Definition
A condition in which the landing gear has been fully extended and mechanically secured in the down position, with the over-center linkage or downlock mechanism engaged so the gear will not collapse under the weight of the aircraft on touchdown.
Plain English
The wheels are all the way down and held there by a mechanical lock, so they will not fold up when the aircraft lands.
Context Anchor
Used during landing checks and during troubleshooting when a landing gear problem is suspected.
Why Pilots Care
Extended is not the same as locked. Gear that is down but not locked can collapse on touchdown. Confirming 'down and locked' — usually by three green indicator lights or a mechanical position indicator — is the final check before landing.
Intuition Check
Do not assume “down” means safe by itself. For landing gear, the important condition is both down and locked: fully extended and secured in place.
Example Sentence 1
After lowering the gear on downwind, the pilot checked for three green lights to confirm the gear was down and locked.
Example Sentence 2
After using the emergency extension handle, the indicators finally showed the gear was down and locked.