Definition
An annunciation displayed by the autopilot or flight director system indicating that valid airspeed data is no longer being received from the air data computer or pitot-static system. When this fails, autopilot modes that depend on airspeed (such as IAS hold or speed-based pitch modes) become unreliable or are automatically disengaged.
Plain English
A warning that the autopilot has lost a working airspeed signal. Any autopilot function that needs to know the airplane's speed can no longer be trusted, and the pilot must take over those tasks manually.
Context Anchor
Seen on a flight display or autopilot-related alert area when the aircraft’s airspeed information becomes invalid or unavailable.
Why Pilots Care
The autopilot typically reverts to a safe default mode or disconnects to avoid unsafe pitch commands without valid speed data.
Intuition Check
AIRSPEED FAIL does not mean the airplane has stopped moving through the air. It means the system that reports airspeed has failed or is giving unusable information.
Example Sentence 1
When the AIRSPEED FAIL annunciation appeared, the pilot disconnected the autopilot and continued the climb manually using pitch and power.
Example Sentence 2
The AIRSPEED FAIL warning cleared once the blocked pitot tube was cleared and airspeed data returned.