Definition
Hinged panels on the underside of the aircraft that cover the wheel wells when the landing gear is retracted, forming a smooth, flush surface with the surrounding skin to reduce aerodynamic drag. On most retractable-gear airplanes the doors open during the gear extension and retraction cycle and close again once the gear is fully up or fully down.
Plain English
Small hinged covers that close over the openings where the wheels go when the gear folds up, so the bottom of the aircraft stays smooth in flight.
Context Anchor
Seen during preflight checks, landing gear system discussions, and any time a pilot is confirming that retractable landing gear is moving normally.
Derivation
In aviation, “gear” is short for “landing gear,” the wheels and supporting parts the airplane uses on the ground. “Doors” keeps its normal meaning: panels that open and close. Together, “gear doors” means the panels that open and close for the landing gear.
Why Pilots Care
Improper gear door operation increases drag, raises fuel use, or risks damage to the landing gear mechanism.
Intuition Check
Do not read “gear” here as general equipment or tools. In this term, “gear” means landing gear: the wheels, struts, and related parts used for takeoff, landing, and ground movement.
Example Sentence 1
After takeoff and gear retraction, the gear doors closed flush with the fuselage, and the airplane accelerated as drag dropped.
Example Sentence 2
During the preflight the mechanic checked that the gear doors aligned and sealed correctly.