Definition
Mechanical devices on retractable landing gear that secure each gear leg in the fully extended position, preventing it from collapsing or retracting under the loads of landing, taxi, and takeoff roll.
Plain English
Latches that hold the wheels rigidly in the down position so the gear can't fold up when the airplane's weight settles on it.
Context Anchor
You encounter downlocks when studying retractable landing gear systems, landing gear position indications, and abnormal landing gear procedures.
Derivation
Plain compound of 'down' (the gear position) and 'lock' (a device that holds something in place). The name describes its job: it locks the gear down.
Why Pilots Care
They keep the gear from collapsing on landing or during taxi, directly protecting the aircraft structure and occupants.
Analogy
Think of a folding table leg that must snap into its locked position before the table can hold weight. The leg being extended is not enough; it also has to be locked.
Grounding Statement
For landing gear, down and locked means the gear is extended and the downlocks are holding it there.
Intuition Check
Do not assume the gear is safe just because the gear handle is down or the wheels appear extended. Downlocks are what confirm the gear is held in the landing position.
Example Sentence 1
After lowering the gear, the pilot waited for three green lights to confirm the downlocks had engaged.
Example Sentence 2
During the emergency gear extension, the downlocks snapped into place with an audible click.