520: The crash of Japan Airlines Flight 123 on August 12, 1985, is the single-aircraft disaster with the highest number of fatalities:[10] 520 people died on board a Boeing 747. The aircraft suffered an explosive decompression from an incorrectly repaired aft pressure bulkhead, which failed in mid-flight, destroying most of its vertical stabilizer and severing all of the hydraulic lines, making the 747 virtually uncontrollable.[11] Pilots were able to keep the plane flying for 32 minutes after the mechanical failure before crashing into a mountain. All 15 crew members and 505 of the 509 passengers on board died.[12] Japanese military personnel inaccurately assumed, during a helicopter flyover of the impact site, that there were no survivors.