NTSB Safety Alert on Operating Aircraft in Icing Conditions

The U.S. National Transportation Safety Board (NTSB) has issued a Safety Alert, directed to pilots, about operating aircraft in icing conditions. The Safety Alert is intended to increase the visibility of airplane icing issues and "address procedures taught regarding the accumulation of ice before activating deice boots," according to NTSB Acting Chairman Mark V. Rosenker.

Some of the highlights of the newly issued Safety Alert, which was approved by all five Board Members, are:

• noting that as little as 1/4 inch of ice can be deadly;
• as little as 1/4 inch of leading edge ice can increase the stall speed 25 to 40 knots; and
• early activation of the deice boots limits the effects of leading-edge ice and improves the operating safety margin.

The Safety Alert states that leading-edge deice boots should be activated as soon as icing is encountered, unless the aircraft flight manual or the pilot's operating handbook specifically directs not to activate them.

In the Alert, pilots are instructed to maintain extremely careful vigilance of airspeed and any unusual handling qualities if the aircraft manual or the pilot's operating handbook allows for an accumulation of ice before activating the deice boots, and to turn off or limit the use of the autopilot in order to better "feel" changes in the handling qualities of the airplane.

Here is the link to the Safety Alert: Aircraft Ground Icing - NTSB, 2-page 'pdf' file