Definition
An aircraft system that warns the pilot, by visual and/or aural signal, when the airplane is approaching a preselected altitude or has deviated from it by more than a set tolerance. Required equipment on most turbojet-powered civil airplanes under 14 CFR.
Plain English
A device the pilot dials a target altitude into. It sounds a tone or flashes a light when the airplane is nearing that altitude, and again if the airplane drifts away from it after leveling off.
Context Anchor
Seen in aircraft with more advanced flight instruments, especially when climbing, descending, leveling off, or maintaining an assigned altitude.
Derivation
Altitude comes from the Latin altus, meaning “high.” Alert comes from an older military phrase meaning “on watch” or “ready.” Together, the term points to a system that watches the aircraft’s height and gets the pilot’s attention at the right time.
Why Pilots Care
Reduces the chance of unnoticed altitude deviations that violate ATC clearances or create traffic conflicts.
Intuition Check
An altitude alerting system does not fly the airplane to the selected altitude by itself. It warns the pilot about altitude; it does not necessarily control altitude.
Example Sentence 1
After being cleared to climb to 24,000 feet, the captain set 24,000 in the altitude alerter and watched for the approach tone.
Example Sentence 2
During the descent the pilot armed the altitude alerting system for the next assigned level.