Plain English Meaning

An instrument that bounces a radio signal off the ground to tell the pilot exactly how high the aircraft is above the terrain right beneath it.

Full Definition

An aircraft instrument that measures height above the terrain directly below the aircraft by transmitting a radio signal toward the ground and timing how long it takes for the reflected signal to return. It provides absolute altitude (height above ground) rather than altitude above sea level, and is most accurate at low altitudes, typically up to 2,500 feet AGL.

Context Anchor

Seen in low-altitude operations, instrument approaches, callouts, terrain warning , and some landing or functions.