Aviation Mechanics Bulletin May-June 1999

FLIGHT SAFETY FOUNDATION Aviation Mechanics Bulletin MAYÐJUNE 1999 Managing Aircraft-tire Wear and Damage Requires Adherence to Removal Limits FLIGHT SAFETY FOUNDATION Aviation Mechanics Bulletin Dedicated to the aviation mechanic whose knowledge, craftsmanship and integrity form the core of air safety. Robert A. Feeler, editorial coordinator MayÐJune 1999 Vol. 47 No. 3

Managing Aircraft-tire Wear and Damage Requires Adherence to Removal Limits ...... 1 Maintenance Alerts...... 13 News & Tips ...... 16

AVIATION MECHANICS BULLETIN Copyright © 1999 FLIGHT SAFETY FOUNDATION INC. ISSN 0005-2140 Suggestions and opinions expressed in FSF publications belong to the author(s) and are not necessarily endorsed by Flight Safety Foundation. Content is not intended to take the place of information in company policy handbooks and equipment manuals, or to supersede government regulations. Staff: Roger Rozelle, director of publications; Mark Lacagnina, senior editor; Wayne Rosenkrans, senior editor; John D. Green, copyeditor; Karen K. Ehrlich, production coordinator; Ann L. Mullikin, production designer; Susan D. Reed, production specialist; and David Grzelecki, librarian, Jerry Lederer Aviation Safety Library. Subscriptions: US$35 (U.S.-Canada-Mexico), US$40 Air Mail (all other countries), six issues yearly. ¥ Include old and new addresses when requesting address change. ¥ Flight Safety Foundation, 601 Madison Street, Suite 300, Alexandria, VA 22314 U.S. ¥ Telephone: +1(703) 739-6700 ¥ Fax: +1(703) 739-6708

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FSF Editorial Staff

Aircraft tire/wheel-assembly failures anticipate the use of products from involve various operational and main- different tire manufacturers. The tenance factors, but detectable dam- procedures are written to comply age to one or more tires sometimes is with applicable regulations and safe the underlying cause. Such failures practices developed by airframe, occur infrequently; nevertheless, cor- wheel and tire manufacturers. When- rectly maintaining tire components — ever the safety of a tire is in question, whether in a new tire or a retreaded the tire should be removed from ser- tire — helps ensure that tire/wheel vice and should be sent to a certified assemblies will perform reliably un- repair-and-retread station for further der high static loads and dynamic inspection and disposition. loads. The airframe manufacturer’s procedures typically specify limits for For most tire anomalies, a consensus wear and damage. based on experience and testing in the aviation industry guides an appropri- Airlines typically establish tire- ate response or a range of appropriate maintenance procedures that responses. Separation of plies and tread or tire bulges, for example, sure that at least one of the signatories require immediate removal of the tire was signing for someone else’s work. from service. Nevertheless, differences (CHIRP note: This incident was inves- in perception or in the evaluation tigated by the airline and the tire was, criteria applied by flight crews and in fact, serviceable, with two millime- maintenance crews sometimes gener- ters [(mm); 0.079 inch] of tread re- ate questions about airworthiness, as maining over more than 75 percent of shown in the following incident report. the tire. The ‘cuts’ referred to by the reporter were ozone-induced cracks The report to the U.K. Confidential and were acceptable. The airline has Human Factors Incident Reporting since issued [tire-tread] depth gauges Program (CHIRP) in 1998 said, “Dur- to be used on this [aircraft] type).”1 ing completion of the exterior inspection prior to departure, I noticed that The report shows that some anoma- the right nose-wheel tire [of a Boeing lies in tire/wheel assemblies are “ac- 777] was bald with several cuts down ceptable conditions” and are not to and, in one case, through the tire cause for removal of the tire from cords. An inspection of the technical service. Maintenance technicians log shows that the [extended-range must communicate clearly the ap- twin-engine operations (ETOPS) pre- proved tire-maintenance procedures departure check], transit [predeparture and the applicable wear limits or check] and ramp check had been damage limits in a given situation. signed off as satisfactory. A verbal For example, spiral wrap — the rein- question to the ground engineer as to forcing cords wound into the tread of the serviceability of the nose wheel some retreaded tires to reduce chev- received the response, ‘Oh, that’s OK ron cutting and tread chunking — for lots more landings.’ Only when I typically begins to show as a tire entered a defect in the tech log to wears, but the appearance of these the effect of ‘Please confirm service- cords does not compromise safety. ability of right nose wheel’ [was] a (See “Limits for Tire Damage Also wheel change … called for. It was then Involve Common Principles” on page apparent that … nose wheels were out 9 for a discussion of chevron cutting of stock and that one needed to be and tread chunking.) obtained from an outside contractor. A two-hour delay resulted. I am sure Deviations from approved tire- that commercial pressure played a maintenance practices — including as- strong part in the attempt to dispatch sessment of wear and damage — have the aircraft in this state. But two peo- potentially serious consequences. Sep- ple had to sign the relevant checks and aration of tires and tire treads from tire/ inspections in the tech log, and I am wheel assemblies has been cited as a

2 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 causal factor in some accidents and although the tire remained in- incidents. Typically, the reports do not flated throughout the landing. say whether the underlying damage or Half of the right gear-leg door wear could have been detected prior had been torn off, and the in- to the event.2 Nevertheless, one typi- board flap assembly was dented. cal consequence with adverse safety A falsework [access] panel on implications has been tire-tread delam- the wing undersurface was also ination on takeoff, with various de- damaged, and the inboard grees of foreign-object damage to ground spoiler had a 10-inch aircraft engines, control surfaces and [25-centimeter (cm)] hole in the other components. trailing edge. The tire, which was on its second retread, failed af- The accident and incident reporting ter 236 landings. Examination of system (ADREP) maintained by the the tire tread indicated a number International Civil Aviation Organi- of cuts consistent with the tire zation (ICAO) contained the follow- having run over a foreign object. ing events involving various types of It was not possible to establish damage that originated in one or more where or when the tire had suf- tires: fered the damage, which led to the tread failure, although it was ¥ The report for a March 1992 in- likely to have been within the last cident involving a tire failure on one or two departures.” a Boeing 737-400 during takeoff from Milan, Italy, said, “On ¥ The report of a June 1990 inci-

takeoff, just after V1, the pilot felt dent involving a tire failure on a a slight bump. The crew were McDonnell Douglas DC-9-50 unaware of any damage until the during takeoff from Atlanta, [air traffic] controller advised Georgia, U.S., said, “During them of debris on the runway and takeoff, the no. 4 tire blew. The a passenger reported damage to aircraft returned and landed safe- the right wing. The pilot rea- ly. Damage to the [tire] inner soned that the right main gear liner consistent with underinfla- had suffered tire damage and tion was found. The maintenance diverted to [London Stansted program for the operator re- Airport, England]. A tendency to quired tire pressure to be checked roll to the right dictated a 30- with a gauge during layover in- degree flap landing, but a safe spections. The inspection was landing was made. The tread of done the previous day. Recap the right outboard main-wheel records revealed that the tire was tire had separated completely, recapped and delivered to the

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 3 operator with a pinhole in the lin- noise. The pilot aborted the take- er which allowed a slow leak. off. Pieces of rubber from [the] The pinhole was not repaired no. 3 tire were found in [the] before delivery to the operator.” no. 2 engine. The engine fan was destroyed, and several … guide ¥ The report for a July 1996 inci- vanes were damaged.” dent involving failures of six tires on a Tupolev Tu-154M/Tu-164 A report to CHIRP in 1998 showed during takeoff from Delhi, India, the value of careful observation said: “During the takeoff run, as throughout the tire-maintenance pro- the aircraft accelerated through cess. The report said, “Due to an acute about 150 kilometers per hour shortage of certifying engineers, I [81 knots], the crew heard a found myself working a ‘ghoster’ ‘bang,’ and the aircraft began to [working a night shift immediately veer to the right. The takeoff was after a day shift]. During the daily aborted, and the aircraft [was] inspection on a nightstop aircraft [an brought to a safe stop on the run- aircraft left overnight] the no. 1 main- way. It was subsequently dis- wheel tire was found to be ‘worn to covered that four tires on the limits.’ The main wheel was replaced right main undercarriage and two by myself and the paperwork com- [tires] on the nose had failed. The pleted. A mechanic then took the accident happened in darkness unserviceable wheel to the goods out- (0010 local time) but in visual wards area. It was then that he no- meteorological conditions [with] ticed a locking spacer still attached temperature 28 degrees Celsius to the unserviceable item, which [(C); 82 degrees Fahrenheit(F)]. should have been transferred to the … The tire failure is said to have replacement wheel. The situation was been caused by the allegedly quickly rectified with the spacer be- poor condition of the runway ing fitted to the aircraft. If the spacer coupled with the premature ag- had not been fitted, the main wheel ing of the tires due to the aircraft would have been free to move along being parked at Delhi for long the axle and disengage from one of periods in excess of 40 degrees the rotors on the brake pack. I had not C [104 degrees F].” noticed my error, and, with hindsight, ¥ The report for an August 1997 was too fatigued to safely certify the incident involving a tire failure task and the aircraft.”3 on an Airbus A300 during takeoff from Los Angeles, California, Criteria for judging aircraft-tire U.S., said, “During takeoff at wear and damage vary among 145 knots, the crew heard a loud civil aviation authorities, airframe

4 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 manufacturers, tire manufacturers and assembly in service. Some specialists airlines. Nevertheless, several princi- recommend approaching tires from ples are universally applicable, with an oblique angle in the direction of regular preflight inspection as the foun- the tire’s shoulder (the edge where the dation. Many airlines and regulatory tread meets the sidewall). Other au- authorities consider daily inspection of thorities recommend approaching in tires — including checks of pressure the direction of the tire tread; that is, with calibrated gauges — essential for not in the direction of the sidewall. safe operation. Visual inspection of tire/wheel assemblies after every land- Some forms of damage are insidious ing or at every turnaround also is because they are difficult to detect recommended as a good practice. visually or develop slowly with no symptoms. For example, long-term Successful tire maintenance requires operation of tire/wheel assemblies at adherence to a program that includes less than specified operating pressure not only the regular-interval checks gradually weakens tires; use of and preflight inspections, but also thor- greater-than-normal braking energy ough inspections of demounted tires may cause internal structural damage (and tubes, if applicable). Policies and to tires; and the effects of bottoming procedures also should specify how a tire (wheel flange contact with the tire/wheel assemblies will be removed runway) on landing may not become from aircraft and inspected following apparent until symptoms appear abnormal events such as rejected take- several landings later. offs, hard landings, excessive brake- heat generation or failure of the other Tires should remain mounted and in- tire/wheel assembly on that axle. Dis- flated, however, until inspections have position of tires based on such been completed and suspected dam- inspections should be explicit, and age areas have been marked with a compliance should be documented. chalk stick, light-colored crayon, wax marker or paint stick, and the reason Safety procedures for all inspections for removal from service has been of tire wear and tire damage should written on a tag attached to the tire. be followed carefully and consistently. A tire/wheel assembly that obvi- ously has been damaged, for example, Normal-wear Baseline should be deflated by a remote means Simplifies Problem after cooling for at least three hours. Detection Maintenance technicians also should follow approved safety instructions Aircraft manufacturers, regulatory au- for approaching any tire/wheel thorities, tire manufacturers, operators

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 5 and various engineering-standards and removal of the tire from service. technical organizations issue proce- Bulges often indicate cord-body dures, criteria, photographs and other damage, or internal separation of tools for systematically judging wheth- tread or plies. Areas that show er or not any wear limits or limits of bulges must be marked careful- tire damage have been exceeded. ly before deflating the tire to en- able identification later; The following principles concerning ¥ If the fuse plug of a tire/wheel tire wear and damage generally ap- assembly melts and releases ni- ply to aircraft tire/wheel assemblies, trogen while a tire is rolling, but aircraft maintenance manuals, some procedures require the tire component maintenance manuals and its axle mate to be tagged and technical bulletins should be con- immediately as unsuitable for sulted for any specific aircraft: further service and discarded; ¥ All tires (and tubes, if used) ¥ Any rub marks on tires, gear or should be inspected immediate- wheel wells require verification ly after delivery by qualified tire- of adequate clearance for the tire/ shop personnel for damage from wheel assembly; shipping, handling or storage. Such damage could include cuts, ¥ Hydrocarbon contaminants tears or foreign objects penetrat- should be removed from the ing the rubber; cuts, contamina- tire according to specifications, tion or wrinkling of the inner then possible damage should be liner; bulges and permanent assessed by pressing the contam- deformations; debris or cuts on inated area to detect abnormal the bead seating surfaces; bead texture (sponginess or softening). distortions; cracking that reach- Such damage warrants removal of es cords; and rubber-attacking the tire from service. contaminants (especially hydrocarbon products such as fuel, oil, Limits for Tread Wear grease, brake fluid or solvents) Emphasize Variation that can cause visible blisters or From Expected Patterns swelling. Appropriate tables of limits for cut length and cut Tread depth on aircraft tires affects depth should be consulted to de- contact with runways and taxiways termine whether a cut or crack is similar to the way automobile tires acceptable; “grip the road.” Tread grooves also ¥ A bulge in the tread or sidewall must be deep enough for water to pass typically warrants immediate under the tires, minimizing the risk

6 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 of skidding or hydroplaning on wet expose more than a specified amount runways. Inspections usually include of tread-reinforcing ply (bias tire) or descriptive visual criteria and wear protector ply (radial tire) to keep a values that can be measured with a tire in service. Assessment of damage, tread-depth gauge — typically cali- however, may include detailed crite- brated in thirty-secondths of an inch ria for measurement of penetration. and/or in millimeters — according to manufacturers’ specifications. Criteria for measuring and evaluating tire wear should be obtained from A basic principle of tire inspection is the airframe manufacturer’s aircraft that the tread should show a normal operations manual, aircraft mainte- wear pattern, which is relatively even nance manual, service bulletins and over time. Achieving this requires similar approved documents for the strict use of specified operational in- specific aircraft. Among other topics, flation pressures and consistent main- the aircraft operations manual typi- tenance practices. In normal wear, the cally specifies whether return-to-base wear limits are reached first along the flights are permitted if tires reach centerline of the tire tread. Accentuat- specified wear limits on an aircraft at ed centerline wear is the typical symp- a remote location, and under what tom of overinflation. Accentuated operating conditions. More conserva- shoulder wear is the typical symptom tive wear limits might be specified for of underinflation. Correct balancing of aircraft operating conditions that the tire/wheel assembly also is impor- could cause hydroplaning. tant. Imbalance can cause severe vibration and irregular tread wear. One major manufacturer, for example, recommends the following wear- During normal wear of a retreadable removal criteria for the company’s bias-ply tire, gradual removal of tread products based on examination of the first exposes the tread-reinforcing ply. fastest-wearing area along the tread:4 Beneath this ply is the undertread lay- ¥ The wear limit for nonretread- er, and beneath that layer are carcass able tires is the first appearance plies. During normal wear of a retread- of casing cords (any amount of able radial tire, gradual removal of exposed casing-cord area) for tread first exposes the protector ply. Be- bias-ply tires or the first ap- neath this ply is the undertread layer, pearance of belt-ply cords (any followed by belt plies and carcass plies. amount of exposed belt-ply cord area) for radial tires; and, For both types of tire construction, tread-wear criteria for retreadable ¥ Retreadable tires should be re- tires typically cite that wear must not moved from service before the

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 7 wear exceeds the retreadable from misadjustment of landing limit. This limit is when the wear gear, poor taxi technique or oth- level reaches the bottom of any er reasons — sometimes can be tread groove along more than corrected by reversing the tire’s one-eighth of the circumference position on the wheel. on any part of the tread, or the tread-reinforcing ply of a bias- Another tire manufacturer said that a ply tire or the protector ply of a tire should be removed from service radial tire is exposed for more when the tread has worn to the base than one-eighth of the circumfer- of any groove at any spot, or to a ence at a given location. depth shown in the aircraft maintenance manual. Another general rule The following special types of tread is that tires worn to fabric in the wear also have limits: tread area should be removed from service regardless of the amount of ¥ Tread-rubber reversion, skid burn tread remaining.5 and flat spotting (typically oval areas where abrasion and exces- Most tires used by airlines are sive heat generation have convert- designed for a service life encom- ed tread rubber to the uncured passing multiple remanufacturing (re- state or caused localized tread- treading) cycles because the tire-cord rubber loss) occur for several rea- bodies wear more slowly than treads sons, such as when a brake lockup in normal operations. Control of qual- occurs or the aircraft skids on a ity and safety is performed under the wet or ice-covered runway. Tire regulations of applicable airworthi- manufacturers specify criteria for ness authorities. Some authorities evaluating this type of wear, such specify a maximum number of re- as whether a specified amount of tread cycles. Others rely on approved cord-ply fabric has been exposed. programs in which certified techni- For flat spotting, for example, one cians consult records and use quality- manufacturer recommends con- control tests to determine when any tinued use of the tire except when tire-cord body exceeds safety limits the worn area exposes any of the for further retreading. In the United reinforcing ply of a bias-ply tire States and Europe, regulations of the or the protector ply of a radial tire, Federal Aviation Administration or this rubber loss causes aircraft (FAA) and the Joint Aviation Author- vibrations. ities, respectively, require retreading and/or repairing of aircraft tires in ¥ Asymmetrical (laterally uneven) certified retread-and-repair stations, tread wear — which may occur which employ certified technicians,

8 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 maintain service histories of indi- SAE’s recommended practice — like vidual tires, and can repair many major tire manufacturers’ care and types of damage if cords have not service publications — focuses on the been cut or damaged. primary areas where tire damage may occur: the tread, the sidewall, the bead Tests to determine a tire’s suitability area and the inner liner.6 for retreading require demounting the tire/wheel assembly and removing the The following factors are consid- tire. A separate category of tire-wear ered important by developers of limits and damage limits applies to SAE’s recommended practice, the assessment of demounted tires for the civil aviation authorities and sever- purpose of determining retreadability. al major tire manufacturers. Main- (Retreading limits established by the tenance technicians are responsible original tire manufacturers are be- for determining whether any guide- yond the scope of this article. Never- line is applicable to any specific theless, within these limits, tires aircraft or operating conditions, with evenly worn tread, with a flat- and how to comply with the air- spotted tread or with numerous cuts worthiness requirements of aviation in the tread area typically are accept- authorities. able for renewal of the tread alone or for renewal of a bias-ply tire’s tread In the tread area, cuts, cracks, and reinforcing ply or a radial tire’s foreign objects or other tread anom- tread and protector ply.) alies (called “injuries”) should be evaluated based on length and width of each injury on the outermost Limits for Tire Damage cord-body ply; the number of inju- Also Involve ries that meet or exceed these dimen- Common Principles sions; the extent (percentage) of penetration of any injury through the The Society of Automotive Engineers cord-body plies; and the relative po- (SAE) in 1995 published guidelines sition of injuries that exceed a speci- representing currently accepted in- fied cord-penetration limit along the dustry practices regarding damage circumference of the tire. to bias-ply aircraft tires, the most widely used type of tire construction. One of the most serious problems is SAE’s guidelines did not include tread separation, a splitting or void radial tires, but recent tire care and between tread and tread-reinforcing service literature from several major components caused by the failure of tire manufacturers shows that simi- tread adhesion. Tread separation typ- lar principles apply to radial tires. ically warrants removal of the tire

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 9 from service. Tests by tire manufac- cracking extends under a tread-rib turers have established that excessive cut. Limits to determine whether a tire heat generation in tire/wheel assem- must be removed from service may blies from underinflation or overload- be linked to the extent of exposure of ing are significant causes of tread reinforcing ply (on bias-ply tires) or separation. Some manufacturers re- protector ply (on radial tires), or may fer to one type of tread separation — be linked to exact measurements of tread delamination — to describe par- cracking, peeling or undercutting. tial or complete loss of the tread to the tread fabric ply or casing plies. The appearance of cord-ply fabric also may warrant removal of a tire Pieces of glass, stones, metal and oth- when tread chipping or tread chunk- er foreign objects embedded in the ing (missing pieces of tread) are tread or penetrating the cord body found, circumferential cracking oc- should be marked for removal. Re- curs at the base of a tread groove, or moval should be done using correct chevron cutting is observed (caused tools and techniques (including ap- by some cross-grooved runway sur- proved eye protection) after the tire faces). A crack in the tread where a has cooled to ambient temperature tread joint or splice separates in a and has been deflated. radial direction — open tread splice — also warrants tire removal. One manufacturer’s damage limits call for removal of a tire if cord-ply For the sidewall area, SAE’s recom- fabric can be seen without spreading mended practice and an FAA advisory the cut or if cuts extend more than circular7 generally consider normal half of the width of a rib and deeper weather checking or ozone checking than 50 percent of the remaining (random shallow surface cracks), radi- groove depth. Another manufactur- al and circumferential cracks, shallow er’s limits are linked to exposure or cuts, gouges and snags to be repairable penetration of the casing-cord body if these anomalies do not exceed spec- of a bias-ply tire or the tread-belt ifications for penetration of the rein- layers of a radial tire, specify a max- forcing plies (for example, deeper than imum diameter for superficial open- one ply). Nevertheless, as in the tread ings by foreign objects, and require area, several anomalies warrant imme- tire removal if a tire cut or injury sev- diate removal of a tire from service. ers a tread rib or extends across a These include separation of sidewall tread rib. Tread cuts may progress to rubber from the casing fabric and rup- a peeled rib (partial or total circum- ture of the tire casing at the sidewall. ferential delamination of a tread rib) One insidious type of sidewall damage or rib undercutting, in which groove (that is, an initially invisible damage

10 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 that may compromise safety over time) separation and damage from exces- is a lower-sidewall compression flex sive heat generation (such as melt- break. This break may begin with ed, blistering or brittle rubber, or cracks on the inner liner side, then solidified cord-ply fabric). weaken the tire through pressure loss. Underinflation of tires and overload- Inner-liner damage and splices should ing of tires are recognized causes of be assessed for length, number and sidewall damage. Pressure loss that position. Deterioration that warrants cannot be traced to another cause may removal of the tire from service may be a symptom of lower-sidewall include distorted and wrinkled rub- compression flex break. Demounting ber in a tubeless-tire inner liner; fab- of the tire and inspection using an ric fraying and broken cords in a approved checklist are appropriate to tube-type tire inner liner; and liner diagnose the problem before carcass blisters or liner separations that ex- plies severely deteriorate and cause a ceed removal limits regarding size, massive sidewall-ply separation. position and number. Small liner blisters (diameter not more than two In the bead area of the tire (the in- inches [five cm]), particularly in tube- side edge that seals against the wheel less tires, typically should be left as flange) repairability is determined found to avoid creating a slow leak. by ruling out damage to cord-body plies and verifying that the tire-to- Some tire wear and tire damage in- wheel fit will retain the specified volve causal factors that can be inflation pressure. The bead-area controlled, including improper main- surfaces should be smooth, and wear tenance and improper pilot technique. should be within limits. Tire-tool Moreover, the resulting tire failures chafing or chafing by the wheel can cause significant damage that flange should not adversely affect leads to an incident or accident. Line cord plies or cause ply separation. experience and tests by airframe and In the bead area, hoops of steel wire tire manufacturers have demonstrated called “wire beads” anchor the cas- that sound principles for managing ing plies and provide a strong mount- tire wear and tire damage effectively ing surface for contact with the increase the margin of safety in air- wheel flange. Among serious prob- line operations.♦ lems that typically warrant scrapping the tire — that is, permanent removal from service because even basic References retreadability limits would be exceeded — are protruding or exces- 1. The CHIRP Charitable Trust. sively kinked bead wire, bead-wire “Aircraft Tires (Wheels).” U.K.

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 11 Confidential Human Factors 4. Michelin Aircraft Tire Corp. Incident Reporting Program Aircraft Tire Care & Service. Search Request No. 99/3/02, Greenville, South Carolina, U.S.: March 25, 1999. The search, re- Michelin Aircraft Tire Corp., quested by Flight Safety Foun- 1997. dation, found two deidentified reports. 5. Aviation Products Division, The Goodyear Tire & Rubber 2. Examples in this article were se- Co. The Comprehensive Guide lected from three databases. to Aircraft Tire Care and The data included air carrier Maintenance. Akron, Ohio, U.S.: incidents and accidents from The Goodyear Tire & Rubber January 1983 to January 1999, Co., 1998. maintained by the U.S. Federal Aviation Administration (FAA) Aircraft Tire Sales Department, and the U.S. National Transpor- Bridgestone Corp. Tire Speci- tation Safety Board (NTSB), fication & Maintenance Manual. and the accident and incident Tokyo, Japan: Bridgestone Corp., report system (ADREP) main- 1997. tained by the International Civil Aviation Organization. Narra- 6. Society of Automotive Engineers. tive information did not provide “Aircraft New Tire Standard: Bias causal factors consistently. and Radial.” Aerospace Standard Nevertheless, studies by tire No. AS4833. June 1995. “Aircraft manufacturers have associated Tire Retreading Practice: Bias some of the types of tire/wheel- and Radial.” Aerospace Recom- assembly failures with abnormal mended Practice No. ARP4834. tire wear and tire damage. November 1995. Warrendale, FAA and NTSB reports were Pennsylvania, U.S. developed from official records by Air Data Research, 13438 7. FAA. “Chapter 9: Landing Bandera Road, Suite 106, Gear Systems.” Airframe and Helotes, Texas 78023 U.S. Powerplant Mechanics Airframe Handbook. Advisory Circular 3. The CHIRP Charitable Trust. 65-15A. 1976.

12 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 MAINTENANCE ALERTS

Autopilot-switch flight, because the peak airplane re- Malfunction Causes sponse lagged behind the peak flight- Airplane Upset crew inputs by up to one second,” said NTSB.

The U.S. National Transportation “This significant lag in airplane Safety Board (NTSB) said that an in- response led to an airplane-pilot flight upset of a McDonnell Douglas coupled response in which the flight DC-10-10 was caused by a mal- crew was continuously out of phase functioning control-wheel-steering with the airplane’s motions. Three (CWS) sensor that sent erroneous oscillations were completed before signals to the autopilot. NTSB rec- the flight crew was able to dampen ommended modification of the sen- the airplane’s response and return to sor and education of flight crews on level flight.” the potential for similar upsets. Of the 298 occupants, three occu- The DC-10, operated by Continental pants (flight attendants) were seri- Airlines, departed from Los Angeles, ously injured, and five occupants California, U.S., on May 21, 1998, sustained minor injuries. The air- and was climbing through Flight Lev- plane was not damaged. After the el 310 when an uncommanded pitch- upset, the crew dumped fuel, re- attitude increase occurred. turned to Los Angeles and landed the airplane without further incident. The captain immediately discon- nected the autopilot. “Flight data “Postflight examination of the air- recorder (FDR) data showed that the plane revealed that the CWS sensor airplane then went through four located in the first officer’s control up-and-down pitch oscillations, the column was malfunctioning and most severe of which attained verti- sending an erroneous signal to the cal accelerations of +1.84 [Gs] to autopilot computer,” said NTSB. Ð1.12 Gs,” said NTSB. The malfunction resulted from a The first oscillation occurred imme- short circuit caused by material con- diately after the uncommanded pitch tamination. Silver, chlorine and up. “Three more complete nose-up sulfur were found inside the CWS and nose-down cycles occurred … as sensor. NTSB said that the most the flight crew tried to regain level likely sources of the silver were

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 13 gold-plated silver wires connecting accident involving a US Airways strain gauges with the sensor. Fokker 100. The airplane was substan- tially damaged during an emergency The sensor manufacturer, Kulite landing at Birmingham (Alabama, Semiconducter Products, in 1975 U.S.) International Airport. began to use gold wires or gold- plated platinum wires, rather than “The flight crew had declared an emer- gold-plated silver wires. gency because of a dual hydraulic- system failure that occurred after the NTSB recommended that the U.S. airplane was struck by lightning,” said Federal Aviation Administration re- NTSB. quire DC-10 operators to replace gold-plated silver wires with gold A misinstalled connector in the al- wires or gold-plated platinum wires, ternate brake system caused the and to ensure that DC-10 flight crews brakes to lock when the crew applied are provided information regarding brake pressure on landing. “Three the potential for airplane upsets main-landing-gear tires failed, and caused by CWS-sensor malfunctions the airplane departed the runway, and the potential for overshoots in slid through the grass and came to recovering from upsets, caused by rest on an adjacent taxiway,” said the airplane’s lag in responding to NTSB. None of the 92 occupants control inputs. was injured.

The right side of the fuselage had Lightning Damage numerous small lightning-burn Spurs Call for Action marks, and the right horizontal On Bonding Straps stabilizer had a large lightning-burn mark. The horizontal-stabilizer-hinge The U.S. Federal Aviation Adminis- bonding strap, which provides a low- tration (FAA) should review the de- resistance path to allow electrical cur- sign of the horizontal-stabilizer-hinge rent to safely discharge, had been bonding straps on Fokker 70 and 100 melted by an electrical overload. airplanes, and require operators to modify their airplanes to increase “Once the bonding strap failed on lightning-strike protection, said the the accident airplane, the remainder U.S. National Transportation Safety of the electrical current arced across Board (NTSB). the hydraulic lines in the vertical tail, which led to their failure,” The recommendation was generated said NTSB. The no. 1 hydraulic- by the investigation of a Feb. 26, 1998, system pressure line and the no. 2

14 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 hydraulic-system return line had The pilot later selected the autopilot 0.25-inch-diameter (0.64-centimeter- off and then found that he could diameter) holes, and both hydraulic move the control yoke partially to the reservoirs were empty. left but not to the right. “The autopilot was checked and confirmed to be disengaged,” said the report. “The Control Problem Leads passenger [also a private pilot] To Off-airport Landing checked his controls and confirmed the restriction. On May 22, 1998, the pilot of a Piper Warrior made a precautionary “The pilot reported that even with landing near Ripple Village, Deal, considerable force, it was not possi- Kent, England, after aileron control ble to move the yoke to the right, al- became restricted. The pilot sustained though full control of rudder and minor injuries, his passenger was not elevators appeared to remain avail- hurt, and the airplane was substan- able. The decision was taken to make tially damaged. Investigators found a precautionary landing in the near- that the autopilot switch functioned est suitable field.” The left wing sep- intermittently. arated from the airplane during the landing. The U.K. Air Accidents Investigation Branch (AAIB), in its report on the Initial examination of the airplane accident, said that the private pilot revealed no flight-control-system conducted a full-and-free control anomalies. The autopilot then was check before departure. During the removed from the airplane and test- flight, the low-voltage indicator light ed at an autopilot-overhaul facility. illuminated. “Functional testing was carried out “The pilot reported that the ammeter with particular reference to the action indication remained normal and no of the unit’s controls during disen- other electrical services appeared to gagement,” said the report. “It was have been affected,” said the report. found that the on-off switch was not The pilot reduced electrical loads but always positive in its action, with a continued using the autopilot with the tendency to stick in both the ‘on’ and heading-hold mode engaged. ‘off’ positions.”♦

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 15 NEWS & TIPS

Process Restores For more information: Clearfix Corp., Acrylic Transparencies 150 E. 58th St. 34th Floor, New York NY 10155 U.S. Telephone: +1(212) The Clearfixª Acrylic Restoration 861Ð3161. Process enables maintenance technicians to repair scratch damage Training Program to stretched-acrylic cabin windows on aircraft. The process makes Probes Maintenance scratches disappear on the majority Human Factors of noncoated-acrylic transparency surfaces without causing optical dis- Error management is the subject of tortion, removing significant amounts Engineering Solutions to Human of acrylic or degrading the strength Problems, a new training program for or durability of windows, said the maintenance technicians, maintenance manufacturer. managers, safety managers, engineers, maintenance apprentices and main- Two solutions containing abrasives, tenance trainees. suspension agents and surfactants (surface-active agents) are applied The program helps to fulfill require- in sequence with hard and soft appli- ments for human-factors training of cator pads mounted on a variable- licensed engineers, said the Interna- speed power drill. The abrasive grit tional Federation of Airworthiness in the solutions gradually becomes (IFA), which provided technical smaller during the process. Transpar- support and financial support for encies are cleaned with the product’s production of the program. antistatic cleaner before, during and after applying the solutions. The requirements for human factors training of licensed engineers are Product testing has been performed in International Civil Aviation Orga- by the University of Dayton Research nization Annex 1 amendment no. Institute, and regional airlines and 161. The amendment requires all other aviation organizations have licensed engineers to have knowl- field-tested the process. Technical edge of “human performance and approvals also have been obtained limitations relevant to the duties of from major aircraft manufacturers, an aircraft maintenance holder,” said the company. said IFA.

16 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 The program comprises 11 elements, VIS-PROBE is supplied with a certificate including four videotapes, briefing of calibration and the manufacturer and training materials, case histories states that the product accommodates and human-factors study materials. all turbine-engine oils, including PRF- 23699 and DOD-L-85734 types. Use The program was produced by TVC of the device requires minimal training. Television Communications. The program costs US$3,500.00; IFA For more information: Airborne members receive a 10% discount. Analytical Labs, P.O. Box 518, East Hanover, NJ 07936. Telephone (800) For more information: TVC Televi- 989-7692 (U.S.); +1(973) 887-7410 sion Communications, 15 Greek ext. 235 (international). Street, London WIV 5LF. Telephone +44 171 734 6840. Device Measures Viscosity of Turbine-engine Lubricant

VIS-PROBE is an on-site test device designed to test oil viscosity and provide pass/fail results within 10 minutes. The device can be used to test lubricants for aircraft turbine Niagara Cutter engines, ground-based turbine en- Optimizerª gines and helicopter gearboxes, said the manufacturer. Machining Information On CD-ROM

Niagara Cutter’s Optimizerª inter- active CD-ROM provides product information, engineering charts and demonstration videos. Topics include metal-removal milling techniques and recommendations, sharpening and inspection data, a quick-reference Airborne Analytical Labs engineering-chart list, and a guide to Vis-Probe end-mill styles.

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 17 Also included are a video of the elements to remove moisture and company’s end-mill manufacturing contaminants, a honeycomb base processes and a short demonstration core, gaskets and seals. video showing the chip evacuation and performance of coated end mills. For more information: LA-MAN Corp., 700 Glades Court, Port For more information: Niagara Orange, FL 32127 U.S. Telephone: Cutter, 200 John James Audubon (800) 348-2463 (U.S.); +1(904) 304- Pkwy, Amherst, NY 14228 U.S. 0411 (international). Telephone +1(716) 689-8400. Filters Maintain Compressed-air System Efficiency

LA-MAN Corp. supplies filter- replacement kits for its Extractor/ Dryer¨ two-stage compressed-air- DuPont line filtration systems. Routine fil- SONTARA EC¨ ter replacement helps maintain compressed-air systems and air- Industrial Wiper Made operated tools and ensures that they Of Engineered Cloth can operate more efficiently, said the manufacturer. The kits include SONTARA EC¨ brand engineered- first-stage and second-stage filter cloth wipers made by DuPont are suitable for aircraft-maintenance uses including general-purpose cleaning and surface preparation in prepaint ap- plications, said the manufacturer.

SONTARA EC is a spun-lace wiper that resists abrasion and solvents, contains no binders or glues, is low- linting, and is highly absorbent in water, oil and solvents.

For more information: DuPont Sontara LA-MAN Technologies, 1002 Industrial Rd., Old Filter Replacement Kits Hickory, TN 37138 U.S. Telephone

18 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 (888) 476-6827 (U.S.); +1(615) 385- ranging from five in. (12.7 cm) long 1100 ext. 274 (international). to 47 in. (119 cm) long.

Cable Ties Are For more information: Nelco Prod- Strong and ucts, 22 Riverside Dr., Pembroke, Corrosion Resistant MA 02359 U.S. Telephone (800) 346-3526 (U.S.); +1(781) 826-3010 (international). Nelco Self-Lock Stainless Steel Cable Ties are designed for use where rough weather, salt spray, extreme Diagnostic Device vibration, radiation, chemical expo- Aids Detection of sure and other hostile environments Intermittent Defects require a strong, durable cable tie, In Avionics said the manufacturer. The IFD-2000 Intermittent Fault The permanent ties feature 150- Detector simultaneously and con- pound (68-kilogram) minimum loop tinuously monitors hundreds of tensile strength; are 3/16 inch (in.; 0.48 lines to detect and diagnose intermit- centimeter [cm]) wide by 0.01 in. (0.03 tent defects in electronic circuit cm) thick; and are available in sizes boards and related equipment, said the manufacturer. The device is a computer-operated tester-analyzer that employs a proprietary “front end” hardware neural network to perform real-time data reduction with sensor-fusion techniques. The basic unit monitors up to 256 single- ended lines, and can be expanded to 4,096 test points/input lines with additional modules.

Because the device tests all lines simultaneously and continuously, it can identify small or short-duration intermittent failures. The device’s sensitivity is programmable to detect ohmic events as low as 20 ohms and Nelco Self-Lock Stainless wide-open intermittents as short as Steel Cable Tie 130 nanoseconds in duration.

FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 19 For more information: Universal components in aircraft landing gear, Synaptics, 1801 W. 21st Street, said the manufacturer. Ogden, UT 84401 U.S. Telephone +1(801) 731-8508. Under field-maintenance conditions, the ring halves can be articulated Aviation Degree around the circumference to allow the On-line cut ends to meet. This articulation results in the unit assembly opening as The University of Nebraska at Oma- a conventional scarf-cut backup ring. ha Aviation Institute and College of Continuing Studies are offering an In- For more information: Greene, Tweed ternet-based aviation studies degree. & Co., Aerospace & Defense Group, Students can complete from 24 to 30 1555 Bustard Rd., Suite 130, P.O. Box hours of aviation studies course 217, Kulpsville, PA 19443-0217 U.S. work, and these courses can be com- Telephone: +1(215) 256-9521. bined with other academic and non- traditional credit to complete the Flexible Grinding requirements for a bachelor’s degree Discs Used for with a concentration in aviation Aluminum, Steel studies. Flexible grinding discs made of cot- For more information: Aviation ton fiber and impregnated with alu- Institute, Allwine Hall 422, Univer- minum oxide provide long service, sity of Nebraska at Omaha, Omaha, said the manufacturer. Rex-Cut¨ Cut- NE 68182-0508 U.S. Telephone N-Finishª Discs are nonloading on (800) 335-9866 (U.S.); +1(402) aluminum and are also suitable for 595-2342 (international). use with mild steel and stainless steel. The discs are available in 24-, 36-, Backup Ring 54-, and 80-grit sizes and come in 4.5- Protects Elastomeric inch (11.4-centimeter) and seven- Components inch (18-centimeter) diameters.

The Split-Lockª Backup Ring from For more information: Rex-Cut Prod- Greene, Tweed & Co. is designed ucts, 960 Airport Road, P.O. Box for field-maintenance technicians who 2109, Fall River, MA 02722 U.S. have experienced difficulty assem- Telephone: (800) 225-8182 (U.S.); bling multipiece split backup-ring +1(508) 678-1985 (international).♦

20 FLIGHT SAFETY FOUNDATION ¥ AVIATION MECHANICS BULLETIN ¥ MAYÐJUNE 1999 BLANK INSIDE BACK COVER deRIO Janeiro,Brazil] November 8–11, 1999 Enhancing Safety in the 21st Century

Hosted by Embraer

Lider

TA M

Transbrasil

Varig

VASP

International Federation International Air Transport of Airworthiness Flight Safety Foundation Association A Joint Meeting of 52nd FSF annual International Air Safety Seminar, 29th IFA International Conference and IATA For information contact Ann Hill, tel. +1(703) 739-6700, ext. 105 or Ahlam Wahdan, ext. 102

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