In 1985, Japan Airlines Flight 123 was planned to take the sixth flight from Tokyo to Osaka at Haneda Airport. Nevertheless, the flight was cut short around twelve minutes after takeoff due to a tremor, cabin decompression, and a loud band. Following then, the plane's essential systems gradually failed, resulting in the loss of the plane and its occupants (U.S Department of Transport, n.d.).
Following the damage to the aft pressure bulkhead, the plane's cabin was decompressed. The aircraft had apparently been repaired following another mishap during landing that entailed a tail-strike event. The rapture of the bulkhead resulted in the rapid movement of air at high pressure from the cabin to the unpressurized region of the fuselage cavity which consequently destroyed the supporting structure of the vertical fin which was blown off and also the led to the failure of the APU firewall (Failure Knowledge Database, n.d.). The plane’s hydraulic components were located in the aft body and thus leading to their total damage which in turn led to a quick exhaustion of the four hydraulic systems of the airplane (U.S Department of Transport, n.d.).
Structural failure
Hydraulic and vertical fin failure
Ideally, the four hydraulic systems must be isolated, independent and separate from each other so that the failure of one of the hydraulic systems does not affect the operation of the transportation device. Similarly, the hydraulic power used for flight control is equally distributed to the four systems so that the loss of fluid in one of the systems does affect the control of the plane. However, Flight 123 had a structural disadvantage as the four systems were closely spaced due to space limitations in the aft fuselage. Also, the whole hydraulic system was located just behind the pressure bulkhead. Therefore, the accident was scheduled to happen sooner or later as the failure of the aft pressure bulkhead resulted into an overpressure that affected all the systems at one fell swoop thereby negating the redundancy that could have saved lives (Aviation Safety Network, 2017).
Mechanical failure
There were repeated cracking and fatigue cycling in the areas close to where the improper repairs were made. The repeated pressurization cycling of the bulkhead resulted in the formation of fatigue cracks along the line of fasteners that were located along the repaired zone. Unfortunately, this region was carrying the pressure loads that gradually affected its structural integrity (U.S Department of Transport, n.d.). The accident was initiated by the consistent cracking that progressed along a single row of fasteners creating a fracture line that passed through the tear straps and ending into the adjacent bays (Failure Knowledge Database, n.d.). Although the plane was designed to withstand the failure of one bay at the aft pressure bulkhead, the accident damaged the whole bulkhead. The lower part of the vertical fin was not designed to withstand very high pressures that filled the aft body thereby blowing the vertical fin from the rest of the plane (Aviation Safety Network, 2004).
Conclusion
The rupture of both the hydraulic system and the vertical tail fin made the plane impossible to control. The Captain and the pilot trainee could not conventionally control the plane in all three axes. That is the decompression led to the loss of the hydraulic fluid thereby making it impossible for the captain to control the pitch or heading through the standard flight control inputs.
References
Aviation Safety Network. (2004, October 16). CVR transcript Japan AIr Lines 123- 12 AUG 1985. Retrieved from Aviation Safety Netwrok: https://aviation-safety.net/investigation/cvr/transcripts/cvr_ja123.php
Aviation Safety Network. (2017, October 19). Accident Description. Retrieved from Aviation Safety Network: https://aviation-safety.net/database/record.php?id=19850812-1
Failure Knowledge Database. (n.d.). Case Details: Crash of Japan Airlines B-747 at Mt. Osutaka. Retrieved from Failure Knowledge database: http://www.sozogaku.com/fkd/en/cfen/CB1071008.html
U.S Department of Transport. (n.d.). Japan Airlines 747 at Gunma Prefecture. Retrieved from Federal Aviation Administration: http://lessonslearned.faa.gov/ll_main.cfm?TabID=4&LLID=16&LLTypeID=2
References
Aviation Safety Network. (2004, October 16). CVR transcript Japan AIr Lines 123- 12 AUG 1985. Retrieved from Aviation Safety Netwrok: https://aviation-safety.net/investigation/cvr/transcripts/cvr_ja123.php
Aviation Safety Network. (2017, October 19). Accident Description. Retrieved from Aviation Safety Network: https://aviation-safety.net/database/record.php?id=19850812-1
Failure Knowledge Database. (n.d.). Case Details: Crash of Japan Airlines B-747 at Mt. Osutaka. Retrieved from Failure Knowledge database: http://www.sozogaku.com/fkd/en/cfen/CB1071008.html
U.S Department of Transport. (n.d.). Japan Airlines 747 at Gunma Prefecture. Retrieved from Federal Aviation Administration: http://lessonslearned.faa.gov/ll_main.cfm?TabID=4&LLID=16&LLTypeID=2
