Operating flight 123 on the afternoon of August 12, 985 was one of Japan Air Lines special short-range (SR) Boeing 747s. Modified to hold up to 550 passengers, the aircraft is structurally reinforced, and perfect for Japan's high density domestic flights. The flight came on the eve of a Japanese holiday where families traditionally return to their place of birth and the flight was filled nearly to capacity, with 509 passengers on board. Twelve flight attendants and the three flight crew brought the total to 524. Flight 123 lifted off from Tokyo's Haneda airport just after 6:00pm bound for Osaka, some 215 miles away.

Thirteen minutes later, the aircraft had reached it's cruising altitude of FL240 and was just off the coast southeast of Mt. Fuji. Suddenly, the controller handling 123 saw the aircraft's transponder code switch to 7700, the emergency setting. 123 then came on the radio, saying "Tokyo...JL123. Request immediate...ah...trouble. Request return back to Haneda...descend and maintain FL220." The controller approved the request and gave 123 a vector back towards Haneda.

The aircraft, however, seemed to be wandering and the controller again called 123 and gave it further heading instructions. Clearly the crew was under stress, so the controller told 123 that any further contact should be in Japanese to ease any further difficulties. The aircraft had now turned back inland, northbound towards Mt. Fuji. By this time, the news had gotten to JAL's headquarters back in Tokyo and the company called 123 on the company frequency.123 told them that "Ah...the R5[cabin] door is broken. Ah...we are descending now." This didn't really give any indication of the problems that 123 was having, so the company gave no further advice.

Meanwhile, the aircraft was now heading east and was down to 13,500ft. The crew called Tokyo control again at this point, saying "JL123, JL123 uncontrollable!" The controller told 123 to maintain it's heading of about 090 degrees towards Haneda, but the aircraft began a left turn, rolling out on a heading of about 340 and down to 6800ft, lower than many of the mountains in the area. As the controllers continued to talk to 123, the aircraft slowly recovered to 13,000ft. 123 asked for it's position, which was now some 45 miles northwest of Haneda. The aircraft then turned right, again nearly eastward and began a rapid descent down to 8,400ft when the aircraft's target disappeared from radar. 123 bounced off a ridge and impacted near the summit of Mt. Osutaka. Because of the rainy weather and the darkness, rescue crews were not able to reach the sight until the next morning. Incredibly, four passengers survived

......The obvious question was what catastrophic event rendered flight 123 uncontrollable. The only clue was in the transmission "Ah...the R5 door is broken." Surely though a malfunction of a cabin door wouldn't cause the difficulties that 123 experienced. Further, examination of the wreckage showed that the door was in fact closed and latched properly at the time of the accident. The aircraft involved in the accident, JA8119, was not a new aircraft and had seen a great deal of work in it's eleven years.

Even so, there had never been a fatigue-induced structural failure in the history of the 747. Terrorism was also a possibility, but two phone calls from separate terrorist groups indicated that it was not a likely explanation. The first and most dramatic clue came in the form of a photograph taken by a photographer in a mountain village. From the photo, it appeared that the aircraft was missing a large portion of it's vertical fin and tailcone. Substantiating this theory, a Japanese destroyer came across a 15-foot section of the vertical fin floating in Sagami Bay, near the same area where the Tokyo controller first saw the aircraft's transponder code switch to 7700.

Further search of the bay turned up several other pieces of the aircraft's tail assembly. Examination showed that the pieces had been substantially damaged before separating from the aircraft. One of the surviving passengers was an off duty flight attendant who was able to provide an telling account of the accident. She recalled a sudden decompression in the cabin starting in the rear of the aircraft. Ceiling tiles were ripped off over the rear toilets and the aircraft began oscillating in both the pitch and roll axes. She also recalled then engine power varying widely in response to the pitch oscillations.

On-site investigation was hampered by Japanese officials and by the time investigators were able to reach the site, critical pieces of wreckage had been moved by rescue crews. Recovery of the FDR and CVR showed that shortly after the decompression, total hydraulic failure struck the aircraft. With all three flight control surfaces disabled and the aircraft unstable due to the stabilizer loss, the crew only had the engine power to control the aircraft. Knowing that the aircraft had lost much of it's vertical fin, investigators put forth the idea that the rear pressure bulkhead may have ruptured, blowing off the tail assembly and severing the hydraulic lines.

No history of incidents of this type had been recorded and, though not by any means new, JA8119 had less than half of the total hours of the oldest 747. In fact, the pressure bulkhead had been factory tested a simulated service life of 20 years, far more than any 747 had flown and examination of the wreckage showed no signs of corrosion. Further examination of the rear bulkhead, however, provided investigators with a startling explanation of the accident. An area of the bulkhead was found to be spliced with a row of rivets. In looking at the maintenance records of the aircraft, it was found that it had suffered a tail strike on takeoff seven years prior, cracking the rear bulkhead.

Boeing's repair protocol for such damage calls for a doubler plate to be placed over the area to be spliced and a double row of rivets put in to hold it. The wreckage showed that two doubler plates had been used, the gap between resulting in only a single row of rivets holding the splice. It was found that this condition reduced it's resistance to fatigue some 70%.