..the plane fluttered towards the ground like an autumn leaf for 30 minutes before crashing into Mount Osutaka. Amazingly, there were four survivors.
August 12, 1985: Japan Airlines Flight 123. Boeing 747-SR46, registration JA8119. One of Japan Air's specially modified 747s, with 509 passengers, 12 flight attendents, and 3 crew members aboard, suffered an aft pressure bulkhead failure at 24,000 feet. Kyu Sakamoto, best known for his song "Sukiyaki," was killed in the accident. In command of this flight was Captain Masami Takahama, 49, who had been with the company for nineteen years, and had 12,500 hours of flight time.
At 520 fatalities, it was the worst single-aircraft air disaster in history. The Boeing engineer who had approved an improper repair of the bulkhead in 1978 committed suicide after the accident.
Tragically, and somewhat ironically, the flight came on the eve of Obon, the period when Japanese traditionally return to their place of birth and visit the graves of their ancestors. The flight was filled nearly to capacity. It took off from Tokyo's Haneda airport at 6:04 p.m. bound for Osaka, roughly 215 miles away. Thirteen minutes after takeoff the aircraft reached its cruising altitude.
As the Tokyo ATC was tracking the flight, the emergency transponder code 7700 appeared on their screens. This is the emergency squawk for aircraft in distress. Suddenly the crew of 123 came on the radio, saying "Tokyo...JL123. Request immediate...ah...trouble. Request return back to Haneda...descend and maintain FL220." The air traffic controller approved, and gave heading back to Haneda. The aircraft, however, seemed to be wandering and the controller again called 123 and gave it further heading instructions. News reached JAL's corporate offices in Tokyo and the company called 123 on the company frequency. 123 told them "Ah...the R5 (cabin) door is broken. Ah...we are descending now." As this gave no indication of the problems 123 was having, the company officials gave no advice.
JAL 123 had dropped in altitude to 13,500 feet. The crew called Tokyo control again at this point, saying "JL123, JL123 uncontrollable!" Crossing the Izu Peninsula and leaving it astern, it then headed out over Suruga Bay in a north-westerly direction. The aircraft began to turn left, heading down to 6800 feet, which was lower than many of the mountains in the area, then recovered to 13,000 feet. The plane veered again, this time to the right, and began a rapid descent down to 8,400 feet, and disappeared from radar. JAL 123 glanced off a ridge and impacted near the summit of Mt. Osutaka. Rescue crews could not reach the site until the next morning due to rain and darkness.
In the wreckage, searchers found letters to families, last wills, and poetry, composed by passengers contemplating their ultimate fate while floating around in the sky for those eternal minutes.
Transcripts from the flight recorders were no help in determining the cause of the accident, and terrorism was quickly ruled out when two groups tried to claim responsibility. JA8119 was an older plane, but had only half as many hours logged as the oldest 747, and regardless, there had never been a fatigue-induced structural failure in the history of the 747. A photo taken from a mountain village showed that the aircraft was missing a large portion of its vertical fin and tailcone, and a ship came across a section of the vertical fin floating in Sagami Bay. Further searches of the bay turned up several other pieces of the aircraft's tail.
Investigators came up with the idea that the rear pressure bulkhead may have ruptured, blowing off the tail assembly. No history of incidents of this type had been recorded and in fact, the pressure bulkhead had been factory tested a simulated service life of 20 years, far more than any 747 had flown. But in looking at the maintenance records of the aircraft, it was found that it had suffered tail damage on takeoff seven years prior, cracking the rear bulkhead. Boeing's 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.
Sources:
http://www.planesafe.org
http://aviation-safety.net
http://www.aviationcrashes.com
http://www.airsafetyonline.com
http://www.jal.co.jp