Definition
An autopilot annunciator message indicating that the vertical speed mode has failed or cannot be engaged, typically because the system has detected a fault, lost a required input signal, or cannot capture or hold the commanded rate of climb or descent.
Plain English
A warning on the autopilot panel telling the pilot that the climb-and-descend-at-a-set-rate function isn't working.
Context Anchor
Seen on an autopilot or flight display when using, selecting, or monitoring vertical speed mode during instrument flight.
Why Pilots Care
The pilot must immediately take manual control or select another autopilot mode to prevent unintended altitude changes.
Grounding Statement
This message means the automatic system cannot be trusted to manage how fast the airplane is going up or down.
Intuition Check
Do not read FAIL as meaning the airplane itself has failed or is falling. Here it means a specific automatic flight function is not working correctly.
Example Sentence 1
When VERT SPEED FAIL appeared on the annunciator during the climb, the pilot disconnected the vertical speed mode and selected pitch hold instead.
Example Sentence 2
The crew responded to VERT SPEED FAIL by selecting altitude hold mode to stabilize the flight path.