Plain English Meaning

A device in the cockpit that lets you set the altitude you want to fly at, then beeps or flashes to tell you when you're getting close to it and again if you accidentally climb or descend away from it.

Full Definition

A cockpit instrument that warns the pilot when the aircraft is approaching or deviating from a preselected altitude. The pilot dials in the target altitude, and the alerter provides visual and/or aural signals as the aircraft nears that altitude and again if it drifts away from it after capture.

Context Anchor

Used during climbs, descents, and level-offs, especially in instrument flying when the pilot must capture and maintain assigned altitudes accurately.

Derivation

Altitude comes from the Latin altus, meaning high. comes from an old warning sense meaning watchful or on guard. Together, altitude alerter means a that keeps watch a selected height.