The deadliest single-aircraft accident

Japan Airlines Flight 123 was a Japan Airlines domestic flight from Tokyo International Airport (Haneda) to Osaka International Airport (Itami) on August 12, 1985. The Boeing 747-SR46 that made this route, registered JA8119, suffered mechanical failures 12 minutes into the flight and 32 minutes later crashed into two ridges of Mount Takamagahara in Ueno, Gunma Prefecture, 100 kilometers from Tokyo, on Monday 12 August 1985. The crash site was on Osutaka Ridge (, Osutaka-no-One), near Mount Osutaka. All 15 crew members and 505 out of 509 passengers died, resulting in a total of 520 deaths and 4 survivors.

It is currently the deadliest single-aircraft accident in history, and Japan's worst air disaster.

Sequence of events

 

The flight took off from Runway 15L at Tokyo International Airport (commonly referred to as Haneda Airport) in Ōta, Tokyo, Japan at 6:12 p.m., 12 minutes behind schedule. About 12 minutes after takeoff, as the aircraft reached cruising altitude over Sagami Bay, the rear pressure bulkhead failed. The resulting explosive decompression tore the vertical stabilizer from the aircraft and severed all four of the aircraft's hydraulic systems. A photograph taken from the ground some time later confirmed that the vertical stabilizer was missing. The loss of cabin pressure at high altitude had also caused a lack of oxygen throughout the cabin, and emergency oxygen masks for passengers soon began to fail. Flight attendants, including one who was off-duty and flying as a passenger, administered oxygen to various passengers using hand-held tanks.

The pilots, including Captain Masami Takahama first officer Yutaka Sasaki, and flight engineer Hiroshi Fukuda set their transponder to broadcast a distress signal to Tokyo Area Control Center, which directed the aircraft to descend and gave it heading vectors for an emergency landing. Continued control problems required them to first request vectors back to Haneda, then to Yokota (a U.S. military air base), then back to Haneda again as the aircraft wandered uncontrollably.

By then all hydraulic fluid had drained away through the rupture. With total loss of hydraulic control and non-functional control surfaces, the aircraft began to oscillate up and down in a phugoid cycle. The pilots managed a measure of control by using differential engine thrust. These improvisations proved helpful, but further measures to exert control, such as lowering the landing gear and flaps, interfered with control by throttle, and the plane's uncontrollability once again escalated.

After descending to 13,500 feet (4100 m), the pilots reported the aircraft's uncontrollability. The plane flew over the Izu Peninsula, headed for the Pacific Ocean, then turned back toward the shore and descended to below 7,000 feet (2100 m) before the pilots managed to return to a climb. The aircraft reached an altitude of 13,000 feet (4000 m) before entering an uncontrollable descent into the mountains and disappearing from radar at 6:56 p.m. and 6,800 feet (2100 m). The final moments of the plane occurred when it clipped one mountain ridge then hit a second one during another rapid plunge, 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 said that the area where the aircraft crashed was referred to as the "Tibet" of Gunma Prefecture.

Thirty-two minutes elapsed from the time of the bulkhead explosion to the time of the final crash, long enough for some passengers to write farewells to their families. Subsequent simulator re-enactments of the mechanical failures suffered by Flight 123 failed to produce a better solution or outcome, and in fact none of the four flight crews in the simulations were able to keep the plane aloft for as long as the 32 minutes achieved by the actual crew.

Delayed rescue operation

United States Air Force controllers at Yokota Air Force base situated near the flight path of Flight 123 had been monitoring the distressed aircraft's calls for help. They maintained contact throughout the ordeal with Japanese flight control officials and made their landing strip available to the airplane. After losing track on radar, a U.S. Air Force C-130 from the 345 TAS was asked to search for the missing plane. The C-130 crew was the first to spot the crash site 20 minutes after impact, while it was still daylight. The crew radioed Yokota Air Base to alert them and directed an USAF Huey helicopter from Yokota to the crash site. Rescue teams were assembled in preparation to lower Marines down for rescues by helicopter tow line. The offers by American forces of help to guide Japanese forces immediately to the crash site and of rescue assistance were rejected by Japanese officials. Instead, Japanese government representatives ordered the U.S. crew to keep away from the crash site and return to Yokota Air Base, stating the Japan Self-Defense Forces (JSDF) were going to handle the entire rescue alone.

Although a JSDF helicopter eventually spotted the wreck during the night, poor visibility and the difficult mountainous terrain prevented it from landing at the site. The pilot of the JSDF helicopter reported from the air that there were no signs of survivors. Based on this report, JSDF ground personnel did not set out to the actual site the night of the crash. Instead, they were dispatched to spend the night at a makeshift village erecting tents, constructing helicopter landing ramps and in other preparations, all some 63 kilometers from the wreck. JSDF did not set out for the actual crash site until the following morning. Medical staff later found a number of passengers' bodies whose injuries indicated that they had survived the crash only to die from shock or exposure overnight in the mountains while awaiting rescue. One doctor said "If the discovery had come ten hours earlier, we could have found more survivors."

Yumi Ochiai, one of the four survivors out of 524 passengers and crew, recounted from her hospital bed that she recalled bright lights and the sound of helicopter rotors shortly after she awoke amid the wreckage, and while she could hear screaming and moaning from other survivors, these sounds gradually died away during the night.

Cause

The official cause of the crash according to the report published by Japan's then Aircraft Accidents Investigation Commission is as follows:

1. The aircraft was involved in a tailstrike incident at Osaka International Airport on 2 June 1978, which damaged the aircraft's rear pressure bulkhead.
2. The subsequent repair of the bulkhead did not conform to Boeing's approved repair methods. The Boeing technicians fixing the aircraft used two separate doubler plates, one with two rows of rivets and one with only one row while their procedure calls for one continuous doubler plate with three rows of rivets to reinforce the damaged bulkhead. This reduced the part's resistance to metal fatigue by 70%. According to the FAA, the one "doubler plate" which was specified for the job (the FAA calls it a "splice plate" - essentially a patch) was cut into two pieces parallel to the stress crack it was intended to reinforce, "to make it fit". This negated the effectiveness of two of the rows of rivets. During the investigation Boeing calculated that this incorrect installation would fail after approximately 10,000 pressurizations; the aircraft accomplished 12,318 take-offs between the installation of the new plate and the final accident.
3. When the bulkhead gave way, the resulting explosive decompression ruptured the lines of all four hydraulic systems. With the aircraft's flight controls disabled, the aircraft became uncontrollable.