I too worked at Boeing, Everett, managing systems installation and fuel tank closure on all wide bodies for 40 years, 747’s at that time. I was there during investigation. Official results were that explosion was caused by spark from FQS (fuel quantity indicating system). Most of us called bs on the cause as voltage and amperage was too low. Tank is ambient atmospheric vented thru upper panel vent system as fuel is burned. Fuel is burned from center tank first to facilitate less weight on gear in event of emergency landing. All of us on team thought it was some kind of external ordinance. We made big changes to fuel tanks and eventually added nitrogen purge to displace air. It seemed a coverup to most of us, but we were only manufacturing and built the things as directed. That’s the Everett side of story.

I too worked at Boeing, Everett, managing systems installation and fuel tank closure on all wide bodies, 747’s at the time. I was there during investigation. Official results were that explosion was caused by spark from FQS (fuel quantity indicating system). Mist if us called bs on the cause as voltage and amperage was too low. Tank is ambient atmospheric vented thru upper panel vent system as fuel is burned. Fuel is burned from center tank first to facilitate less weight on gear in event of emergency landing. All of us on team thought it was some kind of external ordinance. We made big changes to fuel tanks and eventually added nitrogen purge to displace air. It seemed a coverup to most of us, but we were only manufacturing and built the things as directed. That’s the Everett side of story.