The Federal Aviation Administration, has identified a risk of sparking in the central fuel tank from suspected premature wearing of bearings while it is empty. The FAA order could disrupt the operation of the extended- range 747-400, causing airlines to introduce a refuelling stop or carry lighter loads to maintain aircraft range.
Normally, the pumps in both the horizontal stabiliser tank and centre tank are run until the tank is dry in order to use up the fuel efficiently. Fuel in excess of that needed for the journey cuts into profits. The FAA asked operators to leave enough fuel in the centre tank of all 747 models and cease using the horizontal stabiliser tank in the rear of the 747-400 to prevent pumps overheating while the erosion of bearings is investigated.
"Operated in dry conditions ... this metal-on-metal contact could cause hot spots and sparks, and a possible explosion." the FAA said in a statement. Boeing Co. spokesman Russ Young disputed the risk of an explosion. "We've done tests with those pumps, and we're convinced this problem would not ignite fuel vapour." he said. Mr Young said Boeing was working as quickly as it could to resolve the bearing problem so the 747-400 horizontal stabiliser tanks could be used again.