Date: August 12, 1985
Place: near the ridge of Mt. Osutaka, Ueno, Gunma Prefecture
Location: JAL flight 123, a B-747
Overview: On August 12th, 1985, JAL flight 123, a B-747 bound for Osaka Airport, went out of control 12 minutes after the take-off from Haneda Tokyo International Airport, as it approached cruising height of 7,200m, because of fatigue failure of the aft bulkhead, followed by the structural failure of the vertical fin, resulting the crash at Mt. Osutaka, Ueno, Gunma Prefecture after 32 minutes of irregular flight. By this accident, 520 of the 524 passengers and crew on board were killed, making it the worst single aircraft accident in the world.
Incident: The aircraft had received large-scale repairs at the maintenance field at Haneda in June 1978, after it experienced a tail hit landing at Osaka International Airport. Fatigue failure of the aft bulkhead was due to a mistake during the repairs at that time. Figures 1~3 show the details of the riveted joint that was incorrectly repaired by the engineering staff from Boeing. The repair was not conducted in accordance to the company procedure. The repair was made using two separate splice plates instead of single plate. As a result, the entire load was transmitted through the center rivet row only, and multiple site fatigue cracks initiated from the rivet holes of the center row soon after the repair. These cracks propagated by the cyclic pressurization of the aircraft and finally caused the unstable fracture of the whole structure after a total of 12,319 cycles. The repair mistake extended across two bays, which is about one-meter in length. As this was longer than the critical length necessary for the unstable failure of the structure, the crack propagated by the interlinking of adjacent small cracks without being arrested.
