In a move to prevent fuel tank fires, the Federal Aviation Administration intends to require US airlines to inspect and potentially modify some fuel-tank components in 104 Boeing 747s.

The FAA suggested the requirements in a new proposed airworthiness directive that would apply to 747-SPs, 747-100s, 747-200s, 747-300s and 747-400s. It does not apply to 747-8s.

Atlas 747-400F

Source: Atlas Air Worldwide

An Atlas Air Boeing 747-400 Freighter.

The US government made the proposal public on 16 November. It marks continuation of a multi-decade FAA push, set in motion by the 1996 explosion of TWA flight 800, to prevent fuel tank fires.

The proposal follows the FAA’s receipt of “a report indicating that a certain type of fastener used in the fuel-tank walls of model 747 airplanes is insufficiently bonded to the airplane structure,” it says.

“These fasteners do not have sufficient electrical insulation applied inside the fuel tanks to prevent arcing in the event of a lightning strike or high-powered short circuit,” the proposal adds.

It calls for requiring airlines to reconfigure wire-bundle clamps, apply sealant “to certain fasteners that penetrate the fuel tank walls”, and to install “cushion clamps and polytetrafluoroethylene sleeves”.

Boeing addressed the same issue in a November 2020 service bulletin, the proposal notes.

The FAA began examining the risk of fuel-tank explosions following the in-flight explosion of TWA flight 800 in 1996. The National Transportation Safety Board attributed the event to ignition of fuel and air in the jet’s centre wing tank.

The FAA responded in May 2001, issuing a rule requiring manufacturers to “substantiate that their fuel-tank systems can prevent ignition sources in the fuel tanks”.