Definition
Any visual, aural, or tactile signal that an aircraft system is not operating correctly. Common indications include warning lights, abnormal instrument readings, unusual sounds, vibrations, smells, or unexpected aircraft behavior that alert the pilot to a malfunction requiring assessment and action.
Plain English
A sign that something on the aircraft has broken or is not working as it should. The sign could be a light, a strange instrument reading, a noise, a smell, or the way the aircraft is flying.
Context Anchor
A pilot may see this during preflight, engine start, taxi, flight, or shutdown when checking instruments, lights, sounds, and aircraft behavior.
Why Pilots Care
Early recognition lets the pilot respond promptly to maintain control and avoid escalation into an emergency.
Intuition Check
Do not assume an indication of system failure always means a complete failure has already happened. In aviation, it means there is a sign that something may be wrong and the pilot must treat it seriously until confirmed otherwise.
Example Sentence 1
The flickering oil pressure gauge was the first indication of system failure, prompting the pilot to divert to the nearest airport.
Example Sentence 2
The pilot scanned the panel for any indication of system failure before continuing the approach.