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 airplane deicing service providers, need to be aware of the recent developments and recommendations for operating airplanes 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 aircraft 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 takeoff 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: Elevator 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 lubricants 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. runway 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 water 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 person nel 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 thrust reversers. runway deicing fluids are in the area of airplane deicing and anti-icing: such as wing rear spar, wing leading hydroscopic fluids, so they don’t dry out edge devices, horizontal stabilizer rear very quickly, causing them to leave a thin spar, vertical stabilizer, 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 brake 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., Type ii, 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 wheel 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 brakes 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 potassium and sodium 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