Philippine Airlines Flight 143

Probable cause

It is thought the vapors ignited due to damaged wiring, because no bomb, incendiary device, or detonator had been found at the scene. The airline had fitted logo lights after delivery which required passing additional wires through the vapor seals in the fuel tanks. The NTSB recommended to the FAA that an Airworthiness Directive be issued requiring inspections of the fuel boost pumps, float switch, and wiring looms because signs of chafing had been found. The FAA declined to issue the Airworthiness Directive.

The NTSB later determined the same causes had resulted in the crash of TWA Flight 800 on July 17, 1996, where all 230 passengers and crew on the Boeing 747 were killed in the accident. Ignition of the vapors within the center wing tank is also believed by the NTSB to be the cause behind the explosion of another Boeing 737 on March 3, 2001, which was operating as Thai Airways International Flight 114. Seven of the eight crew members aboard survived, the accident occurring before the boarding of passengers had taken place. The FAA did not mandate any changes to prevent center wing tank ignition aboard aircraft until July 2008, after which, the FAA required all passenger aircraft built after 1991 to implement or install preventative technology to avoid future center wing tank ignition, with a deadline set for 2010. The mandate also required all newly constructed aircraft to be fitted with the same equipment.