The uplock is a mechanical hook or latch assembly that physically holds the landing gear struts and doors in the retracted position during flight. It carries the weight of the gear assembly so the hydraulic system does not have to remain pressurized. Releasing the uplock is the first step in gear extension, often triggering a free-fall sequence if hydraulic power fails.
Heard on the job
Check the main gear uplock rollers for wear during the walkaround, they were sticking on the last leg.
Insider tip
A failed uplock will cause the gear to drop into the slipstream, drastically increasing drag and forcing an immediate return to the field.