Japan Airlines Flight 123 crashed on August 12, 1985, because of an explosive decompression caused by the structural failure of a faulty repair to the plane's rear pressure bulkhead.
The primary chain of events and causes included:
• The 1978 Tailstrike: Seven years before the accident, the Boeing 747 suffered a tailstrike during a landing at Osaka International Airport, which damaged the aircraft's rear pressure bulkhead.
• Improper Repair: When Boeing technicians repaired the bulkhead, they used two separate splice/doubler plates instead of a single continuous plate with the required three rows of rivets. One plate only had a single row of rivets.
• Metal Fatigue Failure: Over thousands of subsequent pressurization and depurassurization cycles, metal fatigue weakened the improperly spliced joint until it could no longer hold the cabin pressure.
• Explosive Decompression and Loss of Control: Twelve minutes into the flight, the bulkhead ruptured, and escaping high-pressure air blew off