An Aircraft Accident

1. Project Overview

The main objective of our project is to investigate an aircraft accident using the MEDA methodology and to understand how a series of contributing factors had caused the accident to happen. Students will also suggest ways to prevent such an accident from happening again.

1.1 Synopsis.

Japan Airlines Flight 123 was a scheduled domestic Japan Airlines passenger flight from Tokyo's Haneda Airport to Osaka International Airport, Japan. On Monday, August 12, 1985, a Boeing 747SR operating this route suffered a sudden decompression 12 minutes into the flight and crashed into two ridges of Mount Takamagahara in Ueno, Gunma Prefecture, 100 kilometers (62 miles) from Tokyo 32 minutes later. The crash site was on Osutaka Ridge, near Mount Osutaka. Casualties of the crash included all 15 crew members and 505 of the 509 passengers; some passengers survived the initial crash but subsequently died of their injuries hours later, mostly due to delays in the rescue operation. It remains the deadliest single-aircraft accident in aviation history, the second-deadliest Boeing 747 accident and the second-deadliest aviation accident after the 1977 Tenerife airport disaster.

1.2 General Information.

The accident aircraft was registered JA8119 and was a Boeing 747-146SR (Short Range). Its first flight was on January 28, 1974. It had more than 25,000 airframe hours and more than 18,800 cycles (one cycle equals one takeoff and landing). Route of JAL123The aircraft landed at Haneda from New Chitose Airport at 4:50PM as JL514. After more than an hour on the ramp, Flight 123 pushed back from gate 18 at 6:04 p.m. and took off from Runway 15L at Haneda Airport in Ōta, Tokyo, Japan, at 6:12 p.m., twelve minutes behind schedule. About 12 minutes after takeoff, at near cruising altitude over Sagami Bay, the aircraft's aft pressure bulkhead burst open due to a pre-existing defect stemming from a panel that had been incorrectly repaired after a tailstrike accident 7 years earlier. This caused a rapid decompression, with pressurized air rushing out of the cabin, bringing down the ceiling around the rear lavatories. The compressed air then burst the unpressurized fuselage aft of the bulkhead unseating the vertical stabilizer and severing all four hydraulic lines. A photograph, taken from the ground sometime later, confirmed that the vertical stabilizer was missing.

1.3 Pilot Information.

Captain Masami Takahama (高浜 雅己 Takahama Masami) from Akita, Japan, served as a training instructor for First Officer Yutaka Sasaki on the flight, supervising him while handling the radio communications. A veteran pilot, having logged approximately 12,400 total flight hours, roughly 4,850 of which were accumulated flying 747s, Masami Takahama was aged 49 at the time of the accident.

First Officer Yutaka Sasaki from Kobe flew Flight 123 as a training flight as part of his requirements to be promoted to Captain. Sasaki, who was 39 years old at the time of the incident, had approximately 4,000 total flight hours to his credit and he had logged roughly 2,650 hours in the 747.Flight Engineer Hiroshi Fukuda from Kyoto, the 46-year-old veteran flight engineer of the flight who had approximately 9,800 total flight hours, of which roughly 3,850 were accrued flying 747s.

2. Investigation Findings

2.1 Rapid decompression was caused by a faulty repair

Correct and incorrect splice plate installation to the bulkhead

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

The aircraft was involved in a tailstrike incident at Osaka International Airport seven years earlier as JAL Flight 115, which damaged the aircraft's rear pressure bulkhead.

The subsequent repair of the bulkhead did not conform to Boeing's approved repair methods. The Boeing technicians fixing the aircraft used two separate splice plates, one with two rows of rivets and one with only one row when the procedure called for one continuous splice plate (essentially a patch or doubler plate) with three rows of rivets to reinforce the damaged bulkhead. The incorrect repair reduced the part's resistance to metal fatigue to about 70% compared to the correctly executed repair. According to the Federal Aviation Administration, the one splice plate which was specified for the job was cut into two pieces parallel to the stress crack it was intended to reinforce, " to make it fit". This negated the effectiveness of one of the rows of rivets.

During the investigation, Boeing calculated that this incorrect installation would fail after approximately 10,000 pressurization cycles; the aircraft accomplished 12,318 successful flights from the time that the faulty repair was made to when the crash happened.

When the bulkhead gave way, the resulting rapid decompression ruptured the lines of all four hydraulic systems and ejected the vertical stabilizer. With the aircraft's flight controls disabled, the aircraft became uncontrollable.

Diagram of the aft pressure bulkhead This photograph shows the plane as it looked after rapid decompression. The vertical stabilizer is missing. The pilots set their transponder to broadcast a distress signal. Tokyo Area Control Center directed the aircraft to descend and follow emergency landing vectors. Because of control problems, Captain Takahama requested a vector to Haneda, declining ATC's suggestion to divert to Nagoya Airport. Hydraulic fluid completely drained away through the rupture. With total loss of hydraulic control and non-functional control surfaces, plus the lack of stabilizing influence from the vertical stabilizer, the aircraft began up and down oscillation in a phugoid cycle. In response, the pilots exerted efforts to establish stability using differential engine thrust.

Further measures to exert control, such as lowering the landing gear and flaps, interfered with control by throttle; the aircrew's ability to control the aircraft deteriorated.Upon descending to 13,500 feet (4100 m), the pilots reported an uncontrollable aircraft. Heading over the Izu Peninsula the pilots turned towards the Pacific Ocean, then back towards the shore; they descended below 7,000 feet (2100 m) before returning to a climb. The aircraft reached 13,000 feet (4000 m) before entering an uncontrollable descent into the mountains and disappearing from radar at 6:56 p.m. at 6,800 feet (2100 m). In the final moments, the wing clipped a mountain ridge. During a subsequent rapid plunge, the plane then slammed into a second ridge, 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 magazine said that the area where the aircraft crashed was referred to as the "Tibet" of Gunma Prefecture. The elapsed time from the bulkhead failure to when the plane hit the mountain was 32 minutes.

2.2 Delayed rescue operation

United States Air Force controllers at Yokota Air 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 aeroplane. The Atsugi Naval Base also cleared their runway for JAL 123 after being alerted of the ordeal. After losing track on radar, a U.S. Air Force C-130 from the 345th 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 sent the location to Japanese authorities and radioed Yokota Air Base to alert them and directed a Huey helicopter from Yokota to the crash site. Rescue teams were assembled in preparation to lower Marines down for rescues by helicopter tow line. Despite American offers of assistance in locating and recovering the crashed plane, an order arrived, saying that U.S. personnel were to stand down and announcing that the Japan Self-Defense Forces were going to take care of it themselves and outside help was not necessary. To this day, it is unclear who issued the order denying U.S. forces permission to begin search and rescue missions.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 reported from the air that there were no signs of survivors. Based on this report, JSDF personnel on the ground did not set out to the 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 engaging in other preparations, all 63 kilometers (39.1 miles) from the wreck. Rescue teams did not set out for the crash site until the following morning. Medical staff later found bodies with injuries suggesting that individuals had survived the crash only to die from shock, exposure overnight in the mountains, or from injuries that, if tended to earlier, would not have been fatal.

3. Maintenance Error

3.1 Servicing Error

Japan's Aircraft Accident Investigation Commission officially concluded that the rapid decompression was caused by a faulty repair after a tailstrike incident during a landing at Osaka Airport seven years earlier. A doubler plate on the rear bulkhead of the plane was improperly repaired, compromising the plane's airworthiness. Cabin pressurization continued to expand and contract the improperly repaired bulkhead until the day of the accident, when the faulty repair finally failed, causing the rapid decompression that ripped off a large portion of the tail and caused the loss of hydraulic controls to the entire plane.Japan's Aircraft Accident Investigation Commission officially concluded that the rapid decompression was caused by a faulty repair after a tailstrike incident during a landing at Osaka Airport seven years earlier. A doubler plate on the rear bulkhead of the plane was improperly repaired, compromising the plane's airworthiness. Cabin pressurization continued to expand and contract the improperly repaired bulkhead until the day of the accident, when the faulty repair finally failed, causing the rapid decompression that ripped off a large portion of the tail and caused the loss of hydraulic controls to the entire

4. Recommendations

As a result of this accident and several others involving operations in snow and icing conditions, the National Transportation Safety Board issued the following recommendation to the FAA on January 28, 1982:Evaluate any procedures approved to repair Boeing 747 and Boeing 767 aft pressure bulkheads to assure that the repairs do not affect the "fail-safe" concept of the bulkhead design, which is intended to limit the area of pressure relief in the event of a structural failure.Revise the inspection program for the Boeing 747 rear pressure bulkhead to establish an inspection interval wherein inspections beyond the routine visual inspection would be performed to detect the extent of possible multiple site fatigue cracking.Fatigue testing and damage tolerance testing were completed on the Boeing 747 in March and July, 1986, respectively. A reinforced aft pressure bulkhead was installed from line number 672, delivered in February 1987.Detailed inspection by high-precision eddy current, ultrasonic wave, and x-rays be accomplished at 2,000 flight-cycle intervals (freighters) or at 4,000 flight-cycle intervals for passenger airplanes.Evaluate any procedures approved to repair the aft pressure bulkhead of any airplanes which incorporate a dome-type of design to assure that the affected repair does not derogate the fail-safe concept of the bulkhead. AD 85-22-12 was issued to address this recommendation.Issue a maintenance alert bulletin to persons responsible for the engineering approval of repairs to emphasize that the approval adequately consider the possibility of influence on ultimate failure modes or other fail-safe design criteria.Require the manufacturer to modify the design of the Boeing 747 empennage and hydraulic systems so that in the event that a significant pressure buildup occurs in the normally unpressurized empennage, the structural integrity of the stabilizers.