No where near 1200 feet. There is no energy from anywhere to account for it. . . and the NTSB to this day refuses to provide their calculations about where that energy came from, and to explain how it could climb. It certainly could not climb without engines. Boeing disavowed both scenarios by saying the maximum climb rate for the 747-100 was 3800 feet per minute under ideal conditions and lift with the engines at 100%. Yet the CIA claimed that occurred in 18 seconds (which the math claims it would have to use ALL forward momentum at a maximum 9.7 Gs to achieve, which it obviously did not) and the NTSB claimed 1200 feet in 18 seconds (only 2.7 Gs but requires working engines which were NOT present) as that is within the working parameters of the aircraft were it complete. I think only in Hollywood could that airframe do that, especially with a mortally wounded Center Wing Tank as the cause of the unique explosion that blew off the nose, a Center Wing Tank that is also a Five Spar Box Girder than holds both wings to the fuselage.
Boeing disavowed both scenarios by saying the maximum climb rate for the 747-100 was 3800 feet per minute under ideal conditions and lift with the engines at 100%.
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That’s for a continuous climb. The TWA800 rear section climbed briefly and ended with a stall and ballistic descent, an entirely different scenario.