Definition
The manufacturer-specified backup methods used to lower the landing gear when the normal extension system fails. These procedures vary by airplane and may include a manual hand crank, a hydraulic hand pump, a CO2 blowdown bottle, a free-fall release that lets gravity pull the gear down, or a combination of these. The exact steps, airspeed limits, and confirmation checks are published in the Pilot's Operating Handbook (POH) or Airplane Flight Manual (AFM) for that specific airplane.
Plain English
If the normal way of putting the wheels down doesn't work, these are the backup steps the manufacturer gives you to get the gear down another way -- by hand crank, hand pump, gas bottle, or just letting gravity drop it. The exact steps are in the airplane's handbook.
Context Anchor
You encounter these procedures in the airplane's operating handbook, during training in retractable-gear airplanes, and during an approach if the gear does not show safely down.
Derivation
Extension comes from older Latin-based words meaning to stretch or spread out. In this aviation use, it does not mean making the landing gear longer; it means moving the gear out of its retracted position into the down position for landing.
Why Pilots Care
A successful landing with the gear down prevents aircraft damage, reduces the risk of fire or injury, and avoids the need for a gear-up emergency landing.
Intuition Check
Do not assume “emergency extension” means improvising a way to force the gear down. It means following the airplane's published backup checklist for lowering and locking the gear when the normal system fails.
Example Sentence 1
When the gear handle was selected down and no green lights appeared, the pilot pulled out the POH and began the landing gear emergency extension procedures.
Example Sentence 2
The emergency checklist directed the use of the hand pump as part of the landing gear emergency extension procedures to ensure the main gear locked into place.