Icing Intensities And PIREPS

AVIATION WEATHER

CHAPTER FIVE

Icing Intensities And PIREPS

Weather personnel cannot generally observe icing; they must rely on PIREPs. When flying

during icing conditions, pilots should report these conditions as indicated in Figure 5-13.

However, forecasters attempt to forecast the maximum intensity of icing that may be

encountered during a flight, not necessarily the intensity of icing encountered by a particular

aircraft. It becomes the pilot's responsibility to make certain a complete weather briefing is

obtained, to include the information for safe completion of the flight.

Intensity

Airframe Ice Accumulation

Pilot Report

Ice becomes perceptible. Rate of accumulation

Aircraft identification,

Trace

slightly greater than rate of sublimation. It is

location, time (GMT),

not hazardous even though deicing/anti-icing

altitude (MSL), type

equipment is not used, unless encountered for

aircraft, sky cover,

an extended period of time--over one hour.

visibility & weather,

temperature, wind,

The rate of accumulation may create a problem

Light

turbulence, icing, remarks.

if flight is prolonged in this environment (over

Example of PIREP

one hour). Occasional use of deicing/anti-icing

transmission:

equipment removes/prevents accumulation. It

does not present a problem if the deicing/anti-

"Pensacola METRO,

icing equipment is used.

Rocket 501, holding 20

miles south of Navy

The rate of accumulation is such that even short

Moderate

Pensacola, at 2100Z and

encounters become potentially hazardous and

one-six thousand feet,

use of deicing/anti-icing equipment or

single T-39 Sabreliner,

diversion is necessary.

we're IFR in stratus

The rate of accumulation is such that

Severe

clouds, temperature 15C,

deicing/anti-icing equipment fails to reduce or

winds 330 at 25, no

control the hazard. Immediate diversion is

turbulence, Light Rime

necessary.

Icing, flying 200 knots

indicated.

Icing may be rime, clear, or mixed:

Rime ice Rough milky opaque ice formed by the instantaneous freezing of small

super-cooled water droplets.

Clear ice A glossy, clear or translucent ice formed by the relatively slow freezing of

large super-cooled water droplets.

Mixed ice A combination of rime and clear ice.

Figure 5-13 Icing Reporting Criteria

Weather Hazards of Turbulence, Icing, Ceilings, Visibility, and Ash Clouds

5-19