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Airlines need to be aware of recent developments in winter operations and regularly update their cold weather operations procedures. Safe Winter operations

Airline engineering, maintenance, and flight personnel, as well as contracted deicing service providers, need to be aware of the recent developments and recommendations for operating in winter weather conditions.

By Haruhiko (Harley) Oda, Flight operations engineer; Philip Adrian, 737 chief Technical Pilot; Michael Arriaga, Service engineer; Lynn Davies, Aerodynamics engineer; Joel Hille, Service engineer; Terry Sheehan, 737 Technical Pilot; and E.T. (Tom) Suter, Service engineer

Safe winter operations require special THE cLEAn-AirPLAnE cOncEPT frost, ice, or snow may reasonably be procedures by airline maintenance, expected to adhere to the airplane, unless engineering, flight, and deicing personnel. The “clean-airplane” concept is derived the certificate holder has an approved These procedures include deicing, anti- from U.S. Federal Aviation Administration ground deicing/anti-icing program in its icing, cold weather maintenance, and (FAA) Federal Aviation regulation (FAr) operations specifications that includes flight operations. 121.629, which states, “no person may holdover time (HoT) tables. This article discusses recent develop- take off an when frost, ice or snow The european Aviation Safety Agency ments for winter operations. intended is adhering to the wings, control surfaces, (eASA), Transport canada civil Aviation for both maintenance and flight crews, propellers, engine inlets, or other critical (TccA), and other regulatory authorities it provides operators with guidance for surfaces of the aircraft or when the have requirements similar to FAr 121.629. reviewing and updating cold weather would not be in compliance with paragraph The clean-airplane concept describes an operations procedures. This article also (c) of this section. Takeoffs with frost under airplane that is aerodynamically clean — outlines general concepts and tips on safe the wing in the area of the fuel tanks may that is, free of frozen contaminants. The winter operations. be authorized by the Administrator.” clean-airplane concept is important The FAr also prohibits dispatch or because airplane takeoff performance is takeoff any time conditions are such that based upon clean surfaces until liftoff.

05 WWW.boeing.com/commerciAl/AeromAgAzine figure 1: control maintenance and ground crews should establish an inspection and cleaning schedule for deicing/ anti-icing fluid residue to help ensure that no flight control restrictions will occur.

An airplane is designed using the predict- When thickened airplane deicing/anti-icing (when applicable), and the bilge area able effects of airflow over clean wings. fluids (i.e.,SAe international Types ii, iii, of the tail cone. Visually inspect for dry contaminants such as frost, ice, or snow and iV fluids) dry, they may leave a very fine, or rehydrated residues in these areas. adhering to the wings disturb this airflow, powdery residue in critical areas in wings This inspection and cleaning should resulting in reduced lift, increased drag, and stabilizers. This residue can rehydrate be performed in accordance with the increased stall speed, potentially severe roll and expand into gel-like materials that can recommendations found in the Amm for problems due to uneven lift, and possible freeze during flight and cause restrictions in the specific airplane model involved. abnormal pitch characteristics. the flight control systems (see fig. 1). (For ■ Apply and corrosion inhibitors more information, see AERO first-quarter as necessary to the areas where residue 2007.) As a result, operators should: cleaning occurs. cOnSiDErATiOnS fOr MAinTEnAncE AnD grOunD crEwS ■■ be aware of how frequently airplanes Airplane deicing/anti-icing fluids and many are being deiced/anti-iced. deicing fluids are not compatible — Airplane operation in cold weather ■■ be aware of whether a one- or two-step interaction between the two may contribute conditions can cause special problems application process is being employed. to the formation of gel residues. When because of the effects of frost, ice, snow, While recognizing that it is not possible these fluids combine, the salts in some slush, and low temperature. The airplane at some locations, boeing recommends runway fluids enhance the separation of the maintenance manual (Amm) provides using a two-step process, preferably polymers contained in thickened airplane procedures for removal of contaminants with Type i fluid and/or hot as the fluids, leading to a more rapid formation of from the airplane and the prevention of first step. The application of hot water gel residues. subsequent accumulation of frost, ice, or heated Type i fluid as the first step of snow, or slush. in addition, the operator a two-step process has been shown to When runway deicing fluid contaminates must ensure that the maintenance proce- minimize the formation of residue gels. thickened airplane anti-icing fluid, there can dures for winter operations are appropriate ■■ ensure that proper procedures, including be significant degradation of the fluid’s for the weather conditions. (See “The storage, handling, and application performance. HoT values can be reduced basics of deicing and anti-icing” on page 9 of fluids, are being followed by airline and adherence or unacceptable flow-off and “general precautions during winter personnel or contracted deicing may result. runway deicing fluid can get operations” on page 11.) service providers. onto the wings and tails by various means, boeing recommends that maintenance ■■ establish an inspection and cleaning such as spray from the nose gear, spray and ground crew personnel and contracted schedule for thickened fluid residue kicked up by the engine exhaust of other airplane deicing service providers acquaint to help ensure that no flight control airplanes, or from activation of the engine themselves with these recent developments restrictions will occur. examine areas reversers. runway deicing fluids are in the area of airplane deicing and anti-icing: such as wing rear , wing leading hydroscopic fluids, so they don’t dry out edge devices, horizontal rear very quickly, causing them to leave a thin spar, , auxiliary power wet layer on the wing that can be difficult unit bay, control tabs and linkages to see. This implies that the use of hot

06 Aero qUArT erly qTr_04 | 10 figure 2: Damage to carbon disks caused by runway deicers The damaged stator disk drive lugs on this carbon heat-sink demonstrate the type of damage alkali metal-based runway deicers can cause to carbon brake disks.

Stator Disk Drive lugs

Stator Disk Drive lugs missing (oxidized)

water or Type i fluid to clean the wing prior comply with FAA Special Airworthiness on runways contaminated by slush, to the application of thickened anti-icing information bulletin nm-08-27 and eASA snow, standing water, or ice, the use of fluid (i.e., Typeii , iii, or iV) is even more Safety information notice 2008-19r1, the fixed derate reduced thrust is permitted, important than previously thought. on main gear removal/installation provided that airplane-takeoff-performance September 14, 2010, eASA issued Safety sections of applicable Amms have been planning accounts for the runway surface information bulletin 2010-26 on this revised to recommend inspection of the condition. Use of the assumed temperature subject, recommending the use of the carbon brake assembly for signs of reduced thrust method, alone or in two-step application process. catalytic oxidation damage whenever a combination with a fixed derate, is not wheel and tire assembly is removed. permitted on contaminated runways. catalytic oxidation of carbon may boeing has released several service boeing does not recommend takeoffs result from exposure of the brakes to alkali letters regarding the corrosion caused by when slush, wet snow, or standing water metal (i.e., organic salt)-based runway alkali metal-based runway deicers on depth is more than 0.5 inch (13 millimeters) deicers. This may cause severe damage various airplane parts, including hydraulic or dry snow depth is more than 4 inches to the brakes and drastically shorten their tubes and cadmium-plated electrical (102 millimeters). (See “general precautions service life. These runway deicers have also connectors. during winter operations” on page 11.) caused corrosion of electrical connectors boeing recommends that flight crews and hydraulic system components. make themselves aware of the following in the 1990s, runway deicing materials cOnSiDErATiOnS fOr fLigHT crEwS recent developments in the area of winter containing and acetate operations: were introduced (potassium and sodium Winter or cold weather operations are formate were introduced later) as an generally associated with a combination of Starting with the 2010 winter season, HoT alternative to urea and glycol runway low temperatures and frost, ice, slush, or guidelines for Type i fluids include a new set deicers. Urea and glycol runway deicers snow on the airplane, ramps, taxiways, and of times to be used when the fluids have contribute to an increase in the biological runways. The airplane flight manual AFm( ) been applied to composite surfaces. and chemical oxygen demand of water defines icing conditions as when the Testing performed during the last three systems surrounding airports and are more outside air temperature (oAT) on the ground winter seasons has shown that HoT values toxic to aquatic life than the alkali metal- or total air temperature (TAT) in flight is for Type i fluids on composite surfaces based runway deicers. 50 degrees F (10 degrees c) or less and are significantly shorter (on the order of Following the introduction of the new any of the following exist: 30 percent) than for aluminum surfaces. runway deicers, some operators reported Although this topic has been discussed in ■ Visible moisture (e.g., clouds, fog that their airplanes equipped with carbon the FAA notice of its “FAA-Aproved Deicing with visibility of one statute mile brakes began experiencing catalytic Program Updates” for the last two winter [1,600 meters] or less, rain, snow, oxidation of the carbon brake heat-sink seasons, this year both the FAA and TccA sleet, or ice crystals). disks (see fig. 2). in order to help operators are publishing separate HoT guidelines ■ ice, snow, slush, or standing water on of airplanes equipped with carbon brakes for composite surfaces. in addition to the ramps, taxiways, or runways.

07 WWW.boeing.com/commerciAl/AeromAgAzine The use of hot water or Type i fluid to clean the wing prior to the application of thickened anti-icing fluid (i.e., Type ii, iii, or iV) is even more important than previously thought.

extensive use of composites on newer in-flight operational data is published as The 787 and 747-8 qrH advisory data models, many older models also have advisory normal-configuration will be based on the TAlPA Arc recom- numerous composite surfaces (e.g., distance data in the performance in-flight mendations. changes to the qrH advisory spoilers, , flaps, slats, etc.). section of a quick reference handbook data for other models, such as the 777 and (qrH). The data is provided as unfactored the next-generation 737, will await final During taxi-out, avoid using reverse thrust data for operators who use FAA require- rulemaking. However, boeing can provide on snow- or slush-covered runways, ments. The advisory data in the qrH for guidance on how existing qrH normal- taxiways, or ramps unless absolutely operators who use Joint Aviation Authorities configuration landing data can be adjusted necessary. Using reverse thrust on snow- or eASA requirements includes a 1.15 factor to meet the intention of the TAlPA Arc or slush-covered ground can cause slush, for non-dry runway conditions. The advisory recommendations. water, and runway deicers to become data provided by boeing is based on the airborne and adhere to wing surfaces. use of reverse thrust and a 1,000-foot SuMMAry (305-meter) flare distance. AirPLAnE PErfOrMAncE The FAA has chartered an aviation Airlines need to be aware of recent rulemaking committee (Arc) on takeoff developments in winter operations and boeing currently provides two different and landing performance assessment review and update their cold weather landing-distance data sets to operators: (TAlPA) to ensure that industry practices operations procedures accordingly. dispatch data and in-flight operational data. have adequate guidance and regulation For more information, please contact for operation on non-dry, non-wet runways Dispatch landing data is used during flight Harley oda at [email protected]. (i.e., contaminated runways). based planning to determine the maximum land- on the recommendations made by the ing weight at which the airplane can land Arc, the advisory normal-configuration within the available landing distance at the landing-distance data for the 747-8 and destination or alternate airport. This data, 787 will include the following: referred to as certified data in theAFm , is based on standard-day temperature and ■■ braking action and runway surface accounts for airport pressure altitude and condition descriptions. runway wind. However, it does not account ■■ 7-second air (flare) distance. for the effect of thrust reversers or runway ■■ A 1.15 factor for operators that use slopes. non-dry runway conditions are FAA requirements. accounted for by factoring the dry runway dispatch landing-distance data.

08 Aero qUArT erly qTr_04 | 10 The basics of deicing and anti-icing

Deicing removes accumulated frost, ice, or are acceptable for use on all boeing fluids that can be used on airplanes. All snow from an airplane, typically through the airplanes (see fig. A): fluids must be requalified every two years. application of hot water or a hot mixture of military (mil) specifications for deicing/ ■■ Type i fluids are unthickened and typi- water and deicing fluid. Although there are anti-icing fluids (such asmil -A-8243D cally have a minimum of 80 percent other approved methods for deicing—such Type 1 and 2) are no longer kept up to glycol and a relatively low , as infrared heat or hot air—the primary date. boeing recommends updating service except at very cold temperatures. These method worldwide is the use of fluids. documents to reference SAe standards if fluids provide some anti-icing protection, they currently reference mil specifications. Anti-icing prevents the adherence of frost, primarily due to the heat required for ice, or snow to airplane surfaces for a deicing, but have a relatively short HoT. certain period of time (i.e., the HoT values). Standards for Type i fluids are published HOLDOvEr TiME While the same fluids used for deicing are in SAe Aerospace material Specification also used for anti-icing, SAe Types ii, iii, (AmS) 1424. HoT is the length of time that anti-icing fluid and iV fluids are more typically used for ■■ Type ii, iii, and iV fluids typically contain will prevent ice and snow from adhering anti-icing because they are thickened a minimum of 50 percent glycol in addi- to and frost from forming on the treated to stay on the airplane and thus provide tion to polymer thickening agents. The surfaces of an airplane. These times are longer HoT protection. They are most thickening agents delay the flow-off of only guidelines; a number of variables can effective when applied unheated and the fluids from the airplane surfaces. As a reduce protection time, including: undiluted to a clean airplane surface. result, Type ii, iii, and iV fluids provide ■ The heavier the precipitation, the shorter Whether used for deicing or anti-icing, longer HoT values than Type i fluids. The the HoT. the fluids must be transported, stored, and flow-off characteristics of Type iii fluids ■ High winds or jet blast that cause the handled properly to be effective. operators make them more suitable for commuter fluid to flow off, decreasing the protec- must ensure that the fluid manufacturer’s airplanes with relatively low takeoff tion afforded by the fluid layer. guidelines are followed for the entire rotation speeds. Type iV fluids provide ■ Wet snow, which causes fluids to dilute deicing/anti-icing process. longer HoTs than Type ii fluids. Stan- and fail more quickly than dry snow. dards for Type ii, iii, and iV fluids are ■ An airplane skin temperature lower published in SAe AmS 1428. DEicing AnD AnTi-icing fLuiDS than outside air temperature. in accordance with AmS 1424 and 1428, ■ Direct sunlight followed by precipitation. The SAe standards define four types of all fluids must pass an Aerodynamic ■ The use of incorrect equipment to deicing and anti-icing fluids. These fluids Acceptance Test to be considered qualified apply fluids. figure A: identifying deicing and anti-icing fluids by color The four types of deicing/anti-icing fluids can be readily identified by their color.

Type i Type ii Type iii Type iV

APPLying DEicing/AnTi-icing For each winter season, the FAA fLuiDS mixture of Type i fluid and water, or a heated publishes an annual Approved Deicing mixture of water and thickened (Type ii, iii, or Program Update in an 8900.xx notice iV) fluid, followed by a separate application There are two methods for applying deicing (where the “xx” changes each year) that of thickened fluid for anti-icing protection. and anti-icing fluids. includes HoT guidelines for all commercially experience and testing have shown that available deicing/anti-icing fluids that are one-step process: This process accom- deicing with heated Type i fluid or a heated currently qualified. plishes both the deicing and anti-icing steps mixture of water and Type i fluid will help Similarly, TccA annually publishes tables with a single fluid application. Typically a remove residue from previous anti-icing fluid of HoT values in its Transport canada heated mixture of thickened fluid and water treatments. Deicing with heated thickened Holdover Time guidelines. is applied. fluid may contribute to residue formation.

Two-step process: This process involves deicing with heated Type i fluid, a heated general precautions during winter operations

for maintenance crews

These are general guidelines; refer to the engine inlets, exhausts, static ports, ■■ Proper maintenance procedures for land- Amm for definitive information. pitot-static probes, pitot probes, or ing gear during cold weather opera tion TAT probes. as defined in theAmm can help reduce ■ ice that has accumulated on the fan ■■ Do not spray hot deicing/anti-icing fluid degradation of the structural joints and blades while the airplane has been on or hot water directly on windows as it ensure optimal shock performance. the ground for a prolonged stop is called may cause damage. ■■ operating during cold weather can “ground-accumulated ice” and must be ■■ ensure that ice or snow is not forced into adversely affect the ability to properly removed before engine start. areas around flight controls during deicing. lubricate the joints. Where ■ ice that has accumulated on the fan ■■ remove all ice and snow from possible, perform scheduled blades while the engine is at idle speed passenger doors and girt bar areas at maintenance bases where the is called “operational ice” and is allowed before closing. temperature is above freezing. A heated to remain on the fan blades before taxi ■■ cargo doors should be opened only hangar is the next most effective means because the ice will be removed by when necessary. remove the ice and of ensuring proper lubrication. if lubrica- engine run-ups prior to takeoff. snow from the cargo containers before tion must be accomplished outside a ■ The right and left sides of the wing and putting them on the airplane. heated hangar in temperature below horizontal stabilizer (including the elevator) ■■ if SAe Type ii, iii, or iV fluids are used, freezing, the landing gear structure itself must receive the same fluid treatment, remove all of the deicing/anti-icing fluid should be heated by blowing hot air and both sides of the vertical stabilizer from the cockpit windows prior to directly onto the structure or into an must receive the same fluid treatment. departure to ensure visibility. enclosure around the structure. ■ Treat the wings and tails from leading ■■ Deicing/anti-icing fluid storage tanks ■■ The temperature surrounding the airplane edge to and outboard must be constructed of a compatible has a direct effect on both the volume of to inboard. material. For thickened fluids, the tanks the gas and the viscosity of the in the ■ Treat the from the nose and must be of a material that is not suscep- shock strut. boeing multi-model service work aft. Spray at the top centerline and tible to corrosion (e.g., stainless steel or letters provide procedures to ensure work outboard. fiberglass). This is particularly important optimum strut performance if an airplane ■ Do not point a solid flow of fluid directly for thickened fluids because their operates between two different regions at the surfaces, gaps in struc- viscosity can be permanently decreased with significantly different temperatures. ture, or antennas. instead, apply the if they are contaminated or exposed to ■■ Do not point a spray of deicing/anti-icing fluid at a low angle to prevent damage, excessive heat or mechanical shear fluid directly onto or brake while pointing aft for proper drainage. during handling and application. assemblies. ■ make sure that all of the ice is removed ■■ When there is ice, slush, snow, or ■■ remove contamination (e.g., frost, ice, during deicing. There may be clear ice standing water on the runways or slush, or snow) from the area where the below a layer of snow or slush that is taxiways during taxi-in, examine the main and nose gear tires will be positioned not easy to see. As a consequence, it airplane when it gets to the ramp. look when the airplane is parked at the gate. if may be necessary to feel the surface to for any damage to the airplane surfaces tires are frozen to the ramp, the airplane adequately inspect for ice. and for contamination that may have should not be moved until they are free. ■ Do not spray deicing/anti-icing fluids collected on the airplane. carefully directly into (APU) or remove the contamination.

11 WWW.boeing.com/commerciAl/AeromAgAzine for flight crews

These are general guidelines; refer to the ■■ operate the APU only when necessary During TAxi boeing flight crew operations manuals during deicing/anti-icing treatment. (Fcom) for definitive information. ■■ Do not operate the wing anti-ice system This guidance is applicable for normal on the ground when thickened fluids operations using all engines during taxi. (e.g., SAe Type ii, iii, or iV) have been PriOr TO TAxi ■ Allowing greater than normal distances applied. Do not use the wing anti-ice between airplanes while taxiing will aid system as an alternative method of ■ carefully inspect areas where surface in stopping and turning in slippery ground deicing/anti-icing. snow, ice, or frost could change or affect condi tions. This will also reduce the ■■ if the taxi route is through ice, snow, normal system operations. Perform a potential for snow and slush being slush, or standing water, or if precipita- normal exterior inspection with increased blown and adhering onto the airplane tion is falling with temperatures below emphasis on checking surfaces, pitot or engine inlets. freezing, taxi out with the flaps up. probes and static ports, air-conditioning ■ Taxi at a reduced speed. Taxiing on Taxiing with the flaps extended subjects inlets and exits, engine inlets, fuel-tank slippery taxiways or runways at exces- flaps and devices to contamination. vents, landing-gear doors, landing-gear sive speed or with strong crosswinds ■■ check the flight controls and flaps to truck beam, brake assemblies, and APU may cause the airplane to skid. Use ensure freedom of movement. air inlets. Takeoff with a light coating of smaller nose-wheel steering and ■■ if there are any questions as to whether frost (up to 1⁄8 inch [3 millimeters] thick) inputs. limit thrust to the the airplane has frozen contamination, on lower wing surfaces caused by cold minimum required. request deicing or proceed to a deicing fuel is allowable. However, all leading- ■ Use of differential engine thrust assists in facility. never assume that snow will blow edge devices, all control surfaces, the maintaining airplane momentum through off; there could be a layer of ice under it. horizontal tail, vertical tail, and upper a turn. When nearing turn completion, in rainy conditions with oAT near freez- surface of the wing must be free of placing both engines at idle thrust ing, do not assume that raindrops on snow, ice, and frost. reduces the potential for nose-wheel surfaces have remained liquid and will ■ Perform the normal engine start proce- skidding. Differential braking may be flow off; they could have frozen onto the dures, but note that oil pressure may more effective than nose-wheel steering surface. A similar issue can occur due to be slow to rise. Displays may require on slippery or contaminated surfaces. cold-soaked fuel in the wing tanks. additional warm-up time before engine ■ nose-wheel steering should be exer- ■■ ice that has accumulated on the fan indications accurately show changing cised in both directions during taxi. This blades while the airplane has been on values. Displays may appear less bright circulates warm through the ground for a prolonged stop is called than normal. the steering cylinders and minimizes the “ground-accumulated ice” and must be ■ engine anti-ice must be selected on steering lag caused by low temperatures. removed before engine start. immediately after both engines are ■ During prolonged ground operations, ■■ ice that has accumulated on the fan started, and it must remain on during all periodic engine run-ups should be blades while the engine is at idle speed ground operations when icing conditions performed per the boeing Fcom to shed is called “operational ice” and is allowed exist or are anticipated. Do not rely on the accreted ice. to remain on the fan blades before taxi airframe visual icing cues before activat- because the ice will be removed by ing engine anti-ice. Use the temperature engine run-ups prior to takeoff. and visible moisture criteria. 12 Aero qUArT erly qTr_04 | 10 BEfOrE/During TAkEOff operator coordination with local and control. Do not hold the nose gear off en-route air traffic control facilities is the runway when operating on slippery ■■ Do the normal before Takeoff Proce- recommended. or icy runways. dure. extend the flaps to the takeoff ■■ Use of is recommended. setting at this time if they have not been They will allow the pilot to better concen- DEScEnT extended because of slush, standing trate on directional control of the airplane. water, icing conditions, or because of if manual braking is used, apply moderate ■ Unless the airplane has fully automatic deicing/anti-icing. to firm steady pedal pressure symmet- activation of ice protection systems, ■■ Verify that airplane surfaces are free of rically until a safe stop is assured. anticipate the need for activating the ice, snow, and frost before moving into ■■ let the anti-skid system do its work. engine and/or wing anti-ice systems at position for takeoff. Do not the brake pedals. all times, especially during a descent ■■ in icing conditions, refer to the boeing ■■ Do not use asymmetric reverse thrust through instrument meteorological Fcom for guidance regarding static on an icy or slippery runway unless conditions or through precipitation. engine run-up before takeoff. necessary to arrest a skid. ■ When anti-ice systems are used ■■ before brake release, check for stable ■■ When using reverse thrust, be prepared during descent, be sure to observe engine operation. After setting takeoff for a possible downwind drift on a boeing Fcom minimum ePr/n1 limits (ePr), or n1, check slippery runway with a crosswind. (if applicable). that engine indications are normal, in ■■ During winter operations, it is even more agreement, and in the expected range. important than usual that the flight crew check that other flight deck indications LAnDing not attempt to turn off the runway until are also normal. the airplane has slowed to taxi speed.

■■ rotate smoothly and normally at Vr. ■■ The flight crew must be aware of the ■■ Taxi at a reduced speed. Taxiing on slip- Do not rotate aggressively when condition of the runway with respect to pery taxiways or runways at excessive operating with deicing/anti-icing fluid. ice, snow, slush, or other contamination. speed or with strong crosswinds may ■■ retract flaps at the normal flap ■■ Follow the normal procedures for cause the airplane to skid. retraction altitude and on the normal approach and landing. Use the normal ■■ The cold Weather operations Supple- speed schedule. reference speeds unless otherwise men tary Procedure in the boeing Fcom ■■ A larger temperature difference from directed by the boeing Fcom. specifies how far the flaps may be international Standard Atmosphere (iSA) ■■ Arm the and autospoiler retracted after landing in conditions results in larger errors. When systems, if available, before landing. where ice, snow, or slush may have con- the temperature is colder than iSA, true ■■ The airplane should be firmly flown onto taminated the flap areas. if the flap areas altitude is lower than indicated altitude. the runway at the aiming point. are found to be contaminated, flaps consider applying the boeing Fcom ■■ immediately after main-gear contact should not be retracted until maintenance cold Temperature Altitude corrections, with the runway, deploy the speed has removed the contaminants. especially where high terrain and/or brakes if not already deployed by the ■■ Use the engine anti-ice system during all obstacles exist near airports in combi- automatic system. ground operations when icing conditions nation with very cold temperatures ■■ Without delay, lower the nose-wheel to exist or are anticipated. (-22 degrees F/-30 degrees c or colder). the runway to gain nose-wheel directional

13 WWW.boeing.com/commerciAl/AeromAgAzine