New Definitions for Icing PIREPs

The February 9, 2012 edition of the AIM includes an update to section 7-1-21: PIREPS Relating to Airframe Icing. According to the FAA:

This change addresses the change to the icing intensity definitions, quantifiable icing rates, and an updated replacement for current terminology. It would also help satisfy NTSB Safety recommendations A­96­51 and ­060.

The updated definitions are:

1. Light. The rate of ice accumulation requires occasional cycling of manual deicing systems** to minimize ice accumulations on the airframe. A representative accumulation rate for reference purposes is 1/4 inch to one inch (0.6 to 2.5 cm) per hour (See TBL 7-1-7)  on the unprotected part of the outer wing. The pilot should consider exiting the condition.

2. Moderate. The rate of ice accumulation requires frequent cycling of manual deicing systems** to minimize ice accumulations on the airframe. A representative accumulation rate for reference purposes is 1 to 3 inches (2.5 to 7.5 cm) per hour (See TBL 7-1-7)  on the unprotected part of the outer wing. The pilot should consider exiting the condition as soon as possible.

3. Heavy.  The rate of ice accumulation requires maximum use of the ice protection systems to minimize ice accumulations on the airframe. A representative accumulation rate for reference purposes is more than 3 inches (7.5 cm) per hour (See TBL 7-1-7)  on the unprotected part of the outer wing. Immediate exit from the conditions should be considered.

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. Immediate exit from the condition is necessary.

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