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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



Pilot report: give aircraft identification, location,

time (UTC), intensity of type, altitude/FL, aircraft
type, indicated air speed (IAS), and outside air
temperature (OAT).


1. Rime ice. Rough, milky, opaque ice formed by the
instantaneous freezing of small supercooled water


Clear ice. A glossy, clear, or translucent ice formed by

the relatively slow freezing of large supercooled water


The OAT should be requested by the FSS or ATC if not

included in the PIREP.



22. Definitions of Inflight Icing Terms

See TBL 7−1−8, Icing Types, and TBL 7−1−9, Icing




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


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

the ice shape, rather than the clarity or color of the ice, which is most likely to be accurately

assessed from the cockpit.

Runback Ice

Ice which forms from the freezing or refreezing of water leaving protected surfaces and

running back to unprotected surfaces.


Ice types are difficult for the pilot to discern and have uncertain effects on an airplane in flight. Ice type definitions will
be included in the AIM for use in the “Remarks” section of the PIREP and for use in forecasting.

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