getting to grips with COLD WEATHER OPERATIONS 寒冷天气运行(35)

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When a large holdover time is expected or needed, a two-step procedure is recommended, using undiluted fluid for the second step.
B3.5.1 De-icing
Ice, snow, slush or frost may be removed from aircraft surfaces by heated fluids or
mechanical methods.
For maximum effect, fluids shall be applied close to the aircraft surfaces to minimize heat
loss.
Different methods to efficiently remove frost, snow, and ice are described in detail in the
ISO method specification. Refer also to the Aircraft Maintenance Manual (AMM).

● General de-icing fluid application strategy
The following guidelines describe effective ways to remove snow and ice.

Wings/horizontal stabilizers: Spray from the tip towards the root, from the highest point
of the surface camber to the lowest.

Vertical surfaces: Start at the top and work downward.

Fuselage: Spray along the top centerline and then outboard; avoid spraying directly onto
windows.

Landing gear and wheel bays: Keep application of de-icing fluid in this area to a
minimum.
It may be possible to mechanically remove accumulations such as blown snow. However,
where deposits have bonded to surfaces they can be removed using hot air or by
carefully spraying with hot de-icing fluids. It is not recommended to use a high-pressure
spray.

Engines: Deposits of snow should be mechanically removed (for example using a broom
or brush) from engine intakes prior to departure. Any frozen deposits, that may have
bonded to either the lower surface of the intake or the fan blades, may be removed by hot
air or other means recommended by the engine manufacturer.

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B3.5.2 Anti-icing
Applying anti-icing protection means that ice, snow or frost will, for a period of time, be prevented from adhering to, or accumulating on, aircraft surfaces. This is done by the application of anti-icing fluids.
Anti-icing fluid should be applied to the aircraft surfaces when freezing rain, snow or other freezing precipitation is falling and adhering at the time of aircraft dispatch.
For effective anti-icing protection, an even film of undiluted fluid is required over the aircraft surfaces which are clean or which have been de-iced. For maximum anti-icing protection undiluted, unheated Type II or IV fluid should be used. The high fluid pressures and flow rates normally associated with de-icing are not required for this operation and, where possible, pump speeds should be reduced accordingly. The nozzle of the spray gun should be adjusted to give a medium spray. The anti-icing fluid application process should be as continuous and as short as possible. Anti-icing should be carried out as near to the departure time as is operationally possible, in order to maintain holdover time. In order to control the uniformity, all horizontal aircraft surfaces must be visually checked during application of the fluid. The required amount will be a visual indication of fluid just beginning to drip off the leading and trailing edges. Most effective results are obtained by commencing on the highest part of the wing section and covering from there towards the leading and trailing edges. On vertical surfaces, start at the top and work down. The following surfaces should be protected by anti-icing:
　
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