About 12 minutes after takeoff, at near cruising altitude over Sagami Bay, the aircraft's aft pressure bulkhead tore open due to a preexisting defect, stemming from a panel that had been incorrectly repaired after a tailstrike accident years earlier. This caused an explosive decompression, causing pressurized air to rush out of the cabin and bring down the ceiling around the rear lavatories. The air then blew the vertical stabilizer off the aircraft, severing all four hydraulic lines. A photograph taken from the ground some time later confirmed that the vertical stabilizer was missing. Loss of cabin pressure at high altitude caused a lack of oxygen throughout; emergency oxygen masks for passengers were deployed. Flight attendants, including one off-duty, administered oxygen to various passengers using hand-held tanks.
The pilots set their transponder to broadcast a distress signal. Tokyo Area Control Center directed the aircraft to descend and follow emergency landing vectors. Because of control problems, Capt. Takahama requested a vector to Haneda, opposing ATC's suggestion to divert to Nagoya Airfield, knowing it was ideally suited for a 747 in case of an emergency.
Hydraulic fluid completely drained away through the rupture. With total loss of hydraulic control and non-functional control surfaces, plus the lack of stabilizing influence from the vertical stabilizer, the aircraft began up and down oscillation in a phugoid cycle. In response, the pilots exerted efforts to establish stability using differential engine thrust. Further measures to exert control, such as lowering the landing gear and flaps, interfered with control by throttle; the aircrew's ability to control the aircraft deteriorated.
Upon descending to 13,500 feet (4100 m), the pilots reported an uncontrollable aircraft. Heading over the Izu Peninsula the pilots turned towards the Pacific Ocean, then back towards the shore; they descended below 7,000 feet (2100 m) before returning to a climb. The aircraft reached 13,000 feet (4000 m) before entering an uncontrollable descent into the mountains and disappearing from radar at 6:56 p.m. at 6,800 feet (2100 m). In the final moments, the wing clipped a mountain ridge. During a subsequent rapid plunge, the plane then slammed into a second ridge, then flipped and landed on its back. The aircraft's crash point, at an elevation of 1,565 metres (5,135 ft), is located in Sector 76, State Forest, 3577 Aza Hontani, Ouaza Narahara, Ueno Village, Tano District, Gunma Prefecture. The east-west ridge is about 2.5 kilometres (8,200 ft) north north west of Mount Mikuni. Ed Magnuson of Time magazine said that the area where the aircraft crashed was referred to as the "Tibet" of Gunma Prefecture.
The elapsed time from the bulkhead explosion to when the plane hit the mountain was estimated at 32 minutes long enough for some passengers to write farewells to their families. Subsequent simulator re-enactments with the mechanical failures suffered by the crashed plane failed to produce a better solution, or outcome; despite best efforts, none of the four flight crews in the simulations kept the plane aloft for as long as the 32 minutes achieved by the actual crew.
was a scheduled domestic Japan Airlines passenger flight from Haneda Airport (Tokyo International Airport) to Osaka International Airport, Japan. On Monday, August 12, 1985, a Boeing 747SR operating this route suffered explosive decompression 12 minutes into the flight and, 32 minutes later, crashed into two ridges of Mount Takamagahara in Ueno, Gunma Prefecture, 100 kilometres (62 miles) from Tokyo. The crash site was on Osutaka Ridge (御巣鷹の尾根
