What happened
During the retraction of the landing gear, the 'A' hydraulic system was lost. The failure occurred when the left main gear door up line ruptured at a point where it had been subjected to chafing from the Auxiliary Power Unit (APU).
In response to the failure, the captain ordered the dumping of 30,000 pounds of fuel, followed by an attempt to manually extend the landing gear. The flight engineer attempted to perform the manual extension but was unable to get the right main gear to extend. The captain instructed the flight engineer to check the position of the main landing gear through the cabin view ports; however, the flight engineer could not locate these ports and returned to the cockpit.
The captain subsequently ordered the fuel to be dumped until it reached a minimum level. An approach and landing were then conducted with the right main gear in a retracted position.
The investigation
Following the landing, the aircraft was raised to inspect the landing gear. Upon inspection, the right main landing gear was found to be stowed on the uplock in its normal position. The gear was then successfully extended using standard manual extension procedures. Investigators found no evidence of a mechanical malfunction within the right main gear itself.