the within the replacement tread rubber carcass in the tread area of the tire. as it is applied to the tire casing. Cords are oriented to the top 1/2 - 1/3 of the skid and are free to “float.” Because of their circumferential orientation, the textile cords provide added resistance to the cutting and tearing action associated with chevron cutting. tread sidewall protector ply undertread belt plies carcass plies

Single Chine Tire Dual Chine Tire

flipper strip bead liner carcass ply turn-ups

Radial Tire Construction 11

Products unique Chine tires to the radial tire The “chine” tire is a nose wheel tire The chine tire is now in use as The protector ply is typically designed to deflect water and slush standard equipment on many found in retreadable tires to the side and away from intakes on commercial jets. It is fully and placed in the crown area just aft-fuselage mounted jet engines. retreadable and may be used below the tread rubber. It provides on any aircraft provided adequate cut resistance protection to the It consists of a flared upper sidewall clearance is available. underlying belts and carcass plies. protrusion which deflects the spray pattern of water or slush displaced Belt plies are laid between the by the tire’s contact with the runway. tread area and top carcass ply. A tire can have a single chine (one They restrain the outer diameter of sidewall flared) for dual nose wheel the tire, providing a tread surface tire configurations or double chines with greater resistance to squirm (both sidewalls flared) for single and wear as well as providing a more nose wheel tire configurations. uniform pressure distribution in the footprint for improved landings performance. Branding commercial bias tire typical Michelin branding layout

TRADEMARK

PART NO.

TUBELESS OR TUBE- TYPE DESIGNATION

QUALIFICATION STANDARD

12 LOAD RATING MOLDED SKID PLY RATING SPEED RATING

EQUIPMENT IDENTIFICATION

SERIAL NUMBER CODE For details, see page 17 AEA1 CODES COUNTRY OF ORIGIN SIZE DESIGNATION

1. AEA: Association of European Airlines Branding commercial radial tire typical Michelin branding layout

TRADEMARK

MOLDED SKID SERIAL NUMBER CODE For details, see page 17 FAA2 QUALIFICATION STANDARD

DGAC1 QUALIFICATION STANDARD

EQUIPMENT IDENTIFICATION

13 TYPE NUMBER CODE IDENTIFICATION

LOAD RATING PLY RATING

COUNTRY OF ORIGIN

CONSTRUCTION SIZE DESIGNATION DESIGNATION PART NO. SPEED RATING

TUBELESS3 DESIGNATION

1. DGAC: Direction Générale de l’Aviation Civile / 2. FAA: Federal Aviation Administration / 3. All MICHELIN aircraft radials are tubeless Branding military bias tire typical Michelin branding layout

TRADEMARK SERIAL NUMBER CODE For details, see page 17 EQUIPMENT IDENTIFICATION

QTR NO.

CUT LIMITS

MAXIMUM WEAR LIMIT INDICATOR Application is program dependant

14 COUNTRY OF ORIGIN

1 2 SCD NO. OR MS NO. MWL - 3 OR OEM3 SPECIFICATION NO. OR USAF4 NO.

TUBELESS OR TUBE TYPE DESIGNATION

CODE IDENTIFICATION NATIONAL OR NATO STOCK NUMBER PART NO. SIZE DESIGNATION

1.SCD: Specification Control Drawing / 2.MS: Military Specification / 3.OEM: Original Equipment Manufacturer / 4. USAF: U.S. Air Force Branding military radial tire typical Michelin branding layout

TRADEMARK

INDEX LETTER

CODE IDENTIFICATION

SERIAL NUMBER CODE 15 For details, see page 17

FABRICATION MONTH / YEAR

TYPE NUMBER

MAXIMUM WEAR LIMIT INDICATOR W Application is program dependant 3 - L

COUNTRY OF ORIGIN

CONSTRUCTION SIZE DESIGNATION DESIGNATION

TUBELESS DESIGNATION1 PART NO.

1. All MICHELIN aircraft radials are tubeless Branding bias retread tire RETREADER TRADEMARK

RETREAD AEA TREAD CODE R-LEVEL TUBELESS DESIGNATION MOLDED SKID MONTH & RETREAD SPEED RATING YEAR OF CONSTRUCTION RETREAD DESIGNATION PLY RATING AIRLINE CODE SIZE DESIGNATION

CASING SERIAL PLANT CODE NUMBER 16 Branding radial retread tire

AEA TREAD CODE

MONTH & YEAR OF RETREAD

RETREAD R-LEVEL RATED SPEED PLANT CODE

AIRLINE CODE MOLDED SKID

MKC KANSAS CITY, USA INTERNAL MNW NORWOOD, USA MICHELIN CODE MBO BOURGES, France MCN CUNEO, Italie MNK NONG KHAE, Thailand Michelin tire serial number codes

Radial serial number definition: 9 2 1 1 B 0 2 5

Last number of the manufacturing year (example: 9 for 1999).

3 numbers indicating the manufacturing day in Julian calendar (example: the tire was manufactured the 211th day of the year).

Code letter related to the facility and the decade, see table below.

Unique production identification number.

Bias Serial Number Definition: 9 2 1 1 P 0 0 0 2 5

Last number of the manufacturing 17 year (example: 9 for 1999).

3 numbers indicating the manufacturing day in Julian calendar (example: the tire was manufactured the 211th day of the year).

Code letter related to the facility and the decade, see table below.

Unique production identification number.

Letter signification

The letter code in the tire serial number is used to identify both the manufacturing facility and the decade of manufacture. It follows the rules below:

Manufacturing Through From Jan. 01, 1996 to from Jan. 01, 2000 to Facility Dec. 31, 1995 Dec. 31, 1999 Dec. 31, 2009 included included included

Bourges BB A Clermont-Ferrand FFG Greenville KK L Nong Khae TTW Norwood NP U Safety

18 General safety considerations IMPORTANT: In the event of a conflict between recommended procedures, be sure to contact your Michelin representative before undertaking the procedure in question.

Angle of Approach Recommended Angle of Approach

Aircraft tire and wheel assemblies must Keep pressure hose and fittings inspections. Deflate tires before operate under high pressures in order to used for inflation in good condi- attempting to dismount the tire carry the loads imposed on them.They tion. from the wheel or before disas- should be treated with the same respect Allow the tire to remain in the sembling any wheel component. that any other high pressure vessel inflation cage for several minutes Show caution when removing would be given. Following the after reaching full inflation valve cores as they can be pro- recommended procedures given pressure. pelled at a high speed from the throughout this manual, as well as those Respect inflation pressures and valve stem. provided by authorities such as wheel all other safety instructions. The transportation of a service- manufacturers, air-framers and able aircraft tire/wheel assembly industry regulatory agencies, will Tires in service should be in accordance with minimize the risks and chance of injury. the applicable regulatory body Careful attention should be for the airline. Mounting shown to tire/wheel assemblies Transportation of a serviceable being handled or in storage. inflated aircraft tire is covered by Follow the instructions given in the Never approach a tire/wheel the U.S. Department of section on “General Mounting assembly mounted on an Transportation Code of Federal Instructions For Aircraft Tires”. aircraft that has an obvious Regulations, the International Be particularly attentive when: damage until that tire has cooled Air Transport Association (IATA), to ambient temperatures (allow and other regulatory bodies. Rolling tires on the floor and using at least 3 hours). While serviceable tires may be mechanical lifting equipment to Always approach a tire/wheel shipped fully pressurized in the avoid possible back injuries. assembly from an oblique angle, cargo area of an aircraft, Inspecting tires and wheels in in the direction of the tire’s Michelin’s preference is to advance for possible shipping shoulder. reduce pressure to 25% of damage. Deflate tires before removing operating pressure or 3 bars / them from the aircraft unless the 40 psi, whichever is the lesser. Inflating tire /wheel assembly is to be Remove from service tire/wheel immediately remounted on the assemblies found with one or When inflating tires, be sure to aircraft, such as with brake more tie bolt nuts missing. use a suitable inflation cage. Storage

20 Storing aircraft tires and tubes Tire can be lifted through center Ozone cracking in groove

Typical ozone cracking 21

Tires are designed to be tough, through the center. Avoid the use of molecular bonds and a degradation durable and to withstand large loads forks or other objects which have of the rubber, which lead to crack and high speeds.They can provide corners that could damage the bead initiation. Continued stress, and years of reliable service if a few surfaces. When possible, handle tires especially cyclic stress, causes the precautions are followed. by lifting or rolling. crack to grow until it is visible as the The ideal location for tire and tube characteristic surface crack, storage is a cool, dry and reasonably Avoid moisture and ozone perpendicular to the direction of the dark location, free from air currents applied stress. and dirt.While low temperatures Ozone - What is it ? (not below 0°C/32°F) Designing for ozone are not objectionable, room Ozone is a gas, a form of oxygen. In temperatures above 40°C / 104° F are the earth’s atmosphere, where it To aid in the control of ozone attack detrimental and should be avoided. occurs naturally in small amounts, on rubber, the tire materials specialist ozone plays a crucial geophysical adds waxes and protective chemicals. Handling aircraft tires role because of its intense Some of these ingredients address absorption of solar ultraviolet ozone attack when the tire is in a Care should be shown when hand- radiation. Additional ozone, created static state at room temperature; ling aircraft tires. While tough and when industrial exhaust mixes with other ingredients are activated by durable, tires can be damaged or cut ultraviolet rays, can be harmful. heat and protect the tire once it is in by sharp objects or if excessive force Ozone degrades organic matter, such service. Further, the tire designer is is used. Avoid lifting tires with as rubber. mindful of the impact of shapes and conventional two prong forks of contours on stress concentrations. material handling trucks. Damage Impact of ozone on tires Still, steps need to be taken in storage to bead mounting areas or the to delay the effects of ozone attack. innerliner can occur. A wide, flat, Most of the natural and synthetic Wet or moist conditions have a pincher type fork assembly of the elastomers used in aircraft tires are deteriorating effect on tires and type that lifts the horizontal tire by susceptible to ozone attack. tubes, and can be even more squeezing against the tread surface Ozone in the air readily reacts with damaging when the moisture is recommended. An alternate the double bonds (unsaturation) in contains foreign elements that are recommended method would be the rubber molecules. The result of further harmful to rubber and cord to use a rounded bar to lift the tire this reaction is the breaking of fabric. Storing aircraft tires and tubes

Horizontal storage is not recommended

22 Protect tires from contaminants Store tires vertically in racks

Strong air currents should be If tires accidentally become Fluorescent or mercury vapor lights avoided, since they increase the contaminated, wash them off with should not be used because they supply of oxygen and quite often denatured alcohol and then with a generate ozone. Low intensity carry ozone, both of which cause soap and water solution. After sodium vapor lights are rapid aging of rubber. cleaning, be sure to remove any recommended. See the section on Particular care should be taken to water that may have accumulated “Ozone” for more information. store tires and tubes away from in the interior of an unmounted tire. fluorescent lights, electric motors, If after cleaning, the surface Stores tires vertically battery chargers, electric welding of the tire appears soft, or spongy, equipment, electric generators and or bulges are present, the tire is not Whenever possible, tires should be similar electrical devices, since they suitable for service. Should you have stored in regular tire racks which all create ozone. any doubt about the serviceability hold them up vertically. The surface of such a tire, please contact your of the tire rack on which the weight Store away from fuel Michelin Representative or of the tire rests should be flat and, if and solvents authorized repair station. possible, 3 to 4 inches / 7.5 to 10 cm wide to prevent permanent Make sure that tires do not come Store in the dark distortion of the tire. into contact with oil, gasoline, jet fuel, hydraulic fluids or other The storage room should be dark, Horizontal stacking of tires hydrocarbon solvents, since all of or at least free from direct sunlight. is not recommended these are natural enemies of rubber Windows should be darkened with and cause it to disintegrate rapidly. a coat of blue paint or covered with If tires are stacked horizontally, they Be especially careful not to stand or black plastic. Either of these will may become distorted, resulting lay tires on floors that are covered provide some diffused lighting in mounting problems. This is with oil or grease. When working on during the daytime. Black plastic particularly true of tubeless tires. engines or landing gears, tires is preferred since it will lower the Those on the bottom of a stack may should be covered so that oil does temperature in the room during the have the beads pressed so closely not drip on them. warm months and permit tires to be together that bead spreader tools stored closer to the window. will have to be used to properly space the beads for contact with the wheel during initial inflation. 23

Tires which are stacked on top done as a temporary measure. Note: Certain regulatory agencies of each other, sidewall-to-sidewall, Before mounting a tire and tube recommend further restricting have increased stresses in the tread stored in such a manner, always the age of rubber products grooves. If tires are stored for remove the tube from the tire and used in the aircraft industry. an extended period of time, or in inspect the inside of the tire for The decision to adopt these an environment with high ozone foreign material, which, if not recommendations must be concentration, ozone cracking cleaned out, could cause irreparable made by the individual user. is most likely to form in the tread damage to both tube and tire. grooves. Under no circumstances should Storage of inflated tire If tires must be stacked, they should tubes ever be hung over nails or and wheel assemblies not be stacked for more than pegs, or over any other object which 6 months maximum. The maximum might form a crease in the tube. Mounted tire/wheel assembly stacking height: Such a crease will eventually properly prepared and delivered to produce a crack in the rubber and a line maintenance station as an 3 tires high if tire diameter is cause tube failure. airworthy replacement unit may be greater than 40 inches / 1 meter. stored at full operational pressure 4 tires high if tire diameter is less Tire or tube age limit for up to 12 months, see comments than 40 inches inches / 1 meter. in the section on tire mounting Michelin aircraft tires or tubes have found later in this manual. Store tubes properly no age limit and may be placed in service, regardless of their age, Michelin tubes should always be provided all inspection criteria for stored in their original cartons, so service/storage/mounting and they are protected from light and air individual customer-imposed currents. If stored without their restrictions are met. cartons, they should be wrapped in several layers of heavy paper. Tubes can also be stored by inflating slightly (not more than 0.06 bar / 1 psi) and inserting them in the same size tire. This, of course, should only be Ozone

24 Aircraft tires and ozone 25

Recommendations Location: for storage and handling Inside a warehouse away from direct sunlight or precipitation. (Wet or moist conditions can carry other chemicals which can have The following storage and handling a further damaging effect on tires.) conditions are strongly recommended Storage Area Environment: to minimize the damaging effects of ozone: Temperatures should remain between 0°C/32°F and 40°C/104°F. Use reasonably low intensity lighting (sodium vapor lamps are preferred). Environment should be free of strong air currents and excessive dirt. Ozone Sources: Store away from fluorescent lighting, mercury vapor lamps, electric motors, battery chargers, electric welding equipment, and electric generators. Tire Storage: Stand the tire such that it rests on its tread, whether on the floor or in a rack. This orientation should be used for any tire which will be held in storage for more than 1 months time. (Storage racks should provide an adequate amount of surface area to support the tire to prevent a distortion or “set” from occurring in the tread area). If high ozone concentrations can not be reduced or eliminated, each tire should be protected by appropriate wrapping such as dark polyethylene or paper. Mounted Tire: Mounted tires not immediately placed in service should be covered or wrapped until they are to be installed on an aircraft. To minimize the effects of ozone attack and where re-inflation capability exists, tire pressure may be reduced to a value below operational pressure, but not less than 25% of the operational pressure or 40 psi / 3 bars, whichever is less. General mounting

26 General mounting instructions for aircraft tires Wheel half and O-Ring 27

General Premounting checklist Direct particular attention to the following: Proper mounting procedures simplify Wheels Ensure that the bead seating the job of servicing aircraft tires, area of the wheel is clean and while at the same time increasing Careful attention to details is neces- uncontaminated. safety and reducing the chances of sary to successfully mount aircraft damaging tires or wheels. tires for trouble-free service. Make Mating surfaces of the wheel Do not mount aircraft tires without sure you are thoroughly familiar halves should be free of nicks, the proper equipment, instructions, with and inspect all key wheel parts burrs, small dents, or other before beginning to mount a tire. and operator training. damage that could prevent the surfaces from properly mating To assist in this process, wheel Be sure to know and understand all or sealing. Painted or coated chemicals used on the tire and wheel. manufacturers publish specific surfaces should be in good It is possible that under the high instructions in their maintenance condition; not badly chafed, pressures and load exerted by the tire and overhaul manuals. Follow their chipped, etc. on the wheel, normally inert chemi- recommendations and procedures cals may contribute to rapid corro- for wheel assembly and disassembly Be sure fuse plugs, inflation sion and/or abrasion of the wheel, or to obtain trouble-free mounting and valves and wheel plugs are in deterioration of the rubber surface. dismounting. good condition, properly sealed against loss of pressure and Virtually all modern aircraft wheels correctly torqued per the are of two types: split wheel type, i.e., manufacturer’s instructions. two “halves” joined by removable tie bolts, or the removable flange type. 0-Ring grooves in the wheel Both designs facilitate the mounting halves should be checked (and dismounting) of the tire. Show for damage or other debris careful attention in handling, assem- that would prevent the 0-Ring bling and disassembling wheel com- from properly seating. ponents to avoid damage to critical surfaces. General mounting instructions for aircraft tires

PACKING Position Light Spot May Be Stamped On Wheel

INNER WHEEL OUTER WHEEL HALF ASSEMBLY HALF ASSEMBLY

FIXTURE PACKING TIE BOLT NUT

WASHER WASHER

TIRE 28 Aircraft Tire/Wheel Assembly

O-Rings themselves must be Tires • Contamination from foreign of the proper material, as substances (oil, grease, brake specified by the wheel manufac- Before mounting any tire, verify that fluid, etc.) which can cause turer, for the intended application the tire is correct for the intended surface damage (blisters or and temperature conditions. application. swelling). Inspect O-Rings for cracking, Use the following checklist: cuts, or other damage. Particular Inspect the inside of the tire attention should be given to Check that the tire markings to be sure there is no foreign permanent deformations in the are correct for the required material present. Be sure that O-Ring. O-Rings found with application (size, ply rating, the inner liner condition is good, deformations should be replaced. speed rating, part number, TSO that is, without wrinkles. Check Proper sealing of the wheel marking). for liner damage caused by halves is critical in providing improper shipping or handling trouble-free service. Visually inspect the outside of the tire. of the tire for: Should the inspection of a • Damage caused by improper Refer to the section on “Tire used O-Ring for its integrity shipping or handling of the tire. Serviceability Criteria” for damages. not be practical or manageable, • Cuts, tears or other foreign If in question, tires should not be replace with a new O-Ring with objects penetrating the rubber. used and should be returned to a each tire change. • Permanent deformations. certified repair or retread station for • Debris or cuts on the bead further inspection and disposition. seating surfaces. Clean the tire bead surfaces with either a clean shop towel, a soap/water solution, or with denatured alcohol as may be necessary. • Bead distortions. • Cracking that reaches cords. 29

Mounting Lubricants manufactured from a When mounting tube-type tires, petroleum base are not recommen- dust the tube and the inside of the Use of Inner Tubes ded as hydrocarbons have a known tire with tire talc or soapstone before detrimental effect on rubber installing the tube. This will prevent Bias Tires compounds. the tube from sticking to the inside All Michelin bias or cross ply tires, of the tire or to the tire beads. whether tube-type or tubeless, are Radial Tires Dusting also helps the tube assume suitable for operation with tubes For radial tires, use of a mounting its normal shape inside the tire approved for the particular tire size lubricant is not specified, unless during inflation, and lessens the and application on tube-type wheels. approved by the airframer. chances of wrinkling or thinning from irregular stretching. (Caution: Radial Tires Tire/Wheel Assembly Use care not to damage tube when All Michelin radial tires are of mounting.) tubeless design. Never use an inner Again, be sure that the wheel, tire, tube or mount on a tube-type wheel. and assembly components are in To be consistent with the practice of good condition and free of debris. mounting the tire serial number to Lubrication of Tire Beads the outboard wheel half, tubes should Lubricate the O-Ring (as specified be installed in the tire with the valve Bias Tires by the wheel manufacturer) and projecting on the serial numbered Because of their typically wide bead install in the wheel groove or side of the tire. flat, when installing bias tires on channel. Be sure the O-Ring is free of aluminum wheels, lubricate the toes kinks or twists. Assemble the two wheel halves, of the beads with an approved 10% being sure to align the light point of vegetable oil soap solution. Position the previously inspected each half 180° apart to insure the tire in front of the first wheel half. optimum balance of the assembly. Do not use lubricant with magne- If a bias tire, lubricate the beads as sium alloy wheels! required. Slide the tire on the wheel. When aligning the wheel halves, be careful not to damage the O-Ring in the wheel base which seals the wheel halves. General mounting instructions for aircraft tires

WARNING! Aircraft tires can be operated up to or at rated inflation pressure; extremely high inflation pressures may cause the aircraft wheel or tire to explode or burst, which may result in serious or fatal bodily injury. Aircraft tires must always be inflated with a properly regulated inflation canister. The high pressure side should never be used. The safety practices for mounting and dismounting aircraft tires detailed in this Manual must 30 be followed. Tire balance mark

Tire/Wheel Alignment for Balance A properly balanced tire/wheel cage and attached to the wheel assembly improves the tire’s overall valve.This arrangement allows the The “red” balance mark on the lower wear characteristics. In addition to tire service person to inflate the tire sidewall indicates the light point of severe vibration, an unbalanced safely using the remote valve. the tire’s balance. Align this mark with assembly will cause irregular and the heavy point of the wheel. localized tread wear patterns that Inflating With Nitrogen In the absence of a balance mark, can reduce the overall performance align the tire’s Serial Number with life of the tire. Many regulatory agencies require the the heavy point of the wheel (main use of nitrogen when inflating tires landing gear position tires only). Be sure that nuts, washers, and bolts for aircraft above a specified Many wheel manufacturers today are installed in proper order and that Maximum Take-Off Weight (MTOW). identify either the light spot or heavy the bearing surfaces of these parts Michelin recommends the use of a spot of the wheel with markings in the are properly lubricated as required. dry, commercial grade nitrogen of at flange area. Follow their instructions Tighten to manufacturer’s least 97% purity when inflating all on assembly and balance. Be sure to recommended torque values. aircraft tires. Nitrogen provides a align the tire’s light spot 180° from the stable, inert inflation gas while wheel’s light spot or directly in line After the tire is mounted on the eliminating the introduction of with the wheel’s heavy spot. In the wheel, the assembly should be moisture into the tire cavity. absence of specific wheel markings, placed in a safety cage for inflation align the tire’s red balance mark with with nitrogen. It is recommended Aircraft operating procedures for the wheel inflation valve. that the cage be placed against an initial inflation and adjustments must Some aircraft tubes feature balance outside wall that is strong enough to comply with applicable instructions as marks to indicate the heavy portion of withstand the effects of an explosion given in FAR 25 or JAR 25. the tube. These marks are of either the tire, tube or wheel. approximately 1/2” wide and 2” long. Oxygen concentration should never When inserting the tube in the tire, its The inflation pressure source should exceed 5%. balance mark should be aligned with be located 10 meters / 30 feet away the balance mark on the tire. If the from the safety cage with a valve, tube has no balance mark, align regulator and pressure gauge the valve with the balance mark installed at that point.The inflation on the tire. line should then be run to the safety Tire / Wheel Assembly

Inflate Tire to Aircraft Operating Pressure PN

Check and Repair 3 hours if Leakage

Check Inflation Pressure

If PN < 90%

If PN ≥ 90% Basic Pressure Retention Procedure Inflate Tire to Aircraft Operating Pressure PN 12 hours Check Inflation Pressure

If PN ≥ 97.5% Accept Assembly

If PN < 97.5%

Inflate Tire to Aircraft Operating Pressure PN 24 hours Check Inflation Pressure

If PN ≥ 97.5% Accept Assembly

If PN < 97.5% Repair or Reject 31

Special Procedure To Properly Basic pressure retention check For safety: use a suitable metal Seat Tube-Type Tires inflation cage when inflating Pressure retention checks are designed tires. To seat tire beads properly on the to verify that tire/wheel assemblies wheel: meet industry standards for pressure 2 Store the inflated tire/wheel Inflate the tire to the recommen- retention prior to releasing them for assembly for 3 hours. ded pressure for the aircraft on service on aircraft.This important 3 Check inflation pressure: which it is to be mounted. process assures reliable service and Be sure that the ambient Next, completely deflate the tire. avoids costly returns for repairs. temperature of the tire/wheel Finally, reinflate it to the correct This basic pressure retention check assembly has not changed pressure (do not fasten the valve requires approximately 15 hours to by more than 3°C/5°F. to the rim until this has been determine if an assembly can be Options: done). Use a valve extension for accepted for service. Additional • If inflation pressure is equal to inflation purposes if necessary. ≥ checks are performed on tire/wheel or greater than ( ) 90% of the specified operating pressure, This procedure helps remove any assemblies not meeting the minimum acceptance criteria for pressure loss. proceed to Step 4. wrinkles in the tube and helps • If inflation pressure is less than prevent pinching the tube under the To follow this procedure requires a (<) 90% of the specified opera- toe of the bead. It eliminates the ting pressure, inspect the possibility of one section of the tube pressure gauge of 0.25% accuracy or better and capability to indicate assembly for leakage. Use a stretching more than the rest and soap solution on tire beads and thinning out in that area. Further, it 2 psi / .15 bar pressure change. other susceptible wheel com- assists in the removal of air that ponents (valves, fuse plugs, might be trapped between the inner Procedure: over-pressurization plugs, tube and the tire. 1 Inflate the newly mounted wheel half parting line, etc.). Note: With tubeless tires, this tire/wheel assembly to operating If soap bubbles or leaks are inflation-deflation-reinflation pressure for the aircraft found, make appropriate procedure is not necessary. application as specified in shop repairs. Return to Step 1. instruction manuals. 4 Re-inflate the tire to the specified operating pressure. General mounting instructions for aircraft tires

Emergency Pressure Retention Procedure

Tire / Wheel Assembly Install Tire on Aircraft Emergency pressure Inflate Tire to Aircraft at Operating Pressure Operating Pressure PN retention check: PN + 5% (unloaded) Within 30 minutes The following procedure Check Inflation Pressure may be used to perform Spray with leak before each flight over a pressure retention check detection solution the next 48 hours on a newly mounted If bubbles are found on Submit tire/wheel assembly when wheel hardware assembly If PN ≥ 90% Accept Assembly time does not allow the or a stream of bubbles at for Basic tire vents… basic procedure to be pressure applied. Note this procedure check If PN < 90% If no bubbles are found at recommends a tire inflation plugs, valves, “O-rings”, or Remove the assembly check be performed before no stream of bubbles at tire vents… (and mate) per the each flight during the first inflation pressure 48 hours after the assembly 32 maintenance schedule has been put into service.

5 After 12 hour storage period, If soap bubbles or leaks are Alternate pressure check inflation pressure: found, make appropriate retention check Be sure that the ambient repairs. Proceed to step 6. temperature of the tire/wheel This alternate, historical, procedure is 6 assembly has not changed Re-inflate the tire to the specified designed to provide a more complete by more than 3°C/5°F. operating pressure. check of tire/wheel assembly pressure retention prior to releasing them Options: 7 After a 24 hour storage period, for use on aircraft.The procedure • If inflation pressure is equal to check inflation pressure. Be sure is particularly beneficial when ≥ or greater than ( ) 97.5% of the that the ambient temperature of in-service pressure retention issues specified operating pressure, the tire/wheel assembly has not have been encountered. accept the tire/wheel assem- changed by more than 3°C/5°F. bly for in-service usage or line Procedure maintenance storage (see Options: Storage Section for recom- • If inflation pressure is equal to or Allow for Tire Growth mendations on line mainte- greater than (≥) 95% of the Newly mounted tire/wheel assem- nance storage). specified operating pressure, blies should stand for 12 hours to accept the tire/wheel assembly allow for normal tire growth (cord Note: Re-inflate tire to the for in-service usage or line main- body stretching) and to verify that specified operating tenance storage (see Storage the assembly is without leaks. pressure. Section for recommendations on After 12 hours, inspect the assem- line maintenance storage). bly carefully. Check the tire pres- • If inflation pressure is less than sure drop. A 10% drop during tire (<) 97.5% of operating pressure, Note: Re-inflate tire to the growth is considered normal. inspect the assembly for leakage. specified operating More than that may indicate a lea- Use a soap solution on tire pressure. kage problem. Be sure that the tire beads and other susceptible assembly has remained at a cons- • If inflation pressure is less wheel components (valves, fuse tant ambient temperature (± than (<) 95% of operating plugs, over-pressurization plugs, 3°C/5°F). A drop of 3°C/5°F will pressure, reject the tire/wheel wheel half parting line, etc.). reduce inflation pressure 1%. assembly. Sidewall vent holes

Check for Leakage escape through special sidewall vents. Note: Do not identify a tire as a After the growth period, reinflate Tires requiring vent holes have them leaker solely on the rate of the tire to the specified operating placed in the lower sidewall. This bubbles from these vent pressure. Recheck the pressure venting prevents pressure build-up holes. A high rate of bubble after a 24-hour period. A pressure within the carcass body which might venting is not always an loss of 5% or less is considered cause tread, sidewall, or ply indicator of tire leakage. normal. Be sure that the ambient separations. The location of It is best to judge excessive temperature of the tire has not each vent hole on the new tire is leakage of a tire/wheel assem- changed by more than 3°C/5°F. If indicated by a colored paint dot. bly based on pressure loss as a greater than 5% pressure loss Simply apply a soap solution to measured with a occurs, investigate the tire/wheel these vent markings. The calibrated gauge, preferably assembly for leaks. Do not put the appearance of small bubbles will the same gauge used to tire into service until the leak indicate diffusion. This bubbling is initially inflate the tire. source is identified and corrected. normal and may be seen at any time If the pressure loss is within the while the tire is inflated. Maximum Not all aircraft tires are vented acceptable 5% limit, the assem- allowable diffusion is 5% for any bly is now ready to be installed 24-hour period. Pressure losses in Improvements in materials, tire design on the aircraft. excess of 5% may indicate leakage and fabrication make the need for Note that once in service, the from other sources. In that case, the lower sidewall venting unnecessary for tire/wheel assembly maximum tire and wheel assembly should be all aircraft tires. This is particularly daily (24 hours) pressure loss is carefully tested for leaks, preferably true for the physically smaller tires 5%. Typical rates are 0.2-2.0% by total immersion, before placing such as General Aviation and High per 24-hour period. it into service. If no assembly leaks Performance Military tires. are found, dismount and have the Sidewall venting tire inspected by the manufacturer Knowing which tires have been or a qualified repair shop. vented is important. Tires requiring Aircraft tires have traditionally been lower sidewall vents will have either designed to permit any air or nitrogen a green or white paint dot applied to trapped in the cord body or that the area of each vent hole. Tires not diffuses through the liner or tube to needing lower sidewall vents will have no color dot in this zone. General mounting instructions for aircraft tires

Storage of an inflated tire It is acceptable to STORE the • Shop re-inspection should be and wheel assembly mounted assembly pressurized made with the assembly infla- in this range for up to ted to the operational pressure Once a tire has been properly mounted 12 months. After 12 months, level. The entire exterior of the and the assembly verified for pressure any inflated assembly which tire should be visually inspec- retention, only minimal precautions has not been introduced into ted for cracking (due to ozone need be taken. service should be returned to or ultraviolet attack), damages, the wheel mounting shop. or any other condition. If the Do not expose the tire to The following inspections and limits given in the chapter on excessively high temperatures actions should be taken with “Tire Serviceability Criteria” (greater than 40° / 104° F). the assembly before returning have been exceeded, dismount it to service. This storage and the tire from the wheel and Do not expose the tire to re-inspection interval can be return to the supplier. direct sunlight or to high ozone repeated multiple times so concentrations. long as the tire meets all Subject the assembly to the criteria. However, to maximize standard air retention test to Avoid contact with tire life, it is recommended to verify that the assembly will contaminants (oil, grease, etc.). rotate replacement stock. still meet the criteria of no more than 5% pressure loss in A Mounted tire/wheel Note: The conditions of storage, and a 24 hour period. assembly properly prepared the tire’s response to those and delivered to a line mainte- conditions, will determine While in storage, if the nance station as an airworthy whether a stored, inflated tire assembly inflation pressure replacement unit should meet is still airworthy. Time should was being maintained using the following storage conditions: not be the measure by which a compressed air, deflate the tire is classified unserviceable. assembly and re-inflate with • The pressure level should be nitrogen (per industry set at operational pressure for standards). the tire application. Do not exceed operational pressure. 35

Having met each of the above Transportation of a serviceable conditions, return the inflated aircraft tire is covered by the tire/wheel assembly to stock. U.S. Department of Transportation Code of Federal Regulations, Note: The criteria for re-inspection the International Air Transport of the wheel must also be Association (IATA), and other determined before returning regulatory bodies. the assembly to service. While serviceable tires may be • To minimize the effects of shipped fully pressurized in the ozone attack and where re- cargo area of an aircraft, Michelin’s inflation capability exists, tire recommendation is to reduce pressure may be reduced to a pressure to 25% of operating value below operational pres- pressure or 3 bars / ~40 psi, sure, but not less than 25% of whichever is the lesser. Reinflate to the operational pressure or operating pressure before mounting 40 psi / 3 bars, whichever is less. on the aircraft.

Transportation of a serviceable aircraft tire/wheel assembly should be in accordance with the applicable regulatory body for the airline. Mounting on aircraft

36 Mounting tire/wheel assembly on the aircraft 37

Visually Inspect Tire/Wheel Readjust Tire Pressure Important: Assembly Readjust Tire Pressure after • Check pressure with aircraft load on tire. Visually Inspect Tire/Wheel mounting the tire/wheel assembly Assembly for damage from on the aircraft. Operating pressures • Use loaded operating inflation handling, storage, or are set by the airframe pressure. contaminants. Look for manufacturers based on a variety of deformations, bulges, swelling, factors including maximum ramp or • Operational pressure values are blisters, or other anomalies that taxi weight, center of gravity and for loaded tires. would make the assembly dynamic loading. Reference the unserviceable. Operator’s Manual for the particular aircraft. • Loaded inflation pressure = 104% Superficial cuts or cracks not unloaded inflation pressure. reaching the cord body are acceptable for service.

Groove cracking that does not reach the protector or reinforcing ply is acceptable for service.

Follow the guidelines given in this Manual for serviceability. Inflation pressure maintenance

38 Inflation pressure maintenance 39

Proper inflation - getting Be particularly alert to severe Effects of Underinflation the most out of your tires temperature drops, which will also reduce tire pressure. Repeated Too little pressure can be harmful to The most important service you can pressure losses beyond the daily 5%, your tires and dangerous to your perform on your aircraft’s tires is to under constant temperature aircraft and those in it. conditions, may signal a slow leak in Underinflated tires can creep or slip make sure they are properly inflated the tire/wheel assembly. on the wheel under stress or when at all times.The more often you use brakes are applied. Valve stems can the aircraft, the more often the tires To avoid false readings, tire pressure be damaged or sheared off and the need checking. It is the Key to should be checked on “cool” tires tire, tube, or complete wheel Optimum Service. (air in a hot tire will expand, causing assembly can be damaged or a temporary higher pressure destroyed. Excessive shoulder wear If you make one or more flights a reading). Wait at least 3 hours after may also be seen. day, tire pressure should be checked landing or until the tire has reached daily, with an accurate, calibrated ambient temperature as noted by Underinflation can allow the gauge (preferably with a dial or carefully feeling with the palm of the sidewalls of the tire to be crushed by digital indicator appropriate for the hand, before making pressure the wheel’s rim flanges under pressure range of your tires). checks. landing impact, or upon striking the When installed, the TPIS (Tire edge of the runway while Pressure Indicator System) can be If it is absolutely necessary to check maneuvering. Tires may flex over the used to make the daily inflation pressures when tires are hot, wheel flange, with the possibility of pressure check, provided the TPIS compare the relative pressures damage to the bead and lower indicators are verified against a between tires on the same landing sidewall areas. The result can be a calibrated pressure gauge at each gear positions (main or nose). Never bruise, break or rupture of the cord aircraft “A” check. bleed pressure from a hot tire [See body. In any case where the bead or “Checking Hot Tires” later in this cord body of the tire is damaged, the If you fly less than one time per day, section for details]. tire is no longer safe to use and must you should check tire pressure be replaced. before each flight. Inflation pressure maintenance

40 Standing Wave in Laboratory conditions.

Severe underinflation may cause ply WARNING! Aircraft tires can be ope- Checking Duals for Equal separation and carcass degradation rated up to or at rated inflation Operating Pressure because of the extreme heat, pressure. Extremely high inflation the strain caused by the excessive pressures may cause the aircraft Tires mounted as duals or on the flexing action, or the occurrence wheel or tire to explode or burst, same bogey, whether main or nose, of premature standing waves which may result in serious or fatal whether bias or radial, should be (see photo). This same condition can bodily injury. Aircraft tires must maintained at equal operating cause inner tube chafing and a always be inflated with a properly pressure. If pressures are not equal, resultant blowout. regulated inflation canister.The the tire with the highest pressure will high pressure side should never be be carrying an unequal proportion In dual tire applications, used. The safety practices for moun- of the load even though there may underinflation of one tire causes the ting and dismounting aircraft tires be no perceptible difference other tire to carry a disproportionate detailed in this Manual must between tire deflections. amount of load. As a result, both tires be followed. The graph on page 41 demonstrates can be deflected considerably beyond this concept. their normal operating range, potentially causing ply separations If it is determined that dual- and/or carcass degradation. mounted tires are operating at unequal pressures (more than 5% Effects of Overinflation is cause for special attention), inflate both tires to their proper pressure. Tires operating under too much Make a logbook entry indicating the inflation pressure are more original pressure differential, the susceptible to bruising, cuts and date and time corrected and the shock damage. Ride quality as well ambient temperature. At each as traction will be reduced. subsequent pressure check, the Continuous high pressure operation logbook should be consulted. will result in poor tire wear characteristics (center wear) and reduced landings performance. Effects of Unequal Tire Pressure on Tire Loads

200% Strut load 200% Strut load 100% pressure 100% pressure 60% pressure 100% pressure 100% load 100% load A load B load

60% 100%

Pressure

Rated Deflection

80% 100% 120% A Load B Dual Tire Axle

If the same tire continues to When required, reinflate tires to Loaded versus Unloaded Tires evidence a pressure loss, it should be their specified operating pressure checked for leakage (FOD, valve with a dry, commercial grade Be sure that it is clear whether core, etc.). If no obvious cause is nitrogen of at least 97% purity. operating inflation pressures are found, the tire should be removed given for loaded or unloaded tire and given a thorough inspection In some cases, nitrogen may not be conditions. A tire’s inflation pressure until the reason for the pressure loss available for adjusting tire inflation. when loaded will be 4% higher than can be determined. When this occurs, clean dry air may when unloaded (Loaded pressure = be used as long as the oxygen 1.04 x unloaded pressure). For mixability of bias and radial content does not exceed 5% of the tires, see the section on “Matching total tire volume. If the 5% oxygen Properly Inflating Tube-Type Tires Dual Tires” in this manual. limit is exceeded, the tire must be deflated and then reinflated with Air is usually trapped between the Proper Inflation - Setting the nitrogen to the specified operating tire and the tube at the time of Pressure Level pressure. mounting. Although initial readings indicate proper pressure, the Inflating and Reinflating WARNING! In the event of excessive trapped air will seep out around the the Tire/Wheel Assembly heat build-up in the tire/wheel valve stem hole in the wheel, and assembly (example, locked brakes), under the beads. Within a few days, Whether for tubeless or tubetype, hydrocarbons released by the tire as the tube expands to fill the void tire operating pressures should be may spontaneously ignite in the left by the trapped air, the tire may set following the instructions given presence of oxygen. become severely underinflated. To by the airframe manufacturer. For A tire filled with air can explode, compensate for this effect, check tire newly mounted tires, follow the causing injury to persons and pressure before each flight for instructions given in the section on damage to equipment. several days after installation, “General Mounting Instructions For adjusting as necessary, until the tire Aircraft Tires.” maintains proper pressure. Inflation pressure maintenance

Metric Units

∆50 12.9 14.1 16.4 17.6 ∆40 12.5 13.7 15.9 17.1 Temperature Rise °C ∆30 12.1 13.2 15.5 16.6 ∆20 11.8 12.8 15.0 16.0 ∆10 11.4 12.4 14.5 15.5 Specified Operating 11 12 14 15 Pressure (bars) ∆10 10.6 11.6 13.5 14.5 ∆20 10.2 11.2 13.0 14.0 Temperature Drop °C ∆30 9.9 10.8 12.5 13.4 ∆40 9.5 10.3 12.1 12.9 ∆50 9.1 9.9 11.6 12.4 42 Units in °C and Bars

Effect of ambient temperature The above charts are a helpful on gauge pressure example of the change in inflation pressure readings as a result of a Effect of Temperature change in ambient temperature. For convenience, it is given in metric Watch for severe changes in ambient units and in customary units. temperature. Changes in temperature affect gauge pressure readings as follows:

1% change (increase) in inflation pressure reading for every 3°C/5°F change (increase) in temperature. Customary Units

∆100 192 216 240 264 ∆80 186 209 232 255 Temperature Rise °F ∆60 179 202 224 246 ∆40 173 194 216 238 ∆20 166 187 208 229 Specified Operating 160 180 200 220 Pressure (bars) ∆20 154 173 192 211 ∆40 147 166 184 202 Temperature Drop °F ∆6O 141 158 176 194 ∆80 134 151 168 185 ∆100 128 144 160 176 Units in °F and PSI 43

Proper Inflation – Standard for Aircraft experiencing large or Maintaining Pressure Level ambient temperature When pressure maintenance differences between airports is available at the destination A “cold” tire is defined as a tire which airport, check and readjust to has come to equilibrium with its Large temperature differences place operating inflation pressure (PN) operating environment (ambient a special burden on aircraft prior to the next flight. temperature). operations. As can be seen in the chart above, large changes in In all other cases, maintain the While the actual (ambient) temperature ambient temperature will result in inflation pressure per the standard of the “cold” tire will vary from location corresponding changes in gauge recommendation. to location and from season to season, pressure. Aircraft flying long the operational inflation pressure (PN), distances where a large (>30°C/54°F) as specified by the airframe decrease in ambient temperature manufacturer for each aircraft will occur need to apply specific configuration, is necessary to carry the inflation maintenance procedures. load of the aircraft. This pressure value One of two options should be is therefore needed regardless of the selected in this situation: ambient temperature. For example, if PN = 12 bars / 175 psi, this is In the event that pressure main- the pressure needed at any ambient tenance is not available at the temperature. destination airport, raise the operating inflation pressure (PN) by Note: Do not reduce the pressure 1% for each 5° F / 3° C temperature of the “cold” tire subjected drop relative to the departure air- to frequent changes port to insure adequate inflation in ambient temperature. pressure in the assembly at the destination airport. [Refer to P.44 for additional guidance.] Note: Do not exceed maximum rated loaded tire pressure. Inflation pressure maintenance

Schedule and action

Measured Pressure as % of Operating Tire Condition Course of Action Pressure

More than 105 Overinflated Because of variations in ambient temperature, gauge accuracy, etc., caution should always be shown before adjusting an overinflated pressure.

It is recommended that the first overinflated reading be recorded in the aircraft log along with the ambient temperature. After the 2nd confirmed reading >5%, readjust tire pressure to maximum of normal operating range.

105 -100 Normal Operating Do not adjust tire pressure. Pressure Range Do not exceed tire’s maximum rated pressure value (loaded), nor the wheel’s TSO qualification pressure value (loaded).

100 - 95 Acceptable Daily Readjust tire pressure to maximum of normal Pressure loss operating pressure range. 44 Continued on page 45

When to Check Checking Hot Tires Because of unusual circumstances, it may be necessary to check Frequency Knowing if the pressure of a hot the pressure of a tire when it is hot. tire is correct is nearly an For example, check pressure if: Tires in service should have their impossible task. The air in a hot “cold” inflation pressure checked tire expands, causing a temporary • tire shows excessive deflection daily to properly maintain higher pressure reading. The operating pressures. For aircraft exact temperature is not known • flight schedules make it operating on a less frequent basis, and thus the relative pressure is impossible to make a routine inflation pressure should be also unknown. As the tire cools, pressure check on a cool tire checked before each flight. its pressure is also changing and will continue to do so until • tire is continually exposed to When installed, the TPIS (Tire ambient temperature is reached. direct sunlight. Pressure Indicator System) can be used to make the daily inflation A hot tire is one that has dynamically While no precise procedure can be pressure check , provided the rolled under load on the aircraft and given for checking the pressure of a TPIS indicators are verified has not been allowed to reach hot tire, the following instructions against a calibrated pressure ambient temperature (not been and precautions should be followed. gauge at each aircraft “A” check. allowed to cool for at least three Understand that tires are capable hours). Tires at elevated of retaining pressure to temperatures will develop inflation tolerances which will keep them pressures higher than the specified well within 5% of the specified cold inflation pressure. pressure each day. Since pressure losses due to other causes can seriously affect performance and safety, it still remains a recommended practice to verify the pressure value at least daily. Schedule and action

Measured Pressure as % of Operating Tire Condition Course of Action Pressure

Continued from page 44 94 - 90 Accidental Readjust tire pressure to maximum of normal Pressure Loss operating pressure range. Record in log book.

Recheck pressure after 24 hours.

If after 24 hours, pressure loss is again greater than the daily acceptable pressure loss (>5%), remove tire/wheel assembly. * If it is known Inspect tire/wheel assembly for cause that a major of pressure loss. pressure loss occurred while 89 - 80 Pressure Loss Remove tire/wheel assembly from aircraft. the aircraft was at rest or parked Reinflate to specified operating pressure. and the wheels If pressure loss is within daily acceptable did not turn pressure loss allowance (<=5%), accept assembly. with weight on them, the tire If pressure loss is outside the daily acceptable pressure loss allowance (>5%), inspect tire/wheel assembly and the adjacent for cause of pressure loss. tire can be saved. If doubt If the cause cannot be found, dismount tire for exists, tag the inspection by an authorized repair station. tire(s) and have 79 - 0 Major Pressure Loss Remove the tire/wheel assembly. an authorized retread repair Remove the adjacent tire/wheel assembly. station inspect them. Replace tires*. 45

Compare tire pressures on • The basic rules to follow for Note: If one tire has an abnormally the same given landing gear correcting inflation pressure of high pressure (>5%) as hot tires on the same landing compared to the other tires on • Pressures measured from tires gear: that gear, look for possible on the same landing gear causes such as faulty brakes or should be of the same magni- Single and Multiple tire gear - incorrect pressure adjustment tude. They should always be Should always be at least equal at previous check. at least equal to the specified to, and may exceed, the specified operating pressure. operating pressure. Monitoring Inflation Pressure - What To Do • If any tire is less than 90% of Two tire gear - If one tire minimum loaded service pres- is approximately equal in Checking and monitoring inflation sure, remove the tire from ser- temperature but low in pressure pressure is usually performed on vice. it should be brought up to the loaded tires. Be sure to know pressure level of the other tire. whether the operating inflation In such cases, note reason for In all cases, both tires should be pressure is for loaded or unloaded removal and return the tire to at least equal to or greater than tire conditions. an authorized repair facility the specified operating pressure. for examination. Loaded inflation pressure is 1.04 x Three or more tire gear - Unloaded inflation pressure. • Aircraft flying between airports Check all tires on the gear. with a significant temperature Any tire that is approximately Use an accurate, calibrated drop, should be aware of the equal in temperature but low in gauge, preferably with a dial type effects of temperature on pressure should have its inflation indicator. inflation pressure. See section increased such that all tires are “Effects of Temperature.” within a 5% pressure range. Watch for changes in ambient In all cases, all tires should be temperature. A 3°C/5°F Do Not Reduce The Pressure of at least equal to or greater than temperature change will result a Hot Tire. the specified operating pressure. in a 1% tire pressure change. Inflation pressure maintenance

180

160

140 1% loss rate 120

100

80 3% loss rate 60

40 Inflation Pressure (psi) 5% loss rate 20 Pressure loss more than 5% daily - reinflate to operating pressure 0 0 102030405060 Time (days) 46

When making tire pressure • Note that operating pressures, Pressure loss entries in the aircraft log book, whether loaded or unloaded, it is best to record the ambient are specified for “cool” tires. Normal Response temperature along with the pressure readings. • The maximum allowable The maximum daily pressure loss for pressure loss for a tire is 5% a tire/wheel assembly is 5%. A recommended tracking system for any 24-hour period. for daily pressure checks is to The graph above shows how write tire pressure, ambient the normal pressure of a tire/wheel temperature and date on the assembly can change with time even sidewall of each tire during when no disruption in the sealing pressure monitoring. This system exists. It demonstrates method allows easy, quick follow- the importance of checking pressure up on tire pressure conditions when mounting a new assembly from line station to line station. on the aircraft.

Make sure tires have sufficient time to cool.

• A cool tire is one at ambient temperature.

• Allow 3 hours after landing, if not exposed to direct sunlight, for tires to properly cool. By carefully using the palm of the hand, it is possible to determine if a tire is cool or not. 47

Testing For Pressure Loss Check the fuse plugs or pressure Note that nitrogen will diffuse relief plugs with a soap and water through the sidewall vents for the The source of a pressure loss can best solution. If bubbles appear, entire life of an aircraft tire. be determined by applying a soap replace the valve core and solution to suspected areas of leakage recheck. Look closely for bubbles in the or by total immersion of the tire and tubewell area of the wheel to be wheel assembly in a water bath. Begin Inspect the tread and sidewall sure nitrogen is not leaking from with the most simple checks first: areas for FOD’s, cuts, snags, etc. any fatigue cracks or at the Check suspected areas with a O-Ring seal of the wheel halves. Check that the valve core is not soap solution. If bubbles appear, leaking. Apply a small amount the tire must be dismounted and If no leak source other than of soap solution on the end of repaired by a qualified repair the sidewall vents can be found, the valve stem. station or scrapped. it will be necessary to dismount If bubbles appear, replace the the tire and make a further valve core and recheck. Totally immerse the tire/wheel inspection. Be sure that the valve stem assembly in a water bath. If a threads are not damaged. water bath is not available, apply Otherwise, the valve core and the a soap or other leak detector valve cap will not fit properly. solution to the entire tire/wheel assembly. Each valve should have a valve The appearance of bubbles at any cap on it to prevent dirt, oil, point other than at the vents in moisture and other contaminants the lower sidewall of the tire just from getting inside and damaging above the wheel flange will the core. indicate a leak.

Be sure that the valve is not bent or rubbing against the wheel. If damaged, dismount the tire and replace the tube or valve. Inflation pressure maintenance

Causes of Pressure Losses An apparent pressure loss can be This condition can be caused by: caused by a drop in ambient • Insufficient inflation pressure. A tire that consistently loses inflation temperature. Was the tire • Bead toes (bias tires only) not pressure beyond the 5% daily allo- inflated in a heated room and properly lubricated. wance should be inspected to determi- stored in an unheated one? Was • Kinked or distorted beads. ne the cause of the pressure loss. Some the tire relocated from a warm • Accumulation of rubber on the inspections can be made while the climate to a cold climate? For more bead flats. assembly remains mounted on details on the effects of ambient • Dirt trapped between the tire the aircraft. Others will require the temperature, see page 42. and wheel. tire/wheel assembly to be dismounted from the aircraft and sent to the tire Use only an approved shop. Follow the guidelines given calibrated gauge, preferably of a under the section “Monitoring dial or digital type. It is best to use Inflation Pressure - What To Do.” the same gauge when monitoring a slow pressure loss in a tire/wheel There are a number of possible causes assembly. of pressure loss in a tire: Foreign object damage that Tire growth during the first penetrates the cord body and liner. 12 hours after mounting and Inspect the tire carefully for any inflation to the specified operating FOD’s. pressure. This is entirely normal. Check for improperly seated beads To avoid a possible underinflation . This condition can be condition, it is important that a tire identified by comparing the not be placed in service until it has position of the tire’s lower sidewall undergone the complete growth annular rings, mold lines, or cycle and has been reinflated to branding. Look to see if they are the specified operating pressure. uniform from side to side or that they are above the wheel flange. 49

Leaks at the valve stem wheel manufacturer, suitable Seepage between tire bead or valve core. for the intended aircraft service and wheel flange (tubeless - Put a small amount of water (in particular low temperature tires) can occur. An inspection on the end of the valve stem service) may also cause leakage should be made with particular and watch for bubbles. at the wheel mating surfaces. attention to the following: If bubbles appear, replace the core and repeat the check. • This type of leakage is very dif- • Look for exposure of cord body - Valve caps, finger tightened, ficult to diagnose since the in- in the bead toe area or bead should be used to prevent dirt service conditions causing the flat area. Exposed cords may from entering and holding open leakage are not reproducible in act as a wick for nitrogen to the valve stem. a shop. escape along. • Foreign material trapped bet- Leaks at the valve seal Leakage through the fuse plug ween the bead and wheel sea- (tubeless tires). (tubeless tires). ling surfaces causing a poor - Valve holes in the wheel must sealing between the tire and be free from scratches, gouges • Use sealing gaskets specified wheel. and foreign material. by the wheel manufacturer, • Gouges or scratches resulting - The proper O-Ring or grommet, suitable for the intended from handling or improper use as specified by the wheel aircraft service (in particular of tire irons. Damage can also manufacturer, must be used. for low temperature service). occur along the wheel half • A faulty fuse plug can allow a mating surfaces and leakage Wheel half parting line O-ring seepage of nitrogen and thus a may show in the O-ring seal seal (tubeless tires) leaks in loss of pressure. area. service. • Corrosion or wear in the bead • Twisting or failure to lubricate Pressure release plug (tubeless ledge area (usually toe area of the O-ring before installation tires). Some wheel designs have a the tire bead) will leak at the may cause leakage at the pressure release plug. The tire-wheel contact area. wheel mating surfaces. potential causes of leakage are • Use of the wrong O-Ring com- the same as for a fuse plug. pound, as specified by the Inflation pressure maintenance

In all cases, For a Mounted For a Dismounted For a Dismounted be sure Tire/Wheel Assembly, Assembly, to account for: Assembly, check tire check wheel for: check for: and tube for: Initial Stretch Period X (24 Hour Tire Growth) Changes In Air Temperature X Venting of Tubeless Tires XX Release of Trapped Air in Tube-Type Tires XX Cut or Puncture XX Damaged Beads X Improperly Seated Beads X Leaking Valve core X Other Valve Problems XX Improper Installation of O-Rings X Faulty Thermal Fuse or Installation XX Porous Wheels XX Improperly Torqued Wheel Tie Bolts X Wheel Gouges and Scratches XX Corrosion or Wear on Bead Ledge Area X Knurls X Damaged Sealing Surfaces XX Wheel Assembly Holes X 50 Wheel Cracks XX

• A tube-type wheel converted Troubleshooting - to tubeless application should Have You Considered? have the knurls removed. Leakage will show at the tire- The above pressure loss troubleshoo- wheel contact area. ting chart for tire/wheel assemblies will help you set up a uniform Leakage through the well inspection procedure which can pre- area of the wheel (tubeless tires) vent problems and speed troubles- can occur from porosity or fatigue hooting. Determine the status of cracks, particularly if fatigue life is your assembly in the columns above. exceeded. Proper painting of the wheel should seal leakage from Note: minor porosity. • Tire inflation pressure must be at operating or rated pressure Damaged Wheel Sealing when testing for points of pres- Surfaces or improperly sure loss. machined sealing surfaces may • The point of leakage can be cause slow leakage. Correct determined for the tire wheel irregularities before assembling assembly by applying a soap the wheel. Foreign material or and water solution to the entire heavy paint can impair the assembly or by immersing the sealing surface. tire/wheel assembly in water.

Damage to the tire innerliner (tubeless tires).

Small cracks or splits in the inner tube. Serviceability criteria

Tire serviceability 51 criteria Tire serviceability criteria

Tread Reinforcing plies Protector Ply Belt Plies Casing Outer Ply Casing Outer Ply

52 Wear Removal Criteria for Retreadable Bias Tire Wear Removal Criteria for Retreadable Radial Tire

A simple, easy-to-perform series of be removed from service for wear Water can affect traction: inspection procedures can prevent using the following criteria: minor incidents from developing into The accumulation of water on major problems and help to optimize Based on the fastest wearing runway surfaces can affect wet tire performance. Regular inspection location, remove tires: traction. Its affect is dependent on is a small price to pay to protect your a number of factors including water valuable tires, and the safety of your When the wear level reaches the depth, aircraft speed and runway aircraft and the people it carries. bottom of any groove along more surface conditions. The most than 1/8 of the circumference on effective method to minimize Note: If an aircraft has made an any part of the tread, the affects of water on traction is emergency or particularly to reduce water depth or allow rough landing, the tire, tube or the water to escape from under and wheel should always the footprint more rapidly. Many be checked. If either the protector ply (radial) airport authorities today have or the reinforcing ply (bias) is adopted “cross-grooving” for their On-aircraft inspection with exposed for more than 1/8 of the runway surfaces which allows tire mounted circumference at a given location. for rapid drainage of water. Note: Tires reaching this wear point Removal Criteria - Wear on an aircraft at a remote station can make a return-to- The tread area of the tire should be base flight(s) under standard visually inspected for any damage operating conditions without and the state of tread wear. Removal sacrificing retreadability of the at the right time will optimize tire wear, while still protecting the life casing. and investment of the carcass. In the absence of specific Note: In some military applications, instructions from the Airframer the removal point of a tire (Operations Manual, Service is indicated by a red fabric Bulletins, etc.), a tire should cord built into the tire or a wear depth plug. Tread Reinforcing plies Tread Reinforcing plies

Casing Outer Ply Casing Outer Ply

Normal Wear Patterns - Bias Tire Effects of Overinflation - Bias Tire

Protector Ply Belt Plies Casing Outer Ply Protector Ply Belt Plies Casing Outer Ply

Normal Wear Patterns - Radial Tire Effects of Overinflation - Radial Tire 53

Typical Wear Conditions: Overinflation When a tire has been operated Normal wear with a higher pressure When tire wear has been than required for the aircraft optimized from proper loads, an accentuated centerline maintenance and inflation wear will be apparent. pressures, the first point of Overinflation has reduced the wearout will be near the number of cycles to wearout and centerline of the tire. made the tire more susceptible Follow wear removal criteria. to bruises, cutting and shock damage. Follow wear removal criteria. Tire serviceability criteria

Tread Reinforcing plies

Casing Outer Ply Protector Ply Belt Plies Casing

Effects of Underinflation - Bias Tire

Protector Ply Belt Plies Casing Outer Ply Tread Reinforcing plies

Casing Outer Ply 54 Effects of Underinflation - Radial Tire

Underinflation Worn Beyond Recommended Flat Spotting When a tire has consistently been Limits This tire wear condition is a result operated underinflated, shoulder Tire has been worn beyond of the tire skidding without wear will result. Severe acceptable limits and into the top rotating, i.e., brake lockup or underinflation may cause ply belt plies (top carcass plies for large steer angle. separations and carcass heat bias - not shown). Tire is not build-up which can lead to retreadable. • Tire should be removed from thrown treads, sidewall fatigue service if the flat spotting and shorten tire life. Follow wear exposes the protector ply removal criteria. (radial tire) or reinforcing ply (bias tire).

• If flat spotting does not extend to the protector ply or reinforcing ply, the tire can be left in service.

• If the localized loss of rubber results in aircraft vibrations, even though no fabric has been exposed, the tire must be removed from service. Outer Ply

Worn Beyond Limits -Radial Tire

Protector Ply Belt Plies Casing Outer Ply

Asymmetrical Wear - Radial Tire

Tire Flat Spot - Bias Tire 55

Asymmetrical Wear The tire has been operated under prolonged yaw and/or camber. This camber angle can be induced through landing gear or undercarriage deformation or manufacturer’s settings/tolerances. Taxiing with one engine or high speed cornering can also cause asymmetrical wear. In some cases, low inflation pressure will contribute to this condition. Tires that do not expose any fabric can be dismounted, turned around and remounted to even up wear. As long as standard wear criteria is met, the tire should remain in service. Tire serviceability criteria

1 2

Suggested approach: 1.Tread 2.Sidewalls 3.Bead areas 56 4.Innerliner

Serviceability Criteria/ Limits Tread wear For Tire Damages * Check for typical wear patterns. When assessing tire damages, it is Follow removal guidelines given best to make inspections with the under the section “Removal tire inflated. Many damages that Criteria - Wear.” are readily visible on an inflated tire can no longer be seen when that tire is uninflated.

Be sure to mark all damages with a chalk stick before dismounting the tire.

Tires removed should be tagged with a “Reason For Removal.”

A Systematic Approach to Tire Inspection assures that all parts of the tire are properly inspected. A recommended sequence of inspection is given above: B

C A

Tread Reinforcing plies Tread Cuts Casing Outer Ply Remove tire from service Bias Tire when: A. Depth of cut exposes the casing outer

B ply (bias) or outer belt layer (radial). Embedded objects take all forms B. A tread rib C A has been severed. C. Undercutting Protector Ply Belt Plies Casing Outer Ply occurs at the base Radial Tire of any cut. 57

Tread Cuts/Foreign Objects Note: Tires removed for tread cuts Tread cut removal limits are at or other injuries should be times given in specific sent to a certified repair documentation such as aircraft station to be repaired and maintenance manuals, T.O.4T-1- retreaded or scrapped. 3, technical documentation, airline operation manuals, tire sidewall markings, etc. Follow specific guidelines when given.

In the absence of specific cut removal documentation, tires should be removed when:

• Cuts, embedded objects or other injuries expose or penetrate the casing cord body (bias) or tread belt layers (radial).

• If a cut or injury severs or extends across a tread rib, the tire should be removed from service.

• Under cutting at the base of any tread rib cut is cause for removal. Round foreign object openings are acceptable up to 9.5 mm/0.375” in diameter. Tire serviceability criteria

Bulge

Tread Reinforcing plies

Casing Outer Ply

Separations Bias Tire

Mark all cuts, foreign objects, Caution: Do not probe objects while Bulges or separations damages or leaks while tire is tire is inflated. Immediately remove the tire from inflated. Use a light colored service. Mark these areas with a crayon, wax marker or paint stick. color crayon before deflating. Damages can be difficult to find when a tire is uninflated. Chevron Cutting: Remove tire from aircraft if: • Cutting causes the tread to loosen or chunk exposing the tread reinforcing ply Chevron Cutting not exposing textile can be left in service or protector ply more than 6cm2 / 1 in2

Continue

in service if: Protector Ply Belt Plies Casing Outer Ply • Cutting penetrates the tread to a level Tread Chipping / Chunking - Radial Tire less than one- half the molded skid depth even if the surface

Tread Reinforcing plies exhibits some

Casing Outer Ply shallow chipping or Chevron Cutting - Bias Tire chunking. 59

Chevron Cutting Tread Chipping/Chunking Remove from service if the Remove from service if the chevron cutting results in reinforcing ply (bias) or protector chunking which extends to and ply (radial) is exposed for more exposes the reinforcing or than 6 cm2 / 1.0 sq. in. protector ply more than 6 cm2 / 1.0 sq. in. Tire serviceability criteria

Tread Reinforcing plies

Casing Outer Ply

Peeled Rib - Bias Tire

Tread Reinforcing plies

Casing Outer Ply

60 Cracking and Contamination - Bias Tire

Peeled Rib Note: Authorization is given Contamination Remove from service if the to return to maintenance base From Hydrocarbons reinforcing ply (bias) or protector (<6 flights) to replace tires Oil, grease, brake fluids, solvents, ply (radial) is exposed. meeting the above criteria etc. can soften or deteriorate if there is no continuous rubber components. Groove Cracking cracking exposing textile Immediately upon contact with a Remove from service if the groove greater than 25 mm / 1 inch hydrocarbon substance, wash the cracking exposes the reinforcing in length. contaminated area first with ply or the protector ply for more denatured alcohol, then with a than 6 mm/1/4” in length. Rib Undercutting soap and water solution. By Remove from service if pressing the rubber surface in the undercutting extends more than contaminated area versus the 6 mm / 1/4” under the rib. adjoining uncontaminated area, determine whether the rubber has become softened or “spongy”. If so, remove the tire from service. Abrasion & Reverted Rubber

Protector Ply Belt Plies Casing Outer Ply

Skid Burn - Radial Tire

Protector Ply Belt Plies Casing Outer Ply

Tread Splice - Radial Tire 61

Skid Burns from Hydroplaning Open Tread Splice This condition occurs on wet or Remove from service if apparent. ice-covered runways. Remove from service if the reinforcing ply or the protector ply is exposed. or if the severity of any flat spot is such that aircraft vibration is unacceptable to operational crews.

Rubber reversion visible on the surface does not affect the performance capability of the underlying tread rubber and should not be the determining factor for removal. Tire serviceability criteria

Typical Ozone cracking

Tire Cut

Extends across chine

>1/2 depth of chine Chine damage

Sidewall Bulge 62

Sidewall Cuts/Foreign Objects Sidewall Bulge/Blister/ Weather / Ozone Cracking Cuts, Snags, Gouges or Other Separation Remove from service only Injuries If any are found, the tire should if weather or ozone checking Mark all damaged areas with a be removed from service or cracking extends to the cords. light colored crayon, wax marker immediately. or paint stick while the tire is Important: Weather checking or inflated. Such injuries can be Sidewall Cut or Crack cracks that do not reach the carcass difficult to find when the tire is If condition is within the cords are not detrimental to tire uninflated. sidewall rubber, continue in performance and do not constitute service. cause for removal. Tires showing Caution: Do not probe cuts while only surface cracking can be left tire is inflated. If sidewall cords are exposed or in service. damaged, remove the tire from • If sidewall cords are exposed service. or damaged, remove the tire from service. Bulge / Blister / Separation Remove the tire from service. • Cuts in the rubber which do not reach the cord plies are not detrimental to tire performance. The tire can be left in service.

• Chine tires: Any cut that severs or extends across the chine and is more than 1/2 the depth of the chine should be removed. 63

Serviceability Criteria / Rejected Take off • Where aircraft speeds exceed Operational Conditions: Aircraft experience various levels normal landing speeds and of rejected takeoffs. Not all high braking energies are Hard Landing rejected takeoffs are severe experienced, tires should be After a particularly hard landing, enough to warrant automatic tire removed from service, labeled tires, wheels, brakes and landing removal. The following guidelines as an RTO tire and returned to gear systems should be visually are recommended: the retreader for inspection inspected for damage. and disposition. • Where aircraft speed remains below normal landing speeds Inspect the tires for any obvious and normal braking energies signs of damage such as cuts, are experienced, tires may be splits in the rubber, flat spotting, left in service. A visual inspec- tread chunking, bulges, etc. For tion should be made on each damages, follow the guidelines tire to assure all tires meet the given under Serviceability serviceability criteria. Pay par- Criteria / Limits For Tire Damages. ticular attention to any tire flat spotting that may have occur- If no damages are noted, the red as a result of braking. tire(s) should be left in service. A minimum 30 minute tire / It is recommended that an entry brake cooling period is requi- of the landing be made in the red prior to the continuation aircraft log as a future reference. of the aircraft’s flight schedule. Some tire damages, such as bottoming the tire, may not become apparent until several landings later. Tire serviceability criteria

Off-Aircraft Inspection For Bias Tires: Inspect the Tire’s Innerliner. With Tire Dismounted • An exposed chafer strip on the As with external areas, any tire bead face will normally cause A Systematic Approach with loose, frayed or broken no trouble and such a tire is fit to Tire Inspection cords inside should be for service and can be retrea- discarded. ded. A systematic approach to tire Liner blisters, especially in inspection is recommended to • Damage, blisters or separa- insure that all areas are properly tubeless tires, should be left tions of the chafer strips are undisturbed. Do not pierce, inspected. The following system is repairable. Send the tire to recommended. puncture or cut them. To do so an authorized repair station. will destroy the air-retaining • If carcass cords under chafer ability of a tubeless tire. Inspect the Tread Area. strip are damaged, the tire Follow the procedures given for should be discarded. On-Aircraft Inspections. Generally, confirm the good condition of the innerliner For Radial Tires: After the tread area, (e.g., no wrinkles). Inspect Both Sidewall Areas. • If bead area wear, along the Tube Inspection. Follow the procedures given for wheel flange, exceeds On-Aircraft Inspections. 1 mm/1/32”, remove the tire When inspecting tubes, do not from service. Inspect the Bead Areas. inflate them with more pressure than is required to simply round • If protruding bead wires, bead out the inner circumference of Check the entire bead area from wire separations, or badly kin- the tube (never more than 1 psi). just above the heel of the bead ked beads are found, the tire to the innerliner for chafing should be discarded. from the wheel flange or Carefully inspect the inflated damage from tire tools. tube for leaks. First visually and then by submersion in water. 65

Examine the valve stem for The stretch on the tube is then Inspect For Wheel Damage. leaks, signs of valve pad equalized throughout its inner separation and bent or and outer periphery. Wheels should be inspected damaged valve stems. following the wheel Also check tubes for possible manufacturer’s Inspect the tube for severe thinning out due to brake drum recommendations. wrinkles or creases. Remove heat in the area where they contact from service if any are found. the wheel and bead toes. The “set” In general, make a visual Wrinkles are evidence of or shape of the tube will help to inspection of the entire wheel. improper fitting of the tube determine when it should be Wheels that are cracked or within the tire. Where wrinkles removed from service because of damaged should be immediately exist, chafing takes place, and thinning in the bead areas. Feeling taken out of service for further that can result in loss of air or a the tube with the fingers will also checking, repair or replacement. blowout. reveal thinned areas. On wheels with only one brake If used, check the condition of Inspect tubes for evidence of drum, this heat-set condition will the thermal fuse plug or chafing by the toes of the tire normally show up only on one side overinflation plug. Melted, beads. If chafing exists, remove of the tube. In those cases where pushed out or leaking plugs the tube from service and scrap. the brake drum is a considerable should be replaced. Be sure that distance from the rim, it is unlikely sealing gaskets are the ones Examine for thinning. Where that this condition will ever be specified by the wheel the heat is greatest, the tube experienced. manufacturer for the service has a tendency to be stretched conditions of the aircraft. over the rounded edge of the Gaskets should be free from bead-seat of the wheel. This is distortion and damage. one of the reasons why, when If a fuse plug blows while the tire mounting, tubes should always is rolling, the tire and its be inflated until the tire beads axlemate should be scrapped are in position, then completely because both tire will have been deflated and reinflated to subjected to overload conditions. the final pressure. Matching / Mixability

66 Matching and mixability of dual tires 67

Matching Tires Radial tires: Mixability • Same Size In applications involving dual wheels • Same Type The mixability of aircraft tires has or dual wheels on a multi-wheel • Within the same Static Loaded become an important issue in recent landing gear configuration, tires Radius limits: years. It is Michelin’s position that should be matched in diameter the ultimate authority for approving or static loaded radius within For Civil application Radial mixability of different tires on an the appropriate association’s (T&RA, tires, use grown dimensions. aircraft lies with the aircraft ETRTO, MIL-T-5041, AIR 8505A, etc.) REFERENCES: manufacturer or aircraft design inflated dimensions for both new - “Tire and Rim Association authority who alone has full and grown tires. It is important inflated dimensions.” knowledge of all aircraft to ensure equal distribution of aircraft - “Michelin Aircraft Tire performance requirements. load on all tires and to avoid over- Engineering Databook.” loading a tire beyond its limits. A key point for mixability is that For military application matched tires carry Matching Criteria Radial tires, use inflated the same load at the same dimensions. pressure. Three possible Matching tires assures that the sizing REFERENCE: configurations of tires exist. The of the tires is such that both tires will - “Michelin Aircraft Tire following guidelines are given for carry, within industry standards, Engineering Databook.” mixability: equal loads. New versus Retreaded tires Bias - Bias Bias tires: The practice of mounting both • Bias tires can be mixed on the • Same Size new and retreaded tires on the same axle or bogie if the follo- • Same Type same axle is acceptable. Follow wing requirements are met: • Within the Overall Diameter the same guidelines as above. The tires are of the same size limits as recommended by the designation. governing association for the All tires are qualified for the particular application (civil, aircraft application. military). All tires meet the type designation and overall Matching and mixability of dual tires

OD2 OD1

SLR1 SLR2

SLR1 = SLR2 - OD1 ≠ OD2

diameter size standard aircraft testing. In all cases, loaded radius information. established by either: airframer and airworthiness - Radial tires approved for - The Tire and Rim Association authorities recommendations application on the same or must be followed. axle or bogie of an aircraft - The European Tyre and Rim will operate at the same Technical Organization Three possibilities exist: inflation pressure.

Radial - Radial 1 Bias tires on the nose gear 3 Bias tires on one main lan- • Radial tires can be mixed on and Radial tires on the ding gear bogie and Radial the same axle or bogie if the main gear or vice versa. tires on the other. following requirements are - No effect on tire or aircraft - Any proposed mixing met: performance unless must be approved by the The tires are of the same size otherwise specified by airframer. designation. the airframer. - Radial and Bias tires All tires are qualified for the approved for the same aircraft application. 2 Mixing on a gear made up application may be of All tires meet the size of bogies and dual mounts. different overall diameters standards for overall diame- - Any proposed mixing when stood side by side. ter and static loaded radius must be approved by the It is important that the established by either: airframer. static loaded radius of - The Tire and Rim Association - Radial and Bias tires the two tires be the same. or approved for the same - Radial tires approved for - The European Tyre and Rim application may be of dif- application on the same Technical Organization. ferent overall diameters aircraft but different axles when stood side by side. It or bogies may operate at Bias - Radial is important that the static different inflation pressu- • No specific rule can be applied loaded radius of the two res than the Bias tire. for this case. The mixability of tires be the same (see This is mostly true of high bias and radial tires is determi- figure above). Contact the performance military ned by the airframer through airframe manufacturer or applications. tire manufacturer for static 69

Observe Load and Inflation or in the event the tire strikes an WARNING! Aircraft tires can be Recommendations obstruction. It can cause potential operated up to or at rated inflation wheel damage. Under the severe pressure. Extremely high inflation When operating tires in strain of an extra load, the wheel pressures may cause the aircraft combination, it is important may fail even before the tire does. wheel or tire to explode or burst, to respect load and inflation which may result in serious or fatal recommendations. It is important to use inflation bodily injury. Aircraft tires must pressures recommended by the always be inflated with a properly There is a limit to the load any airframe manufacturer for each tire. regulated inflation bottle or canister. aircraft tire can safely carry. Be sure to determine if loaded or The high pressure side should never The maximum static load limits, unloaded inflation pressure is be used.The safety practices for as recommended by the Tire specified. Loaded inflation pressure mounting and dismounting and Rim Association and/or will be 4% greater than unloaded aircraft tires detailed in this Manual the European Tyre and Rim inflation pressure. must be followed. Technical Organization, are shown in the Load and Inflation Tables If tires are run at unequal pressures, in the document entitled Michelin the tire with the higher inflation Aircraft Tire Engineering Data. pressure will carry a greater share Similar information is also contained of the load even though both tires in the T&RA Yearbook and will be of the same deflection. ETRTO Data Book. This higher shared load can reduce the safety factor and service life Overloading a tire puts undue strain of the tire. on the cord body and beads of the tire, reducing its safety factor and Tire pressures should be checked service life. daily with an accurate gauge when It further increases the chance of the aircraft is engaged in more bruising, impact and flex breaks in than one flight a day. Otherwise, the sidewall or shoulder areas of the pressures should be checked tire, particularly under landing stress before each flight. Vibration / Balance

70 Vibration and balance Certain aircraft have nose landing gears which are sensitive to vibration. For these cases, assemblies should be checked for balance and wheel weights added when required. 71

Vibration, shimmy and other similar Check that the beads of the tire generally work any trapped air conditions are usually blamed on have been properly seated. out from between the tube improper tire balance. Imbalance is and tire. a well known and easily understood Check the tire for flat cause for vibration. In many cases spotting or uneven wear. Is the tube wrinkled because though, this may not be the cause. • If flat spotting does not extend of improper inflation procedures? There are a number of specific aspects to the protector ply (Radial) of the tire, wheel and gear assembly or reinforcing ply (Bias) and Is the wheel out of balance which can be the cause or contribute vibration is acceptable, the tire because of improper assembly? to aircraft vibration. As with any can be left in service. • Follow the wheel manufactu- concern, a systematic approach should rer’s instructions for properly be taken to isolating its cause. Verify that tires have been aligning wheel halves. Check that the tire has been properly mounted. • The balance mark on the tire inflated to the proper • For tubeless tires, the red should be aligned with the inflation pressure. balance mark on the lower valve mounted on the wheel, • Follow the airframer’s sidewall of the tire should be unless otherwise specified by recommendation. aligned with the wheel valve. the wheel manufacturer. • Be sure an accurate calibrated • For tube-type tires, the balance pressure gauge has been used. mark (light spot) on the lower Check the condition of the sidewall of the tire should be wheel to see if it has been bent. Check that dual tire inflation aligned with the balance mark is equalized between tires and (heavy spot) on the tube. Check for a loose wheel per the operating specification. bearing caused by an Check for air trapped improperly torqued axle nut. Assure that the tire reached between the tire and tube. full growth before it was • Use a soapy solution to check Check for poor gear alignment installed on the aircraft. for leakage at the base of the as evidenced by uneven wear. • Allow at least 12 hours at tube valve stem where it exits operating or rated pressure for the wheel. Check for worn or loose the tire to attain full growth. • Rolling the tire by taxiing will landing gear components. Dismounting

72 General dismounting instructions for aircraft tires 73

Removal from landing gear It is further recommended that Tire dismounting removal information accompany Deflate any non-serviceable, damaged the tire to the repair station or Proper dismounting procedures tire/wheel assembly before dismounting retreader. The simplest approach is simplify the job of servicing aircraft from the aircraft.Worn, serviceable to use a tag or label attached to the tires, while increasing safety and units may be left inflated. tire with a self sticking adhesive reducing the chances of damaging (applied to lower sidewall) or by use tires or wheels. The task of Reason for removal - Tracking of heavy or nylon string. dismounting tires should not be undertaken without proper In order to properly track reasons for Caution: Do not use staples equipment, instructions and trained tire removal and to take appropriate or other metal devices for affixing personnel. action, it is very important to have tags or labels to tires or inner tubes. accurate information regarding tire Keep adhesive labels above the bead Careful attention must be given to removal.This information helps the area of the tire. disassembling and handling wheel retreader or repair station to make components to avoid damage to decisions concerning inspections and A sample label is shown above. critical surfaces. To assist in this the future use of the tire. process, wheel manufacturers Recommended information publish specific instructions in their includes: maintenance and overhaul manuals. Follow their recommendations and • Name of Operator procedures to assure trouble-free dismounting. • Date of dismounting • Aircraft model tail number • Tire part number • Tire serial number • Reason for removal • Number of tire landings General dismounting instructions for aircraft tires

TIRE

RING

WHEEL

Bead roll-over

Tire/Wheel Dismounting Completely deflate the tire • Ensure the faces of the adaptor Sequence or tube before dismounting. rings or press pads, in contact • Use caution when unscrewing with the tire, are free of nicks, The same methods are essentially used valve cores. burrs or sharp edges which for dismounting tubeless bias, tube- The pressure within the tire or could damage the tire surfaces. type bias and radial aircraft tires. tube can cause a valve core to However, radial tires have a smaller be ejected at high speed. Apply bead breaker ram bead flat area and have a more • If damage has occurred, a pressure or arm pressure flexible sidewall, which requires that tire/wheel assembly should be slowly or in a series of more attention be placed on the deflated in a protective cage. sequences or jogs to allow time tooling set-up. Failure to use proper for the tire’s beads to slide on tooling designed for the particular tire Use a bead breaker to loosen the wheel. size could result in dismounting tire beads from both wheel-half • Because of the flexible side- difficulties. Follow the tooling flanges. walls of a radial, use of incor- guidelines given in the next section. • Always use proper bead breaking rect tooling or applying pres- equipment designed for separa- sure too rapidly can cause Once tooling has been set-up, ting tires from wheel bead seats. sidewall distortion. Heavy dis- dismounting should occur in a Do not use pry bars, tire irons, tortion of the sidewall is not similar manner for both bias and or any other sharp tools to only harmful to the internal radial tires, tubeless and tube-type. loosen tire beads. Damage tire components, but it may Before beginning any tire to the tire and wheel may occur. also begin to “roll” the beads, making dismounting more dif- dismount, be sure to follow the • Do not loosen wheel tie bolts prior to breaking the beads ficult. instructions and precautions loose. Damage to the mating published in the wheel surfaces of the wheel halves supplier’s maintenance manual. can occur. Mark damaged or bulge areas • Ensure that the adaptor rings before deflating, using a of the ring type bead breaker contrasting color chalk. have passed over the wheel flanges and do not interfere with any wheel components. 4" (100 mm) TRAVEL

FIXED ADAPTOR RING 0.4” (10 mm) RADIAL CLEARANCE

RAM

MOVABLE ADAPTOR RING Ring-type bead breaker

What To Do If The Tire procedure following the same Tire Dismounting Equipment Becomes Fixed To The Wheel procedure. If a tire bead rolls such that it will The primary component for no longer slide on the wheel: Note: Cases of bead roll over should dismounting an aircraft tire from its be reported to the retreader wheel is the bead breaking equipment • Release ram pressure. who will examine the tire for used to loosen the tire from the wheel Apply a soap solution to damage. A tire found to have bead seats. the tire/wheel interface. been damaged should be Allow several minutes for the scrapped. Two types of bead breaking solution to penetrate between equipment can be identified here: the tire and wheel. Remove tie bolts and slide out both parts of the wheel from The “ring” type bead breaker. Note: Do not use hydrocarbon-based the tire. Bead breaking is performed by lubricants. These can be harm- pushing a movable adapter ring ful to the rubber components For tube-type tires, remove the against the lower sidewall of of the tire. tube. one side of the tire. The opposite side consists of a • Reapply a reduced hydraulic Tire is now dismounted. stationary adapter ring that also pressure to the tire. contacts the lower sidewall of • Repeat several times if neces- the tire. sary. It is important that the “adaptor” If the tire still remains fast: rings be designed for the particular tire/wheel assembly to be dismounted. • Remove the tire/wheel assembly from the machine. The optimum condition is an • Reinflate the tire in a cage adapter ring internal diameter until the bead moves back to as close to the wheel flange its correct position. diameter as possible. Pushing • Deflate the tire. too high on the tire sidewall will • Recommence the dismounting General dismounting instructions for aircraft tires

PRESS ARMS

PRESS PADS

76 Pincher-type bead breaker

only distort the sidewall and Localized “pincher” type bead Note: When pressing against the bead area, making dismounting breaker. tire, hold the pressure for more difficult. 1-2 seconds to allow the bead This equipment consists of two time to move. Bead breaking For practical purposes, a radial press arms which can be is most efficient when the clearance between the tip of the operated in a “pincher” tire/wheel assembly is rotated wheel flange and the internal movement. At the end of each approximately 30 degrees bet- diameter of the adaptor ring is arm is a press pad in the form ween each pressing necessary to avoid interference of a sector. An adjustable operation. between the wheel and adaptor cylinder is used to position the ring as it approaches and tire so that the sectors can be The press pads used to push travels over the wheel flange. matched to the size of the tire. the tire are “universal” and are designed to push on the tire Michelin recommends a radial The tire/wheel assembly is close to the wheel flange. No clearance of 0.4 inches (10 mm). positioned such that the press specific tooling is required for pads contact the tire’s lower the different tire sizes to be The movement (travel) of the sidewall just above the wheel handled. adaptor ring should be at least flange. four (4) inches (100 mm) to ensure complete separation of Pressure is applied to break the the tire from the wheel. beads. After the first sector of the tire begins to move away It is desirable that the rings be from the wheel flange, stop, designed such that the tire can rotate the tire/wheel assembly a be observed while pressure is short distance and repeat the being applied, to ensure operation until all sectors of the satisfactory ring contact and tire are loose and free from the progress. wheel. Retread / Repair

Retreading and repairing 77 aircraft tires Retreading and repairing aircraft tires

Many aircraft tires that become Retreading Aircraft Tires Inspections must meet approved injured in service can be successfully process limitations for that tire to be repaired.Tires of which the treads are For aircraft tires, the term retreaded. worn out, flat spotted, or otherwise “retreading” refers to the methods of damaged, but of which the cord body restoring a used retreadable tire by Repairing Aircraft Tires is intact, can be retreaded. Retreading renewing the tread alone or by and repairing aircraft tires has been a renewing the tread plus the Many tires with injuries or damages can common practice for many years and reinforcing ply(s) or protector ply. be repaired at the time of retreading can save aircraft operators and put back into useful/safe service. considerable sums of money. Full recapping is the recommended Injuries must be within the Tires that might otherwise have been procedure for tires with evenly worn manufacturer’s repairable limits. discarded due to insufficient or tread, tires with flat-spotted tread, or damaged tread can be retreaded or tires with numerous cuts in the tread Tires with sidewall cuts, snags, scuffs repaired for continued service, at a and cracking from ozone can remain cost much lower than that of a new area. The new tread material extends in service if the carcass ply is not tire. Retreading and repairing extends around and over the shoulder of the exposed. Damages that expose the service life of a carcass several tire for several inches. carcass textile can be repaired by an times past initial new tire usage. Accepting Tires for Retreading approved repair station if the cords FAA/JAA Regulations require are not cut or damaged. retreading and/or repairing of aircraft Accepting tires for retreading Note: Repairable limits generally tires to be performed in certified requires careful inspection of all exceed service-ability limits retread and repair stations by or components of the tire. Each used to remove tires from ser- under the responsibility of individual tire is inspected by visual qualified/certified technicians. Repairs and air needle techniques prior to, vice. Detailed, safe inspections by unauthorized sources are not during, and after the retreading suitable for determining the recommended. process. Shearography inspection gravity of an injury cannot be can also be used to inspect for made on inflated, mounted Michelin meets or exceeds all testing internal defects which may limit the tires. Service removal limits requirements of the FAA or JAA retreadability of a carcass. are further set to ensure safe for retreaded aircraft tires. operation and retreadability of the casing. 79

Non-repairable aircraft tires Repairable aircraft tires Sidewall Rubber Surface defects on large The following list outlines some of The following are acceptable when commercial tires may be the conditions which can disqualify retreading aircraft tires: repaired provided the repair is a tire from being retreaded: Tread Area at least 1 inch from the bead Any injuries to the beads or in The size of cuts and/or other heel, and no greater than an the bead area (except injuries tread injuries that can be area 11/2 inches (50 mm) by limited to the bead cover or repaired during retreading is 4 inches (100 mm), and does finishing strip). dependent on many factors, not penetrate or damage the Weather checking or ozone including the injury’s length, carcass ply. cracking of tread orsidewall that depth and width as related to results in exposed body cords. the tire size itself. The number Protruding bead wire or kinked and size of a repairable injury is bead. also dependent on the Ply separation. retreader’s repair methods and Internal damage or broken cords. validation. If specific details on Flat spots and skid burns that repair limits are needed, see have penetrated to the top your Michelin retreader. carcass ply. Wearing the tire beyond the protector ply or Bead Area reinforcing plies can leave Minor injuries to the bead area insufficient interface rubber to may be repaired provided the allow retreading. carcass plies are not damaged. Punctures that penetrate the innerliner. Innerliner Excessive brake heat damage, Innerliner surface damage may such as that experienced in an be repaired (bias tires). The size of aircraft rejected takeoff. a repairable injury is dependent Tires that are heavily oil soaked. on the retreader’s repair methods Tires that have experienced a as well as government regulatory major pressure loss. documentation. Operating tips

80 Operating and handling tips for better tire service 81

Optimized tire performance is directly a scuffing action along the outer influencing heat buildup. A taxi related to the use and care the tire is edges of the tread and results in speed of 40 mph for 35,000 feet is given.While the single most important more rapid wear. demonstrated during the TSO action for obtaining optimum tire certification of a tire. performance is a program of regular If an aircraft tire strikes a chuckhole, For either speeds or taxi distances tire inflation maintenance, user (pilot) stone, or some foreign object lying greater than these limits, a 5-10 minute actions and the condition of the on the runway, taxi strip or ramp, pause is recommended before airport surfaces are also important. there is more possibility of it being takeoff. The following information is to help cut, snagged or bruised because of bring an awareness of these important the high operational deflection. For less foreign object damage in factors which can further your tire If one of the main landing gear taxiing, all personnel should make investment. wheels, when making a turn, drops sure that ramps, parking areas, taxi Taxiing off the edge of the paved surface, strips, runways and other paved this may result in severe sidewall or surfaces are regularly cleaned and shoulder damage. The same type of cleared of all objects that might Unnecessary tire damage and damage may also occur when the cause tire damage. excessive wear can be prevented by tire rolls back up over the edge of the proper handling of the aircraft pavement. Pivoting By Using Brakes during taxiing. With dual main landing gear wheels, Increased airport traffic and longer Most of the gross weight of any it is important that they equally taxi runs are subjecting tires to more aircraft is borne by the main landing share the weight carried by that abrasion from turning and pivoting gear which may consist of two, four, landing gear assembly. while braking. eight, or more tires. The tires are designed and inflated to absorb the As airports grow in size, and taxi Severe use of brakes under pivoting shock of landing and will normally runs become longer, chances for tire conditions can wear flat spots on deflect about three times more than damage and wear increase. Internal tires and cause them to become out a passenger car or truck tire. The tire heat buildup also can be of of balance, making premature greater deflection allows the tire to concern. Speed, length of rolling and retreading or replacement necessary. carry the heavy loads. It also causes stops are all important in Pivoting on surfaces with heavy more working of the tread, produces texture or a step condition can Operating and handling tips for better tire service

locally tear the tread from the Chuckholes, pavement cracks or step- Immediately upon contact with a casing. This tear may not show as a offs in the pavement can all cause tire hydrocarbon substance, wash the separation until later in the tire’s damage. In cold climates, especially contaminated area first with service life. during winter, all pavement breaks denatured alcohol then with a soap should be repaired immediately. and water solution. If the rubber Careful pivoting of an aircraft also feels soft or spongy when probed, helps prolong tire tread life. When an Accumulated debris on paved areas, remove the tire from service. aircraft is turned by locking one including hangar floors, is especially wheel (or wheels), the tire is hazardous. Stones and other foreign Nylon Flat Spotting scrubbed, with great force, against material should be kept swept off all the pavement. A small rock or debris paved areas. Special attention should Nylon aircraft tires will develop flat that would ordinarily cause no be paid to make sure that tools, bolts, spots under static load. The degree of damage can virtually be screwed screws, rivets and other repair this flat-spotting will vary according to: into the tire. This scuffing and materials are not left lying on an grinding action takes off tread aircraft so that when it is moved, they the temperature of the tire rubber and places a very severe fall to the floor. If a tire rolls over such when the aircraft is first parked, strain on the sidewalls and bead material it can result in punctures, cuts the pressure in the tire, areas of the tire at the same time. or complete failure of the tire and tube. the load being applied to the Making wide radius turns will reduce tire while the aircraft is parked, tread rubber removal and sidewall Avoid Chemical Contamination the ambient temperature, stresses. the length of time the tire is Chemicals and hydrocarbons such subject to a combination of the Condition of Airport Field as jet fuel, hydraulic fluids, grease, above conditions, cleaning agents, etc., can damage the type of construction (under Regardless of preventive maintenance aircraft tires by softening or similar conditions, a radial tire and the care taken by pilot and deteriorating the rubber surface. will develop less flat spotting ground crew, tire damage is almost During aircraft maintenance, tires than will a bias tire). certain to result if runways, taxi strips, should be covered to protect them ramps and other paved field areas are from accidental spills. Keep runway On a practical level, aircraft in bad condition, strewn with debris surfaces clean so that tires are not maintenance personnel cannot or poorly maintained. parked in surface puddles. influence all of these variables. 83

To minimize the condition, inflation can cause chevron-type cutting of the occurs. This action is usually referred pressures should be kept at their tire tread ribs, particularly on the high to as “dynamic hydroplaning.” Its specified operating levels and loads pressure tires used on jet aircraft. occurrence is a function of water held to a minimum during the static depth and aircraft speeds. load period. Chevron cutting occurs during aircraft touchdown at “spin-up”. As the tire The same phenomenon can result Under normal conditions, a flat spot begins to accept aircraft loads, when a thin film of water on the will disappear by the end of the taxi it deforms slightly in these cross- runway mixes with the contaminants run. In the unusual case where deep grooves. At the same time rapid present or if the surface texture of the flat-spotting has occurred, additional acceleration is occurring. The forces runway is smooth. This is called taxiing is recommended prior required to accelerate the tire to “viscous hydroplaning.” Generally to take-off. ground speed cause a tearing action the irregular condition of the runway which forms the chevron. surface is sufficient to break up An aircraft that is to remain idle for a this film. period longer than three days should These cuts are at right angles to the either be moved every 72 hours or ribs and rarely penetrate to the fabric Today, most airport runways are blocked up so that no weight is on the tread reinforcement ply or protector designed to minimize water buildup. tires. Aircraft in storage (out of service ply. Refer to the section on “Tire Cross-grooving is one example. In for more than 14 days) should be Serviceability Criteria” for handling addition, tires have circumferential blocked up so that there is no weight this condition. grooves which help to dissipate water. on the tires. Hydroplaning An aircraft tire experiencing Chevron Cutting hydroplaning (usually viscous This condition results when, on a wet hydroplaning) may form an area of Cross-cutting of runways is common runway, the tire’s tread is progressively reverted rubber or skid burn in the at many major airports around the lifted off the runway surface. A wave tread. This area will be oval in shape world. It improves drainage, reduces of water builds up in front of a rolling similar to a flat spot. If the reinforcing the danger of standing water and tire, allowing the tire to ride on the ply or protector ply is not exposed, thus, decreases the risk of water and lose contact with the the tire can remain in service. hydroplaning. However, the sharp- runway surface. Loss of traction, edged ridges of concrete that result steering ability and braking action Operating and handling tips for better tire service

Note: A similar reverted rubber tread condition can occur if the tire slides on ice for any distance.

Tire removal criteria should be based on operational and tire condition factors. Factors to be considered are: runway cross-grooving, tire footprint area (number and remaining depth of grooves), and level of runway flooding. When operational and tire condition factors are conducive to hydroplaning, removal criteria should be adjusted accordingly. Contact Michelin for detailed information. Landings per tread

Tire performance can be improved by using slow taxi speeds and by letting the aircraft roll during landing and by avoiding hard braking. Whenever possible, make large radius turns which minimize tire scrubbing. Design: • Michelin Aircraft Product Line • Studio graphique Michelin • Gris souris

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Headquarters Research & Retread Service

Michelin Aircraft Tyre Development Centers 23, place des Carmes-Déchaux Charlotte - U.S.A. Bourges - France 63040 Clermont-Ferrand Cedex 9 - France Greenville - U.S.A. Cuneo - Italy Studio graphique Michelin Tel: 33 (0)4 73 32 76 40 - Fax: 33 (0)4 73 32 76 42 Ladoux - France Kansas City - U.S.A. Nong Khae - Thailand Commercial Offices Norwood - U.S.A.

North, Central and South America : Michelin Aircraft Tire Corporation Manufacturing 1305 Perimeter Road Plants Greenville, SC 29605 - United States Bourges - France Tel: 1 864 422 7000 - Fax: 1 864 422 7071 Nong Khae - Thailand Europe, Middle East and Africa: Norwood - U.S.A. Michelin Aircraft Tyre 23, place des Carmes-Déchaux 63040 Clermont-Ferrand Cedex 9 - France Tel: 33 (0)4 73 32 76 36 - Fax: 33 (0)4 73 32 76 44 www.michelin.com/aviation Far East and Oceania: Michelin Aircraft Tyre Asia SPE Tower 12th Floor 252 Phaholyothin Road Samsaen Nai, Payathai Bangkok 10400 - Thailand Tel: (66 2) 619-3530 - Fax: (66 2) 619-3069 Reference: #MAT-CSM-01 Rev.A Rev.A #MAT-CSM-01 Reference: