Boeing 747 fuel pump problem

Boeing 747 fuel pump problem

Keywords Boeing,Fuels, Pumps

Although tribological issues are no doubt uppermost in the minds of the majority of the readers of this journal, it is unusual that such incidents achieve exposure in the international media. However, as we go to press, we learn that some airline operators of Boeing 747s are assessing the possible effects on their long-range schedules of a US Federal Aviation Administration emergency Airworthiness Directive which effectively places limitations on their quantities of usable fuel. This requirement has emerged following the discovery by one 747 operator of premature wear in a number of fuel tank pumps from centre-wing tanks. These particular pumps were associated with the override/jettison fuel tanks. The worn bearings resulted in axial shift of the steel paddle wheel, allowing contact with the pump end plates. This in turn would cause the pump circuit breakers to trip which according to the FAA could constitute an ignition risk. The directive requires that the fuel pumps are switched off before the tanks are empty, and it also bans the use of the horizontal-stabiliser fuel tanks. Although no scheduling changes have been announced by European airlines, certain transPacific operators, including Cathay Pacific and Northwest airlines, are planning for contingency stops in Anchorage on some US-Asia routes.

The FAA has stated that this directive is not related to the investigation of the 1996 Trans World Airlines 747-100 accident near Long Island, New York, where the centre-wing fuel tank unaccountably exploded with disastrous consequences. However, one is still left with the suspicion of the possibility that one of the worst aviation accidents in history could have been caused by a basic tribological problem.