If the Landing gear selector valve fails to stay down when depressed, which system will be unavailable unless the valve is held in the down position?

• A. Nose Wheel Steering
• B. Flaps
• C. Elevators
• D. Ailerons

Answer: (A)

The system at stake is the nose wheel steering. The landing gear selector valve routes hydraulic pressure to the nose wheel steering actuator when the gear is down. If the valve doesn’t stay down, the hydraulic path is not maintained once you release the switch, so steering the nose wheel loses power and becomes unavailable unless you physically hold the valve in the down position. Flaps, elevators, and ailerons have their own hydraulic or mechanical power paths and are not dependent on that valve being held down, so they remain usable.