Every type of retractable landing gear requires ground locks in addition to the normal protection given by over-centre devices. The over-centre links hold the gear locked down, but with the absence of hydraulic pressure, this can not be absolutely guaranteed. Thus, the landing gear down-locks ensure that accidental retraction can not occur, when the aircraft is on the ground.

Ground locks comprise either:

• Locking pins inserted at key pivot points in the main gear and nose gear once the aircraft has parked. This makes absolutely sure that the gear can not collapse if the aircraft is moved.
• Clamps, which clamp around the actuator of the main retraction jacks, thus preventing them from retracting.

If the Pilot forgets to remove the pins or locks before flight, the helicopter will be unable to retract the gear after take-off. To reduce this risk, a large red "REMOVE BEFORE FLIGHT" flag is normally attached to each pin or lock.

The ground locks are normally carried in a prominent position on-board, so that the crew can quickly confirm that all the locks have been removed before flight.