Boeing 747-400 Landing Gear tests

After replacing a damaged landing gear door, the one attached to the landing gear strut, it was necessary to check the alignment of the door when closed. The only way to do that is to raise the gear.

Instead of jacking the aircraft off the ground, jacks are placed at the specified locations and then special floor sections in the hangar can be lowered. The aircraft is still sitting on three main and one nose leg. Gear down lock pins stop those legs from trying to retract when the lever in the cockpit is moved to the gear up position.

The first "lift" was accomplished using an electric motor driven hydraulic pump, although this type of pump can produce the required pressure, it has a vastly lower flow rate than engine driven or air driven pumps. This is beneficial for the first test however, the gear travels slowly and can be stopped quickly in the event of a problem. That low flow rate is most evident when the leg is being extended.

The second test was performed using an air driven pump. An external air supply is plugged into the aircraft to pressurise it's pnuematic ducts, the air driven pump provides the same pressure as the electric one but can maintain a much higher flow rate. This can be seen in the video as a much smoother retraction and extension of the gear.

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