Definition
A backup method built into an aircraft's retractable landing gear that allows the pilot to lower the gear when the normal extension system has failed. Depending on the aircraft, this system may use a hand crank, a hand pump, gravity (free-fall), compressed gas (such as nitrogen or CO2), or a redundant hydraulic or electric circuit to extend and lock the gear in the down position.
Plain English
A backup way to get the wheels down if the regular system stops working. Different aircraft use different methods, but the goal is the same: get the gear down and locked so a normal landing is possible.
Context Anchor
Encountered in retractable-gear airplane training, especially during emergency procedures and before-landing checks.
Why Pilots Care
Allows the aircraft to land with the gear extended instead of on its belly, reducing structural damage and preserving directional control on rollout.
Analogy
It is like having a manual way to open an electric garage door when the power fails. The normal system is preferred, but the backup lets you finish the job safely.
Intuition Check
“Gear” here means landing gear—the wheels and supporting parts used for takeoff and landing. “Extension” here means moving the landing gear down into the landing position, not making it longer.
Example Sentence 1
When the gear-down light failed to illuminate, the pilot followed the checklist and used the emergency gear extension system to lower and lock the wheels.
Example Sentence 2
The checklist called for the emergency gear extension system if normal gear-down indications were not received before landing.