Plain English Meaning

Keeping enough space between the airplane and anything it could hit — like trees, poles, wires, fences, or buildings — as it climbs out or comes in to land.

Full Definition

The vertical and horizontal distance maintained between an aircraft and any terrain, structures, trees, wires, or other obstructions along its flight path, particularly during departure, approach, and landing phases.

Context Anchor

Seen when planning or flying a short-field approach, especially when trees, wires, or rising ground are near the runway end.

Derivation

Obstacle comes from Latin words meaning something that stands in the way. Clearance comes from , meaning free or open. Together, the phrase points to keeping the airplane free of anything in its path, not to getting permission from .