. For the flight time to Beijing, the center tank would most likely have been empty except for residual fuel as a matter of 777 procedure. The main wing tanks would have sufficient fuel for the trip. Could a short that caused a spark within a fuel boost pump have ignited the trapped vapor within the center tank?
The National Transportation Safety Board attributes the explosion of TWA Flight 800 off Long Island in 1996 to this cause. That accident involved a 747 and not a 777. Boeing recommended both a mechanical and procedural modification for the potential, but not totally verified, problem for many Boeing airplanes. Airlines began the modifications within two years after the investigation was complete. Did Malaysia Airlines comply with the modification?
From an article.