| WASHINGTON - 12/03/98
The Federal Aviation Administration (FAA) today
ordered operators of Boeing 747 aircraft to immediately
change fuel pump procedures to prevent "dry
operation" that could result in ignition of the
center fuel or horizontal stabilizer tanks. This is an
interim action while the FAA and The Boeing Company
determine the cause of premature wear on some pump shaft
bearings.
The FAA's Airworthiness Directive (AD) follows recent
reports of pump failures due to premature wear of the
shaft bearing. Operated in dry conditions, in which the
parts are not covered by fuel, rotating parts could rub
against other non-rotating parts. This metal-on-metal
contact could cause hot spots and sparks, and a possible
explosion. Therefore, the FAA has ordered operators to:
Cease operation of the horizontal stabilizer tank on
Boeing 747-400 series aircraft. Normally, the pumps in
the horizontal tank are run until the tank is dry.
Maintain a certain minimum level of fuel when using the
center fuel tank on Boeing 747s. The pumps on these tanks
are normally operated until the fuel in the tank is
exhausted and the pump inlet is uncovered, exposing the
pump to dry operation for a period of time during each
flight that uses the center tank. The AD gives operators
two options to prevent dry operation when using the
center fuel tank. One procedure requires a minimum of
17,000 lbs. of fuel in the center tank before flight. The
pumps must then be shut off when no less than 7,000 lbs.
of fuel is left in the tank. Alternatively, a minimum of
50,000 lbs. of fuel must be loaded before flight with a
shutoff point of 3,000 lbs. In both situations, the
scavenge fuel pumps will continue to transfer fuel from
the tank but at a slower rate. Both procedures depend on
the duration of the flight.
There are approximately 700 suspect bearings in new and
overhauled pumps, and part kits. The pumps normally
operate for at least 20,000 hours before removal. The
recently discovered problem pumps had only been operating
for 200 hours.
This AD is unrelated to TWA-800 accident, which is still
under active investigation by the National Transportation
Safety Board. The wear conditions were not found on the
center wing fuel tank override/jettison pumps that were
recovered from that accident.
Worldwide there are 1,087 Boeing 747s in operation, 246
of which are U.S.-registered. Several major U.S.
passenger and cargo airlines are affected by this AD. The
cost to U.S. operators has not been determined.
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