The FAA issued a statement saying that while this type of wear was not found in the TWA 747 that exploded just after takeoff from New York, officials are trying to minimize future explosions from occurring in the same locations on the planes.
The central fuel tank has been a center of focus since the crash. The concern is that badly worn pumps, situated in the back wall of these 'emergency' or 'jettison' tanks, could collide and cause a fire or explosion.
Excessive dryness in these tanks is also a concern. As a result, until the inspections are made, airlines are directed to keep at least 1,000 gallons of fuel in the tank. The FAA also ordered revision of 747 flight manuals to ensure flight crews are aware of restrictions on running the jettison pumps in a dry tank.
"If the center tank override/jettison fuel pumps are to be used, there must be at least 17,000 pounds (7,720 kg) of fuel in the center tank prior to engine start," the FAA's directive states.
An FAA airworthiness directive issued Friday called for examination of the inlet check valves and jettison pumps on all 747 aircraft and installation of replacement parts if necessary after two instances of wear were found in a 747-400 series plane. All inspections are expected to be done within two weeks of August 24th.
The FAA order affects about 300 U.S.-registered 747 aircraft. U.S. operators affected include Continental Airlines, FedEx, United Airlines, Northwest Airlines and UPS. Boeing says there is no way the worn parts could cause an explosion, but the order leaves airlines no choice.
Foreign aviation regulators are likely to follow the FAA lead for the 800 or so 747s elsewhere in the world.
The estimated cost to comply with the airworthiness directive is $216,000 for the entire U.S. fleet.