Definition
An altitude measured vertically from the surface of the ground directly beneath the aircraft, rather than from sea level. AGL values change as the terrain below the aircraft rises or falls, even when the aircraft maintains a constant altitude above sea level.
Plain English
How high the aircraft is above the ground right below it. If the ground rises, your AGL height drops, even if you haven't climbed or descended.
Context Anchor
Seen in takeoff, landing, traffic pattern, obstacle clearance, and low-altitude flying discussions.
Why Pilots Care
AGL tells a pilot the true height above obstacles and ground, which is essential for safe pattern work, obstacle avoidance, and compliance with minimum altitudes that are stated in AGL.
Grounding Statement
If an airplane is 500 feet AGL, it is 500 feet above the ground below it at that moment.
Intuition Check
Do not read AGL as height above sea level. AGL is height above the ground beneath the airplane.
Example Sentence 1
The pilot leveled off at 1,000 feet AGL to enter the traffic pattern.
Example Sentence 2
During the before-takeoff check the instructor confirmed the student knew the pattern altitude in AGL for the airport elevation.