This is an investigative report about Japan Airline (JA8119) which was on a domestic flight from Tokyo-Haneda to Osaka. The airplane crashed into the Osutaka Ridge, on Monday August 23, 1985. All 15 crews members and 505 out of 509 passengers died, resulting in a total of 520 deaths. It remains as the deadliest single aircraft disaster in history. This report provides an engineering evaluation and recommendation about the structural failure of Japan Airliner (JA8119). The structural failure was caused by the ruptured of the rear pressure bulkhead which led to inoperative primary controls. Safety measures were then implemented by National Transportation Safety Board after incident such as modified empennage design, hydraulic fuse installed, design of model re-evaluated and inspection program revised.
Introduction
Purpose of Report
The purpose of this report is to provide an engineering evaluation and recommendation about the structural failure of Japan Airliner (JA8119).
Background Information
JA8119 was on a flight to Osaka from Tokyo-Haneda on 12 Aug 1985. However, it suffered problems a few minutes later after taking off. An hour later, the plane crashed onto the Osutaka Ridge, bursting into flames. This incident took away 520 lives out of the 524 onboard. Thus, an investigation is carried out and therefore, there is a need for this report.
Methodology
The method that was used to obtain information about this incident was through online articles (e.g. www.aviation-safety.net).
Scope
The areas of focus for this report are leading particulars and other related information on incident aircraft. Also, evaluation on failure mode of and to aircraft during incident was conducted. Lastly, the report will cover recommendation of preventive methods.
2.0 Areas and Causes of Structural Failure
2.1 Details of Plane Crash
According to Aviation Safety Network (2010), Japan Airline (JA8119) was a Japan Airline Boeing 747SR. This aircraft had a high density seating arrangement specially designed for domestic flights which can hold up to a number of 550 passengers. It had 11 years and 4 months of flying experience. On 12 August 1985, JA8119 was on an internal flight to Osaka-Itami from Tokyo-Haneda. A few minutes after the plane has taken off, an unusual vibration occurred. An impact force raised the nose of the plane and was uncontrollable. Many parts on the plane such as, R5 door, rear pressure bulkhead, vertical fin and tailcone were damaged. The primary controls also became inoperative. Therefore, controlling the plane was difficult and eventually, it struck onto the Osutaka Ridge an hour later, bursting into flames. This incident took away 520 lives out of the 524 onboard. Out of the 520, 15 of them were crews and the remaining were passengers.
Figure1: Photo taken by a witness the vertical stabilizer is missing from JA8119 [Bookrags.com 2010]
2.2 Damaged Areas
According to an online article in www.bookrags.com (2010), the areas that were damaged during the incident were R5 door, rear pressure bulkhead, vertical fin, tailcone, aileron, rudder and elevator. As stated in the article, about 12 minutes after takeoff, the rear pressure bulkhead ruptured. This caused an explosion at the rear fuselage which tore the vertical fin and tailcone. Losing the vertical fin also means that the rudder was destroyed. All four lines of hydraulic systems were severed. This also caused the aileron and elevator to be inoperative. With all the control surfaces lost, the aircraft was stuck in a phugoid cycle which began to move up and down. Phugoid cycle is a flight mode typical of accidents that disable an aircraft's controls. During the phugoid cycle, the pilots used the engine thrust to manage a small measure of control. The explosion that preceded the crash also caused the R5 door to be malfunctioned. According to a telling account of the accident by one of the survival, there was a sudden decompression in the cabin which started from the rear of the aircraft. The ceiling tiles over the rear toilets were also ripped off.
2.3 Causes of Damage
The main cause for this incident was found out to be due to rupture of the aft pressure bulkhead of the aircraft. This also caused the subsequent ruptures of the fuselage tail, vertical fin, and the four hydraulic systems. These ruptures caused the deterioration of the flying quality and the loss of primary flight control functions which led to the crash. The aft pressure bulkhead ruptured because the strength of it was already reduced greatly even before the flight. The reduced strength was caused by fatigue cracks which were extending at the joined portion of the bulkhead's webs. The bulkhead in turn became unable to sustain the cabin's pressure in flight at that time (Aviation Safety Network 2010).
2.3.1 Past Structural Damage
According to Civil Aviation Disaster (2010), the aircraft was found that it had suffered a tail strike upon touchdown on a flight to Osaka on June 2, 1978. This incident caused the rear underside of the fuselage as well as the rear pressure bulkhead to be damaged. It was then repaired by the Boeing Engineers by replacing the lower part of the rear fuselage and a portion of the pressure bulkhead. However, the reparation was flawed. As stated in the website, 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, and a gap resulted from only a single row of rivets holding the splice. It was found that this condition reduced its resistance to 70% fatigue. The fatigue cracks also had not been found in later maintenance inspection which contributes to the propagating of the cracks. Therefore, when the bulkhead gave way during the flight, it ruptured the tail assembly and severed the hydraulic systems.
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3. Conclusion
In conclusion, the tragedy of Japan Airline (JA8119) remains as the deadliest single aircraft disaster in history with a fatalities of all 15 crews and 505 passengers out of the 509 dead. This was resulted from the negligence of the Boeing Engineers during the reparation of the pressure bulkhead after the tailstrike in 1978. They were supposed to use a doubler plate with two rows of rivets to cover the damaged bulkhead, but instead they used two doubler plates with only one row of rivets. This in turn greatly reduced the strength thus, causing fatigue cracks. These fatigues cracks propagated during the flight and finally, to the extent that it was unable to endure the pressure and eventually ruptured. The rupturing of the bulkhead caused the R5 door, rear pressure bulkhead, vertical fin, tailcone, aileron, rudder and elevator to be damaged. With the loss of all primary controls, the plane could only be controlled through the engine thrust. Eventually, it struck only Osutaka Ridge. Safety measures were then taken to reduce such incident from happening in future.
4. Follow-Up/ Safety Measures
According to Aviation Safety Network (2010), the National Transportation Safety Board issued several recommendations in December 1985 after the incident. These recommendations addressed a.o. design, maintenance and inspections issues relating to the pressure bulkhead.
Firstly, the manufacturer was required to modify the design of the Boeing 747 empennage by adding a structural cover for the opening within the empennage. This is to ensure that in the event of a significant pressure that is built up in the normally unpressurized empennage, the structural integrity of the stabilizers will be protected. This modification was associated on all Boeing 747 airplanes.
Secondly, the manufacturer was required to install a hydraulic fuse in hydraulic system on all Boeing 747 series airplanes. This is to ensure that in the event of an emergency, all four hydraulic systems will not be impaired.
Thirdly, the design of the Boeing 747 and 767 aft pressure bulkhead was re-evaluated. This was done by requesting Boeing to analyze and test further the pressure bulkhead to demonstrate the validity of the fail-safe "flapping" failure mode. Fail-safe means that in the event of failure, the bulkhead responds in a way that will cause no harm, or at least minimum of harm to other parts on the aircraft.
Lastly, the inspection program for the Boeing 747 rear pressure bulkhead was revised to establish an inspection beyond the routine visual inspection performed. This is to detect the extent of any possible multiple site fatigue cracking such as nanotubes.
