background image

6/17/21 

AIM 

sublimation. A representative accretion rate for 
reference purposes is less than 

¼

 inch (6 mm) per 

hour on the outer wing. The pilot should consider 
exiting the icing conditions before they become 
worse. 

2.  Light. 

The rate of ice accumulation requires 

occasional cycling of manual deicing systems to 
minimize ice accretions on the airframe. A 
representative accretion rate for reference purposes is 

¼

 inch to 1 inch (0.6 to 2.5 cm) per hour on the 

unprotected part of the outer wing. The pilot should 
consider exiting the icing condition. 

3.  Moderate. 

The rate of ice accumulation 

requires frequent cycling of manual deicing systems 
to minimize ice accretions on the airframe. A 
representative accretion rate for reference purposes is 
1 to 3 inches (2.5 to 7.5 cm) per hour on the 
unprotected part of the outer wing. The pilot should 
consider exiting the icing condition as soon as 
possible. 

4.  Severe. 

The rate of ice accumulation is such 

that ice protection systems fail to remove the 
accumulation of ice and ice accumulates in locations 
not normally prone to icing, such as areas aft of 
protected surfaces and any other areas identified by 
the manufacturer. A representative accretion rate for 

reference purposes is more than 3 inches (7.5 cm) per 
hour on the unprotected part of the outer wing. By 
regulation, immediate exit is required. 

NOTE

 

Severe icing is aircraft dependent, as are the other 
categories of icing intensity. Severe icing may occur 
at any ice accumulation rate when the icing rate or 
ice accumulations exceed the tolerance of the 
aircraft.  

EXAMPLE

 

Pilot report: give aircraft identification, location, 
time (UTC), intensity of type, altitude/FL, aircraft 
type, indicated air speed (IAS), and outside air tempera-
ture (OAT). 

NOTE

 

1. 

Rime ice.  Rough, milky, opaque ice formed by the 

instantaneous freezing of small supercooled water 
droplets. 

2. 

C

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

the relatively slow freezing of large supercooled water 
droplets. 

3. 

T

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

included in the PIREP. 

7

1

20.  Definitions of Inflight Icing Terms 

See TBL 7

1

7, Icing Types, and TBL 7

1

8, Icing 

Conditions. 

Meteorology 

7

1

41