Definition
The fully extended position of retractable landing gear in which the gear legs are mechanically locked into place by an internal locking mechanism (typically an over-center linkage), allowing the gear to support the weight of the airplane on landing without collapsing.
Plain English
The landing gear is all the way down, and a mechanical lock has clicked into place to hold it there so it cannot fold up when the airplane touches the ground.
Context Anchor
Seen in retractable-landing-gear airplanes during before-landing checks, landing gear indications, and go-around or rejected-landing procedures.
Derivation
Combines 'down' for the extended direction with 'locked' for the mechanical safety latch that prevents retraction.
Why Pilots Care
Confirms the aircraft can land safely without risk of gear collapse.
Intuition Check
Do not read this as just “the gear handle is down.” It means the landing gear itself is fully extended and secured in place.
Example Sentence 1
After lowering the gear on downwind, she waited for three green lights to confirm the gear was in the down-and-locked position before continuing the approach.
Example Sentence 2
After lowering the gear on the go-around checklist, the student confirmed the down-and-locked position by checking the indicator lights.