JAPAN AIRLINES FLIGHT 123
On August 12, 1985, Japan Airlines Flight 123 crashed in the area of Mount Takamagahara, Japan. Of the 524 people on board, 520 were killed, and it is the deadliest single-aircraft accident in aviation history.
The Flight 123 was a scheduled domestic passenger flight from Tokyo's Haneda Airport to Osaka International Airport, Japan. The captain was Masami Takahama, a veteran pilot, having logged approximately 12 400 total flight hours. The first officer was Yutaka Sasaki, who had approximately 4 000 total flight hours to his credit. Sasaki was in line for promotion to the rank of captain, and flew Flight 123 as one of his training flights. Captain Takahama served as a training instructor for Sasaki on the flight, supervising him, while handling the radio communications. The flight engineer was Hiroshi Fukuda, who had approximately 9 800 total flight hours. Both pilots and the flight engineer were killed in the accident. The accident aircraft was a Boeing 747SR-46, registered as JA8119. The Boeing 747SR is a short range variant of the Boeing 747-100, which was specifically configured for domestic flights with a high density seating arrangement.
About 12 minutes after takeoff, at near cruising altitude over Sagami Bay, an unusual vibration occurred. An impact force raised the nose of the aircraft, and control problems were experienced. The rear pressure bulkhead had ruptured, causing serious damage to the rear of the plane. This caused a rapid decompression of the aircraft, bringing down the ceiling around the rear lavatories, damaging the unpressurized fuselage rear of the bulkhead, unseating the vertical stabilizer, and severing all four hydraulic lines. Due to the damage, the hydraulic pressure dropped, and ailerons, elevators and yaw damper became inoperative. Controlling the plane was very difficult. The aircraft started to descend, while the crew tried to control the aircraft by using engine thrust. The pilots set their transponder to broadcast a distress signal. Afterwards, captain Takahama contacted Tokyo Area Control Center to declare an emergency, and to request to return to Haneda Airport, descending and following emergency landing vectors to Oshima. Tokyo Control approved a right-hand turn to a heading of east back towards Oshima, but the plane did not follow the directions, and continued to fly a westerly course. It was at this point that the pilots became aware, that the aircraft had become uncontrollable, and the flight engineer reported that the hydraulic pressure was dropping. Heading over the Izu Peninsula, the pilots managed to turn towards the Pacific Ocean, then back towards the shore. Hydraulic fluid completely drained away through the rupture. With total loss of hydraulic control and non-functional control surfaces, the aircraft began up and down oscillations in phugoid cycles, lasting about 90 seconds each. The lack of stabilizing influence from the vertical stabilizer and the rudder removed the only means to dampen yaw. Consequently, the aircraft also began to exhibit Dutch roll, simultaneously yawing right and banking right, before yawing back left and banking left. In response, the pilots exerted efforts to establish stability using differential engine thrust, and they managed to slowly turn the plane back towards Haneda. The landing gear was lowered in an attempt to dampen the phugoid cycles and Dutch rolls. This was somewhat successful, as the phugoid cycles were dampened, but lowering the gear also decreased the directional control the pilots were getting by applying power to one side of the aircraft, and the aircrew's ability to control the aircraft deteriorated. Shortly after lowering the gear, the plane began a right-hand descending turn from 22 400 feet (6 800 m) to 17 000 feet (5 200 m), then continued north while still descending. Upon descending to 13 500 feet (4 100 m) , the pilots again reported an uncontrollable aircraft. Moments later, the aircraft began to turn to the left, despite efforts by the crew to get the plane to continue to turn right and avoid the mountains.
Due to the lowered air speed caused by the drag of the undercarriage, the first officer quickly discussed lowering the flaps. The captain expressed, that without hydraulics, this wouldn't work, but the flight engineer pointed out this could be done via an alternate electrical system. The captain lowered the flaps to 5 units as an additional attempt to exert control over the stricken jet. Then the flaps were lowered to 10 units, but this began to cause the plane to bank increasingly to the right. One minute later, the flaps were extended to 25 units, which caused the aircraft to bank further to the right, and the nose began to drop. Captain Takahama immediately ordered the flaps to be extended to maximum units, and was heard on the cockpit voice recorder desperately requesting for more power to be applied, in a last-ditch effort to raise the nose. The aircraft continued to enter an uncontrollable right-hand descent into the mountains. In the final moments, the planes fourth engine clipped a ridge of a mountain, and then the plane flipped on its back, and crashed and exploded on another ridge near Mount Takamagahara.
Japan's Aircraft Accident Investigation Commission officially concluded, that the rapid decompression was caused by a faulty repair by Boeing technicians, after a tailstrike incident during a landing at Osaka Airport on June 2, 1978, which damaged the aircraft's rear pressure bulkhead. A doubler plate on the rear bulkhead of the plane, had been improperly repaired, compromising the plane's airworthiness. 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. However, the Boeing technicians carrying out the repair, had used two splice plates parallel to the stress crack. Cutting the plate in this manner, negated the effectiveness of one of the rows of rivets, reducing the part's resistance to fatigue cracking to about 70 % of that for a correct repair. Consequently, after repeated pressurization cycles during normal flight, the bulkhead gradually started to crack near one of the two rows of rivets holding it together. When it finally failed, the resulting rapid decompression ripped off a large portion of the tail, ruptured the lines of all four hydraulic systems, and ejected the vertical stabilizer. When the hydraulic controls to the entire aircraft were lost, many of the aircraft's flight controls disabled, and the aircraft became uncontrollable.
NOTABLE AVIATION ACCIDENTS AND INCIDENTS