Define the term 'downlock' in landing gear systems.

• A. A mechanical latch that secures the gear in the fully extended and locked position to prevent retraction.
• B. An electrical sensor that monitors wheel speed.
• C. A hydraulic valve controlling door movement.
• D. A device that senses wing flaps position.

Answer: (A)

Downlock is the mechanical latch that secures the landing gear in the fully extended and locked position, preventing retraction. As the gear lowers and the doors open, a locking mechanism—often a pawl or pin on the gear leg or door frame—engages a receptacle or notch, and spring or gravity helps it stay seated. This lock must withstand the loads of landing, taxiing, and gusts, so the gear remains locked until the retraction sequence is deliberately commanded. When retraction is initiated, hydraulic action releases the lock so the gear can fold into the nacelle or wing.

This isn’t an electrical sensor, a hydraulic valve for door movement, or a flap-position device, so those functions aren’t what the downlock represents.