Embraer EMB145 Operation Manual page 291

AIRPLANE SUPPLEMENTARY
PROCEDURES
OPERATIONS
ENVIRONMENTAL
MANUAL
FREEZING RAIN AND FREEZING DRIZZLE
Atmospheric conditions involving freezing rain or freezing drizzle
associated to supercooled large droplets (SLD), may present a
condition that is beyond those for which the airplane was certified.
Both freezing rain and freezing drizzle can exist down to ground level
and cause ice to form quite rapidly on all surfaces even during short
exposures and on areas not normally known to be subjected to ice
accretion. This means that the airplane is not designed to fly under
freezing rain/drizzle (SLD) conditions.
If the crew notices abnormal ice formation on areas not usually
affected by this phenomenon, or ice formation on the previously
treated upper surface of the wings, they must consider to be flying
under severe icing conditions. In this case, the anti-ice system is
failing to reduce or control ice formation. The crew must then exit
freezing rain/drizzle conditions as soon as possible since continuous
flight under such conditions is, indeed, quite hazardous.
FLAP OPERATION UNDER ICING CONDITIONS
Ice accretion on an airplane depends mainly on the cloud type
encountered, the cloud liquid water content and droplet size, and
weather conditions. Icing should be expected when flying in visible
precipitation, such as rain or cloud droplets, with a temperature
between +2°C and -10°C (between 35.6°F and 14°F).
Regardless of the airplane type, the wing, horizontal stabilizer, and
engine inlets are typically critical airplane parts for ice accretion and
are protected with anti-icing or de-icing systems. The wing flaps are
not equipped with a anti-icing or de-icing system and, therefore, if they
remain extended for a long period of time in icing conditions, ice may
build up on the flaps leading edge. This ice may cause difficulties in
retracting the flaps.
For a certain flight time in different weather conditions, the ice
accretion intensity may vary, being either trace, light, moderate, or
severe. Because of the varying conditions, it is not possible to state a
reliable time figure that would cover all situations.
Therefore, as a general policy, the use of flaps in icing conditions
should be avoided or minimized whenever possible.
Page Code
1-02-79 20 01
TEMPORARY REVISION 41.1
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