Ramon Lopez/WASHINGTON DC
Boeing 747 fuel pumps are to be subjected to additional compulsory checks because excessive wear, which could cause arcing leading to fire, has been discovered.
The US Federal Aviation Administration is taking a rigorous view of the issue in light of the July 1996 Trans World Airlines 747-100 explosion. It has issued an airworthiness directive (AD) ordering inspection of the inlet check valves and inlet adapters in centre wing fuel tank (CWT) pumps on all 747s which recorded more than 20,000 in-service hours. Routine airline inspections of the aircraft's fuel tanks have revealed excessive wear on the inlet adapters of the override/jettison pumps on some 747s, allowing contact between the check valve and inducer, which could produce arcing.
The AD also introduces new regulations - applicable to 747s with more than 20,000h - for the handling of fuel carried in the CWT (the empty tank which was known to have exploded in the TWA 800 event as a result of the ignition of fuel vapour).
Advising pilots of the hazards of "dry operation" of the pumps, the AD specifies that they must not be used if there is less than 3,200kg (7,000lb) of fuel in the CWT, indicating that, if the CWT scavenge pumps are inoperative, that fuel is effectively unusable.
Following reports of engine fuel pump control shaft problems on all jets powered by Pratt & Whitney JT8D turbofans, the US National Transportation Safety Board has recommended that the FAA should order their regular inspection and ultimate modification. Types affected include McDonnell Douglas DC-9s and Boeing 727s, 737s and MD-80s.
Source: Flight International
