Plain English Meaning
The wheels are all the way down and held there by a mechanical lock, so they will not fold up when the aircraft lands.
Full 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.
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.