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extreme cases, 2 to 3 inches of ice can form on the
leading edge of the airfoil in less than 5 minutes. It
takes but 1/2 inch of ice to reduce the lifting power of
some aircraft by 50 percent and increases the
frictional drag by an equal percentage.
b. A pilot can expect icing when flying in visible
precipitation, such as rain or cloud droplets, and the
temperature is between +02 and −10 degrees Celsius.
When icing is detected, a pilot should do one of two
things, particularly if the aircraft is not equipped with
deicing equipment; get out of the area of
precipitation; or go to an altitude where the
temperature is above freezing. This “warmer”
altitude may not always be a lower altitude. Proper
preflight action includes obtaining information on the
freezing level and the above freezing levels in
precipitation areas. Report icing to ATC, and if
operating IFR, request new routing or altitude if icing
will be a hazard. Be sure to give the type of aircraft to
ATC when reporting icing. The following describes
how to report icing conditions.
1. Trace. Ice becomes perceptible. Rate of
accumulation slightly greater than sublimation.
Deicing/anti-icing equipment is not utilized unless
encountered for an extended period of time (over
1 hour).
AIM 2/17/05
7−1−42 Meteorology
2. Light. The rate of accumulation may create
a problem if flight is prolonged in this environment
(over 1 hour). Occasional use of deicing/anti-icing
equipment removes/prevents accumulation. It does
not present a problem if the deicing/anti-icing
equipment is used.
3. Moderate. The rate of accumulation is such
that even short encounters become potentially
hazardous and use of deicing/anti-icing equipment or
flight diversion is necessary.
4. Severe. The rate of accumulation is such that
deicing/anti-icing equipment fails to reduce or
control the hazard. Immediate flight diversion is
necessary.
EXAMPLE−
Pilot report: give aircraft identification, location,
time (UTC), intensity of type, altitude/FL, aircraft type,
indicated air speed (IAS), and outside air temperature
(OAT).
NOTE−
1. Rime ice. Rough, milky, opaque ice formed by the
instantaneous freezing of small supercooled water
droplets.
2. Clear ice. A glossy, clear, or translucent ice formed by
the relatively slow freezing of large supercooled water
droplets.
3. The OAT should be requested by the AFSS/FSS or ATC
if not included in the PIREP.
7−1−23. Definitions of Inflight Icing Terms
See TBL 7−1−7, Icing Types, and TBL 7−1−8, Icing
Conditions.
TBL 7−1−7
Icing Types
Clear Ice See Glaze Ice.
Glaze Ice Ice, sometimes clear and smooth, but usually containing some air pockets, which results in a
lumpy translucent appearance. Glaze ice results from supercooled drops/droplets striking a
surface but not freezing rapidly on contact. Glaze ice is denser, harder, and sometimes more
transparent than rime ice. Factors, which favor glaze formation, are those that favor slow
dissipation of the heat of fusion (i.e., slight supercooling and rapid accretion). With larger
accretions, the ice shape typically includes “horns” protruding from unprotected leading edge
surfaces. It is the ice shape, rather than the clarity or color of the ice, which is most likely to
be accurately assessed from the cockpit. The terms “clear” and “glaze” have been used for
essentially the same type of ice accretion, although some reserve “clear” for thinner accretions
which lack horns and conform to the airfoil.
Intercycle Ice Ice which accumulates on a protected surface between actuation cycles of a deicing system.
Known or Observed or
Detected Ice Accretion
Actual ice observed visually to be on the aircraft by the flight crew or identified by on−board
sensors.
Mixed Ice Simultaneous appearance or a combination of rime and glaze ice characteristics. Since the
clarity, color, and shape of the ice will be a mixture of rime and glaze characteristics, accurate
identification of mixed ice from the cockpit may be difficult.
Residual Ice Ice which remains on a protected surface immediately after the actuation of a deicing system.
Rime Ice A rough, milky, opaque ice formed by the rapid freezing of supercooled drops/droplets after
they strike the aircraft. The rapid freezing results in air being trapped, giving the ice its opaque
appearance and making it porous and brittle. Rime ice typically accretes along the stagnation
line of an airfoil and is more regular in shape and conformal to the airfoil than glaze ice. It is
　
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