What happened
On August 12, 1985, a Boeing 747SR, registration JA8119, was operating a domestic flight from Tokyo-Haneda to Osaka. Shortly after departing at 18:12, while the aircraft was climbing through 23,900 feet at 300 knots, the crew experienced intense vibrations and a sudden upward force on the nose. A rapid decompression occurred following the rupture of the rear pressure bulkhead. This structural failure caused significant damage to the tail section, including the loss of a portion of the vertical fin and the tail cone containing the auxiliary power unit.
The resulting damage led to a drop in hydraulic pressure, rendering the ailerons, elevators, and yaw damper inoperative. The crew struggled to maintain control as the aircraft entered dangerous oscillations, specifically phugoid and dutch roll motions. Despite attempts to manage the descent using engine thrust, the aircraft's airspeed dropped significantly. After reaching an altitude of approximately 13,400 feet, the plane began a final descent. At 18:56, the aircraft struck the Osutaka Ridge, leading to a massive fire. The accident resulted in 520 fatalities and only four survivors.
Findings
Investigations determined that the primary cause of the structural failure was the rupture of the aft pressure bulkhead. This rupture was driven by fatigue cracks that had developed at the spliced portion of the bulkhead's webs. The investigation traced the origin of these cracks back to an improper repair performed on the aircraft in 1978, following a previous landing incident involving the same tail section. These cracks weakened the bulkhead's ability to withstand cabin pressure and were not detected during subsequent maintenance inspections.