8:31:11 Intact and climbing 747 approaches 13,800 feet.
8:31:12 Initiating Event at 13,800 feet followed immediately by the commencement of the decapitation process.
8:31:43-8:31:47 Streak of light appears.
8:31:47 Explosion of Massive Fireball at 5500-7500 feet.
8:31:55-8:31:57 Splashdown of the Massive Fireball flames.
Source.
Additional confirmation of the low altitude of the Massive Fireball explosion is in the following Airborne Witness Matrix of NTSB Exhibit 4-A.
Also, witnesses Sven Faret and Ken Wendell clearly stated in their own personally prepared detailed report that the Massive Fireball explosion took place below their own flight altitude of 8500 feet and that they flew over to the smoke cloud it left and found that its top was at 7700 feet.
Additionally, New York Air National Guard Major Fred Meyer also clearly indicated in his own detailed report that the elapsed time between the first explosions he saw - which looked to him like "ordnance" - and the Massive Fireball explosion was only 3-4 seconds, leaving no room for doubt that all the explosions were in close proximity to each other. He further stated in his report that he and his helicopter crewmates all agreed that the falltime of the Massive Fireball flames to the surface was approximnately 10 seconds, an obvious impossibility if the Massive Fireball explosion had taken place anywhere near 13,800 feet as the "shootdown" conspiracy theorists erroneously assumed.
Note that the "ordnance" explosions were engulfed by the Massive Fireball explosion as further documented in graphic #5 of the following sequential graphics prepared by the New York Air National Guard after debriefing Major Meyer and his Jolly 14 helicopter crewmates.
The streak of light didn't even appear until 30+ seconds AFTER the Initiating Event at 13,800 feet by which time all of the wreckage was obviously descending. Keeping in mind that the streak of light was the first fiery event seen by anybody, it's accordingly self evident that the source of all of the fiery events observed by the witnesses was burning jet fuel and that their observations were, as the NTSB contends, of the 747's final stages of crippled flight, not a missile shootdown.
Additionlly, there was no physical evidence of a missile(s) attack - or bomb - either according to ten expert metallurgists, four from NTSB, three from Boeing, two from FBI Laboratory, and one scientist consultant. Source.