Which icing condition is prohibited from flight?

• A. Moderate icing
• B. Severe icing
• C. Light icing
• D. Severe or structural icing

Answer: (D)

In-flight icing is limited by what the aircraft is certified to handle. The categories describe how much ice can accumulate and where it can form on the airplane. Severe icing means ice buildup that progresses rapidly and cannot be controlled, and structural icing refers to ice on critical surfaces of the airframe that would compromise lift, handling, or structural integrity. These conditions are outside the approved operating envelope, so flight into severe or structural icing is prohibited.

Light and moderate icing are considered within the allowable envelope when procedures and de-ice/anti-ice systems are used as required, so they may be encountered under guidance. Therefore, the condition that must be avoided entirely is severe or structural icing.