The Flight 800 Investigation

WASHINGTON — Federal regulators on Wednesday ordered operators to make safety adjustments to the fuel tanks of more than 400 Boeing 767s registered in the U.S. in order to prevent a devastating midflight explosion.

The safety directive issued by the Federal Aviation Administration gives operators of the popular airliner three years to install an automatic fuel pump shut-off system for the center fuel tanks on 767s. The concern is that if fuel in the tanks becomes too low while the pump is still operating, under certain conditions it could ignite fuel and air vapors, causing an explosion.

In the meantime, flight crews are supposed to shut-off the pumps themselves when fuel gets low.

The estimated fleetwide cost of complying with the order is $4.6 million.

Boeing spokeswoman Liz Verdier said the Chicago-based aircraft manufacturer sent operators of 767s a service bulletin two years ago recommending the changes in20Wednesday's FAA order. Compliance with service bulletins is voluntary. Verdier said she didn't know how many operators may have already installed the automatic shut-off systems.

FAA has no authority to order foreign carriers operating 767s to install the shut-off systems, but most operators usually comply voluntarily or are ordered to do so by aviation authorities in their countries. There are about 960 of the 767s in operation worldwide, including 414 in the U.S., Verdier said.

The latest order is one of a lengthy series of steps taken in the last decade to prevent the possible ignition of vapors inside fuel tanks in response to the explosion of TWA Flight 800 off the coast of New York's Long Island in 1996. All 230 people on board the Boeing 747 were killed.