In a hydraulically actuated landing gear extension, what is the correct standard sequence?

• A. Hydraulic pressure is applied to gear actuators, gears rotate down from stowed position, doors open to clear the gear path, gear fully extends and locks, doors close to streamline the gear, and down-lock indicators confirm full extension.
• B. Gears rotate down from stowed position, hydraulic pressure is applied to actuators, doors close to streamline, gear fully extends and locks, doors open to clear the gear path, and down-lock indicators confirm full extension.
• C. Doors open to clear the gear path, hydraulic pressure is applied to actuators, gears rotate down from stowed position, gear fully extends and locks, doors close to streamline, and down-lock indicators confirm full extension.
• D. Hydraulic pressure is applied to actuators, doors open to clear the gear path, doors close to streamline, gear rotates down, gear fully extends and locks, and down-lock indicators confirm extension.

Answer: (A)

In hydraulically actuated landing gear extension, the system is designed so energy is applied first to start moving the gear, and then the surrounding doors and locks coordinate in a safe sequence. Applying hydraulic pressure to the gear actuators starts the motion, moving the gear down from its stowed position. As the gear begins to move, the doors open to clear the gear path so there is no interference with the gear as it extends. The gear then fully extends and locks into the down position, providing a secure configuration for landing. After locking, the doors close to streamline the gear and reduce drag, and down-lock indicators confirm that the gear is fully extended and locked in place.

This sequence ensures there’s always clearance for the gear to move without the doors obstructing it, and that a reliable lock is established before the doors are sealed, giving the crew a positive indication that the gear is safely deployed.