Boeing 767s must be operated with at least 450kg of fuel in their centre-wing fuel-tanks to help prevent an explosion caused by the ignition of fuel vapour, according to a new US Federal Aviation Administration airworthiness directive (AD).

A centre-wing fuel-tank explosion is suspected as the cause of the crash of a Trans World Airlines Boeing 747 off Long Island, New York, in July 1996.

The FAA issued the directive after reading a report describing how a fuel pump failed following damage to an impeller unit and pumping-unit housing caused by a loose diffuser ring in the fuel-pump assembly.

The report is believed to refer to a Royal Brunei 767 leaving Kansai earlier this year. The FAA fears that such a failure could result in sparks inside the fuel tank caused by metal-to-metal contact during dry fuel-pump operation.

The issue had previously been addressed by an AD released three years ago which required repetitive inspections of the pumping-unit assembly to check the tightness of screws.

Relief was allowed if a fuel-pump modification was carried out. The recent failure occurred on a modified unit, however.

The FAA says that keeping 450kg of fuel in the centre tank will preclude fuel-vapour ignition, even if the fuel pump does fail.

The AD applies to 767s only.

Source: Flight International