The Federal Aviation Administration has issued an airworthiness directive (AD) for positive Boeing 747 following protection worries approximately a pump inside the aircraft’s horizontal stabilizer gas tank.
The AD, which became posted on the National Register on December 29, will take effect on January 13, 2023.The FAA says it influences 28 Boeing 747-400 series and 747-8 series currently.
“This AD changed by way of reviews of wear-via of the motor impeller inlet adapter of a switch pump for the horizontal stabilizer gas tank as a result of touch between the pump inlet test valve and the inlet adapter,” the FAA writes. The AD calls this a “hazardous condition” that could require inspections and feasible alternatives to the inlet test valves and adapters of the switch pumps.
The problem was discovered while operators were “troubleshooting gas imbalance issues with the primary wing gas tanks, which use the identical pump layout as the horizontal stabilizer gas tank.”
So far, Boeing has discovered pumps with wear “enough to permit touch between the motor impeller inlet test valve flapper and the pump inducer,” in addition to 22 more severely worn pumps. The inlet test valve can vibrate so much that it is able to create metal-on-metal contact, inflicting friction and heat, and possibly creating a spark within the gas tank.
“This condition, combined with flammable gas vapors, should result in a gas tank explosion and, as a result, the loss of the airplane,” the AD says.
The FAA estimates that the inspections will cost operators just over $30,000 per plane, and that changing the inlet adaptor and test valve will cost about $23,000 per plane.
Cirium Fleets data show that 94 747- 400s and 41 747-8s are currently registered in the United States. The majority of these planes fly for Atlas Air, Kalitta Air, UPS Airlines, and FedEx