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. 

