FAA Commercial Pilot Airplane (CAX)Aircraft SystemsMedium
On many retractable landing gear systems, the main gear doors close snugly around the extended wheel after gear extension, then reopen briefly before the gear retracts. What is the primary purpose of this door sequencing?
- ATo provide additional structural support to the extended landing gear
- BTo prevent hydraulic fluid loss during gear cycling
- CTo reduce aerodynamic drag around the extended gear while still allowing clearance for retraction
- DTo trigger the landing gear warning horn when the doors are open
Show answer & explanationAnswer & explanation
Correct answer: C. To reduce aerodynamic drag around the extended gear while still allowing clearance for retraction
Closing the doors around the extended gear streamlines the wheel well opening and reduces drag with the gear down, while reopening the doors before retraction provides the necessary clearance for the gear to swing back into the wheel well. This sequencing is purely aerodynamic and mechanical, not related to structural support, hydraulic sealing, or warning systems.
Why the other options are wrong
- A. Gear doors do not provide structural support to the landing gear itself.
- B. Hydraulic fluid containment is unrelated to door timing.
- D. The gear warning horn is tied to throttle/flap position and gear status, not door position.
Gear Door Sequencing
The timed opening/closing of landing gear doors to reduce drag when gear is extended and provide clearance during retraction.
- Doors close around extended gear to streamline the wheel well
- Doors reopen briefly before retraction begins
- Sequencing is mechanical/hydraulic, tied to gear actuator position
Memory trick: Close for cruise, open to move.