DALLAS — The U.S. Federal Aviation Administration (FAA) is adopting a new airworthiness directive (AD) for certain Boeing 747-400 and 747-8 aircraft after reports of wear-through of components of the transfer pump for the horizontal stabilizer fuel tank.
The FAA document states that the wear-through is caused by contact between the pump’s inlet check valve and the inlet adapter. Specifically, the AD requires inspecting for wear of the motor impeller inlet check valves and inlet adapters of the transfer pumps for the horizontal stabilizer fuel tank and doing corrective actions, if necessary.
The AD addresses the development of an ignition source within the horizontal stabilizer fuel tank as a result of the aforementioned wear-through. According to the FAA, this condition, in combination with flammable fuel vapors, could result in a fuel tank explosion and the consequent loss of the airplane.
Thus, the FAA issued the AD because it had determined the unsafe condition described previously was “likely to exist or develop in other products of the same type design.”
The largest U.S. operator of the Boeing 747-8F is Louisville, Kentucky-based UPS Airlines (5X), with 28 aircraft. The cargo airline also operates 13 Boeing 747-400F. That’s 41 cargo variants of the Jumbo jets addressed in the AD.
Cost of Part Inspections, Replacement
The FAA estimates that this AD will affect 28 aircraft registered in the United States and that the cost for U.S. operators to comply with the AD is more than $50,000, including inspections and replacement of the aforementioned components. However, the aviation authority was clear that it had no way of determining the number of aircraft that might require such replacements.
In a similar move, the FAA requested two weeks ago that Airbus make some changes to the fuselage of the A321XLR as it relates to the aircraft’s Rear Center Tank (RCT), claiming that the tank needed to be redesigned to avoid serious fire risks in the event of a survivable crash.
You can read the full FAA Boeing 747-400/-8 docket here. The document is scheduled to be published in the Federal Register on 12/29/2022 and available online at federalregister.gov/d/2022-28386, and on govinfo.gov.
Featured image: Boeing 747-8 (house colors). Photo: Brandon Farris/Airways