Japan Airlines Flight 123: Catastrophic crash after faulty repair

The history of aviation does not know another single-aircraft accident as catastrophic as this. Japan Airlines Flight 123 was supposed to be the fifth flight made by the gigantic Boeing 747 SR-46 on 12 August 1985. However, due to a faulty repair conducted seven years earlier, the aircraft crashed on a mountainside, claiming the lives of 520 people.

The Japan Airlines Boeing 747 completed its fourth flight at Haneda Airport in Tokyo shortly after 9:15 PM Greenwich Time on Monday, 12 August 1985. In less than an hour, the crew prepared the jet for takeoff, and a crew change took place.

The aircraft, led by Captain Kasami Takahama and First Officer Yutaka Sasaki, took off from Tokyo to Osaka, 450 kilometres away – at 11:12 PM Greenwich Time, the plane was already in the air. Twelve minutes after takeoff, the first signals appeared that foreshadowed the impending disaster of the jumbo jet with 524 people on board.

At 11:24 PM Greenwich Time, Captain Takahama heard a muffled boom. – "Something exploded," he said. Moments later, an alarm indicating decompression appeared in the cabin. The pilots initially suspected the landing gear doors – they assumed they had been torn off. In the next minute, the aircraft began transmitting transponder code 7700 – indicating a critical situation to controllers in Tokyo. The Japanese Boeing 747 started to lose control.

Controllers at Tokyo's Haneda Airport immediately noticed the 7700 code from Japan Airlines Flight 123 and recommended an emergency landing. In response, the pilots decided to turn the aircraft around, but the plane responded in a way they did not understand – instead of turning back, it headed in the opposite direction. During the pilots' attempts to turn, the aircraft began to rapidly descend and ascend.

Controllers in Tokyo noticed that the Japan Airlines Boeing 747 was moving chaotically. It alternated between tilting to the right and the left. It was moving in a manner characteristic of aircraft with lost stability.

– The R5 door has fallen off – said flight engineer Hiroshi Fukuda at 11:33 PM Greenwich Time. After the disaster, the team investigating the accident thoroughly analysed this statement. It determined that the mentioned door was still attached to the wreckage, so it could not have fallen off. Thus, the theory that they caused the cabin decompression was debunked. The cause of the disaster was the failure of a completely different component.

The uncontrolled flight continued for the following minutes. At 11:40 PM Greenwich Time, the jet flew near the American Yokota Air Base, whose crew intercepted communications from Flight 123. However, the Japanese in the jumbo jet did not respond to the Americans' offer of assistance, fighting at that time with losing control over Boeing.

The captain and first officer tried to control the plane using engine thrust. They discovered that pushing the power lever forward during a dive caused the aircraft to ascend. Conversely, pulling the lever back during an ascent caused the Boeing to lose speed.

In the battle to save the 524 people on board, Takahama decided to lower the landing gear, resulting in reduced speed and improved overall stability. However, this decision further degraded the already limited controllability (using engine thrust).

When the Boeing 747 approached Mount Fuji, it suddenly made a sharp right turn and began to dive. It descended at a speed exceeding 900 metres per minute, twice the recommended descent rate. The crew continuously tried to save the plane, but about 30 minutes after the first signs of trouble, the Boeing lost contact with air traffic controllers at 11:56 PM Greenwich Time. The jumbo jet crashed into the slope of Mount Osutaka at an altitude of 1,460 metres above sea level.

Experts investigating Japan Airlines Flight 123 determined that the direct cause of the accident was the rupture of the pressure bulkhead in the rear of the aircraft. Shortly after takeoff, a 2.5 square metre tear developed, causing cabin decompression. Subsequently, the airflow tore off the aircraft's vertical stabiliser, resulting in hydraulic fluid loss and loss of control, leading to the crash on the mountainside.

However, the investigators' analysis revealed that the causes of the disaster were traced back to an incident seven years before the JA123 accident. On 2 June 1978, the same jet (JA8119) struck its tail on the runway while landing at Osaka Airport. In the final phase of the manoeuvre, the pilot lifted the aircraft's nose too far, causing the rear part to strike the ground and crack the rear pressure bulkhead.

Repairs to the damaged part of the Boeing 747 were necessary. The manufacturer dispatched its specialists to perform this task. However, as the investigative committee was established seven years later (after the disaster), the repair was conducted improperly. The engineers attached the sealing element with one row of rivets, while Boeing required two rows.

Although the faulty repair allowed the Boeing 747 to complete several thousand more takeoffs and landings, the departure from Tokyo's airport on 12 August 1985 was the last that the fatiguing pressure bulkhead could endure. It cost the lives of 520 people on board. Only four injured persons survived the crash.