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

Meteorology

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 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 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.

7-1-41