The Federal Aviation Administration (FAA) has issued an Airworthiness Directive (AD) ordering airlines to make safety modifications to the fuel tanks of over 400 Boeing 767 aircraft. The AD is designed to prevent fuel tank explosions. The latest AD is one of a lengthy series of steps taken in the last decade to prevent the possible ignition of vapors inside fuel tanks. They are 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. The safety directive gives B-767 operators three years to install an automatic fuel pump shutoff 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.