JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
and the relative humidity is high, the possibility of induction icing exists. Ingestion of ice shed
ahead of the compressor inlet may cause severe foreign object damage (FOD) to the engine.
Compressor icing – Ice forming on compressor inlet screens and compressor inlet guide vanes
will restrict the flow of inlet air, eventually causing engine flameout. The reduction in airflow is
noticeable through a loss of thrust and a rapid rise in exhaust gas temperature. As the airflow
decreases, the fuel-air ratio increases, which in turn raises the temperature of the gases going to
the turbine. The fuel control attempts to correct any loss in engine RPM by adding more fuel,
which merely aggravates the condition. Ice build-up on inlet screens sufficient to cause turbine
failure can occur in less than 1 minute under severe conditions.
Ground icing hazards – We have already stressed the importance of removing all icing and frost
from an aircraft prior to takeoff. De-icing itself, however, can also be a hazard. De-icing fluids
(discussed in the next section) are highly corrosive to internal aircraft and engine parts. Thus, it
is imperative that de-icing crews understand the particular requirements for your type of aircraft.
Additionally, taxiing through mud, water or slush on ramps and runways can create a covering of
ice that can hamper the movement of flaps, control surfaces, and the landing gear mechanism.
Ice and snow on runways are conditions that affect braking action of aircraft. Braking action
varies widely with aircraft type and weight. Therefore, pilots must be aware of the limits to their
aircraft’s braking capabilities.
MINIMIZING OR AVOIDING ICING HAZARDS
Flight Path Options
Figure 4-10 — Options to Escape Icing
In coping with an icing hazard in flight, a pilot usually has two alternatives. First, the pilot can
climb to the colder temperatures where the precipitation will be frozen and therefore not an icing
hazard. Second, the pilot can descend to an altitude where the air temperatures are well above
freezing (Figure 4-10). However, if encountering clear icing in the freezing precipitation below
the clouds of a warm front, the aircraft is most likely in the cold air ahead of the warm front. In
this case, the best alternative may be to climb to warmer temperatures, across the frontal
boundary, as the freezing precipitation may extend all the way to ground level.
4-14 Version 3.2/Dec 08