Which components are responsible for sequencing during gear extension and retraction?

• A. Door interlocks and sequencing valves ensure doors and gear move in the correct order to prevent interference.
• B. Oleo struts adjust wheel alignment.
• C. Weight-on-wheels devices control runway lighting.
• D. Shimmy dampers guide steering wheel.

Answer: (A)

During gear extension and retraction, the sequence of moves must be tightly coordinated to avoid anything colliding—doors, gears, and wheels must move in a safe order. This coordination is achieved mainly through door interlocks and sequencing valves. Door interlocks physically prevent doors from moving unless the gear is in a safe position (and vice versa), ensuring doors don’t collide with a deploying or stowing gear. Sequencing valves control hydraulic pressure to the different actuators in the correct order, so doors open first to clear the path, then the gear extends and locks, and on retraction the sequence reverses with gear stowing before doors close. This combination guarantees that each step occurs only when the previous one is complete, preventing interference and ensuring a safe, reliable cycle.

The other components don’t manage this order. Oleo struts handle shock absorption and wheel/cycle alignment rather than the timing of door and gear movements. Weight-on-wheels devices signal ground contact for systems like braking or control logic, not gear sequencing. Shimmy dampers reduce steering wheel oscillations, not the order of gear extension or retraction.