Plain English Meaning
Full Definition
A height measurement expressed as the vertical distance between the aircraft and the terrain directly beneath it. AGL changes as the ground beneath the aircraft rises or falls, even when the aircraft maintains a constant altitude above sea level.
Context Anchor
Seen in weather reports, traffic pattern altitudes, obstacle heights, and low-altitude flying discussions.
Why Pilots Care
Critical for terrain clearance, obstacle avoidance, and meeting minimum altitudes that are not referenced to sea level.