background image

AIM 

6/17/21 

TBL 7

1

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. 

7

1

42 

Meteorology