Japan Air Lines Flight 123

Investigation

Japan's Aircraft Accident Investigation Commission published their final report on the accident on June 19, 1987. The official cause of the crash according to the investigation was:

The aircraft was involved in a tailstrike incident at Osaka International Airport seven years earlier as JAL Flight 115, which damaged its aft pressure bulkhead.

The subsequent repair of the bulkhead did not conform to Boeing's approved repair methods. For reinforcing a damaged bulkhead, Boeing's repair procedure calls for one continuous splice plate with three rows of rivets. The Boeing repair technicians, however, had used two splice plates parallel to the stress crack. Cutting the plate in this manner negated the effectiveness of the row of rivets, reducing the part's resistance to fatigue cracking to about 70% of that for a correct repair. The post-repair inspection by JAL did not discover the defect, as it was covered by overlapping plates. During the investigation, the Accident Investigation Commission calculated that this incorrect installation would fail after about 11,000 pressurization cycles; the aircraft accomplished 12,318 successful flights from the time that the faulty repair was made to when the crash happened.

Consequently, after repeated pressurization cycles during normal flight, the bulkhead gradually began cracking near the row of rivets holding it together. When it finally failed, the resulting rapid decompression ruptured the lines of all four hydraulic systems and ejected the vertical stabiliser. With many of its flight controls disabled, the aircraft became uncontrollable.

In 2025, it was reported that, according to Hideji Kenjo, an officer with the Gunma Prefectural Police who worked on the case, the identification and autopsies of the victims was conducted in a gymnasium that had been converted into a morgue for the purposes of the investigation, and that the process lasted over a month from the date of the crash.