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7-1-22. Definitions of Inflight Icing Terms
See TBL 7-1-6, Icing Types, and TBL 7-1-7, Icing
Conditions.
TBL 7-1-6
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
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.
Note-
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.
2/14/08 AIM
Meteorology 7-1-43
TBL 7-1-7
Icing Conditions
Appendix C Icing Conditions Appendix C (14 CFR, Part 25 and 29) is the certification icing condition standard
for approving ice protection provisions on aircraft. The conditions are specified in
terms of altitude, temperature, liquid water content (LWC), representative droplet
size (mean effective drop diameter [MED]), and cloud horizontal extent.
Forecast Icing Conditions Environmental conditions expected by a National Weather Service or an
FAA-approved weather provider to be conducive to the formation of inflight icing
on aircraft.
Freezing Drizzle (FZDZ) Drizzle is precipitation at ground level or aloft in the form of liquid water drops
which have diameters less than 0.5 mm and greater than 0.05 mm. Freezing drizzle
is drizzle that exists at air temperatures less than 0C (supercooled), remains in
liquid form, and freezes upon contact with objects on the surface or airborne.
Freezing Precipitation Freezing precipitation is freezing rain or freezing drizzle falling through or outside
of visible cloud.
Freezing Rain (FZRA) Rain is precipitation at ground level or aloft in the form of liquid water drops which
have diameters greater than 0.5 mm. Freezing rain is rain that exists at air
temperatures less than 0C (supercooled), remains in liquid form, and freezes upon
contact with objects on the ground or in the air.
Icing in Cloud Icing occurring within visible cloud. Cloud droplets (diameter < 0.05 mm) will be
present; freezing drizzle and/or freezing rain may or may not be present.
Icing in Precipitation Icing occurring from an encounter with freezing precipitation, that is, supercooled
drops with diameters exceeding 0.05 mm, within or outside of visible cloud.
Known Icing Conditions Atmospheric conditions in which the formation of ice is observed or detected in
flight.
Note-
Because of the variability in space and time of atmospheric conditions, the existence
of a report of observed icing does not assure the presence or intensity of icing
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