Failure Knowledge Database / 100 Selected Cases

Crash of Japan Airlines B-747 at Mt. Osutaka
Dec. 8th, 1985, near the ridge of Mt. Osutaka, Ueno, Gunma Prefecture
KOBAYASHI, Hideo (Yokohama National University)
TERADA, Hiroyuki (Japan Aerospace Technology Foundation)(Summary)
On August 12th, 1985, JAL flight 123, a B-747 bound for Osaka Airport, went out of control 12 minutes
after t he ta ke-off fro m H aneda Tokyo I nternational Airport, as it a pproached cru ising he ight of 7,200m,
because of fatigue failure of the aft bulkhead, followed by the structural failure of the vertical fin, resulting
the crash at Mt. Osutaka, Ueno, Gunma Prefecture after 32 minutes of irregular flight. By this accident, 520
of the 524 pa ssengers an d crew on bo ard were killed, making it th e worst single aircraft acc ident in th eworld.
1. Component
Aft Pressure Bulkhead
2. Event
The aircraft had rece ived large-scale repairs at the maintenance field at H aneda in June 1 978, after it
experienced a tail hit landing at Osaka International Airport. Fatigue failure of the aft bulkhead was due to amistake during the repairs at that time. Figures 1~3 show the details of the riveted joint that was incorrectlyrepaired by the engineering staff from Boeing. The repair was not conducted in accordance to the company
procedure. The repair w as made usin g t wo separat e s plice p lates in stead of sin gle pla te. A s a result, theentire load was transmitted through the center rivet row only, and multiple site fatigue cracks initiated fromthe rivet holes of the center row soon after the repair. These cracks propagated by the cyclic pressurizationof the aircraft and finally caused the unstable fracture of the whole structure after a total of 12,319 cycl es.
The repair mistake extended across two bays, which is about one-meter in length. As this was l onger thanthe crit ical length ne cessary for th e unstable fa ilure of t he str ucture, the crack propagat ed by theinterlinking of adjacent small cracks without being arrested.
As is sh own in Fig. 3, as a result of the mistake in the repair, the entire membrane stress in duced byinternal pressure was tra nsmitted through just the center row faste ner. Therefore, it can be judged that thefundamental mechanism of load transmission was not understood at all by the maintenance engineers.
The following issues are also pointed out.
The final check of t he repair work made by the A irline representatives and air tr ansportation authority
was insufficient. Even though the site of the repair mistake was covered with sealant, the check should havebeen able to identify the problem.
The issue of periodical maintenance and inspection over the course of the 12,319 flights conducted after
the repair was also problematic, since the inspection was not conducted before accident.
1Failure Knowledge Database / 100 Selected Cases

3. Course
Many structural parts of the vertical fin were retrieved from Suruga Bay, where the first decompression
occurred. The most of t he wreckage was found at the site of crash. The wreckage of t he aft fuselage wasreconstructed at the Chofu Airfield, and the initial investigation focused mainly on the cause of the fractureof the aft pressure bulkhead.
4. Cause
The direct c ause of th e a ccident w as t he fati gue fai lure of t he aft bulkhead as s hown in Fig. 1. T hecentral hydra ulic c ontrolling system and APU loc ated at t he ba ck of b ulkhead a s w ell as the box-beam
structure of the vertical fin were blown off by the large mass of air moving a hypersonic velocity that wasinduced by this breakage.
As a result of the total loss of hy draulic pressure, the aircraft w ent out of co ntrol and fi nally crashednear the ridge of Mt. Osutaka, although it was able to stay in the air for 32 minutes and avoid an immediate
mid-air explosion.
5. Immediate Action
Among other investigations, the aft pressure bulkhead where the large-scale repairs had been conducted
after the tail hit a ccident a t Osaka air port seven years ago were cl osely exam ined. Deta iled fract graphyobservations of the fracture surface of the fastener joint were made.
6. Countermeasure
Even though the main cause of the ac cident was the mistake during the repair of the pressure bulkhead
conducted seven years befo re the accident, the direct cause that led the aircraft losing control was the lossof the hydraulic control unit and the vertical fin. The Aircraft Accident Investigation Commission advised
the manufacturer and opera tor to re inforce the torsi on bo x structure by inst alling a plat e t o prevent t hehigh-speed airflow fro m ent ering t he box beam in t he event th at the pressure bu lkhead do es burst. The
advice was put into practice.
7. Knowledge(1) Inspections conducted at appropriate intervals are indispensable, especially after a large-scale repair ordesign c hange has been c arried out in order t o e nsure tha t t he d esigner's intent ion is c ompletely
satisfied.
(2) Fundamental training and education in areas such as the mechanics of materials should be provided indetail even for the engineers at the site.
(3) The people who are responsible for signing the document of approval of repairs should check the site
carefully to assure that those repairs were conducted as desired.
8. BackgroundThe syste m for ensuring the structur al int egrity a fter a l arge-scale rep air wa s in adequate. At JAL, th e2Failure Knowledge Database / 100 Selected Cases

concept of m aking freq uent i nspections that is esse ntial for e nsuring th e integrity of th e s tructures,
especially when a large-scale repair was conducted as the present case, did not exist.
9. Sequel
The fast and unstable fracture of the pressure b ulkhead of the jumbo jet aircraft was the result of t hepropagation and linking up of multiple site cracks that emanated from the riv et holes. Figure 6 s hows thebehaviors of t hese cracks at the location L18 of the fas tener joint. Because of the mistake in the repair of
the b ulkhead, t he lo ad was tra nsmitted t hrough t he ce nter row fas tener only. Because t he stres s be came
highly co ncentrated ther e, m ultiple-site cracks started fro m many of th e fas tener holes, and those cra cks
linked-up to became long enough after 12,300 pressurization cy cles to c ause the fracture . In fac t, it wasreported that fatigue cracks were observed at more than 30 of the 50 fastener holes in the repaired area, andtotal length of the cracks was more than 270 mm. These damages led to the fatigue failure of the bulkheadin the last flight.
One reason why multiple-site cracks occurred is that the old rivet holes were used again at the repair
without resizing the holes. The JAL accident showed the potential danger of multiple-site cracks.
Three years later, on April 4th, 1988, another accident caused by multi-site damage occurred in Hawaii.
This time a la rge part of the fuselage structure of a B-737 operated by Aloha Airlines w as blown off
while cru ising. These two accident c ases that we re ca used by m ultiple-site d amage (M SD) a nd
multiple-element damage (MED) showed that the damage tolerant design concept based on the behavior ofa single crack is insufficient for such cases.
Since the accident of Comet-I, disasters caused by fatigue failure was repeated after 31 years. The causeof the Comet accident was a design problem that was common to the entire fleet, while in the case of theJAL accident the problem was in the repair and therefore was an individual matter. By tracing the history offatigue related accidents, one can suggest the direction of future research on this subject.
10. On the Side
In 1989, a similar accident occurred in the USA. A DC-10 operated by United Airlines lost control whenthe entire hydraulic system was totally damaged because of th e failure of th e compressor fan d isk of t hefirst stage in the second engine located at the em pennage. However, in contrast to the JAL case where thecockpit crew did not recognize the severity of the situation and insisted on returning to the original airport,
the crew of DC-10 correc tly un derstood th at t he e ngine co ntrolling t he hy draulic un it w as fractured .
Therefore they tried t o land at th e nearest airstrip as s oon as possible. Although they were forced to m ake
crash landing an d a fire broke o ut s oon after the t ouch down, m ore th an 6 0% of th e people on- board
survived.
If the pilot is ab le to corre ctly assess what is occurring on t he aircraft a nd oper ate according to t hat
assessment, the worst results can always be avoided. In the case of the JAL accident, the pilot thought thathe c ould ret urn safely bec ause h e t hought t hat only t he rear car go door (R 5 D oor) w as fractured, eventhough t here had been t ime to understand t he fa cts of the s ituation correc tly w ith the s upport of o ther
aircraft, as the aircraft was able to stay in the air for 32 minutes.
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Failure Knowledge Database / 100 Selected Cases

11. Social Impact
As the accident involved a Jumbo Jet that is used all over the world, much concern was raised just after
the tragedy as to whether or not the accident cause was common to the fleet.
The accident was long talked about as a tragedy, because so many people were killed. JAL, the biggest
airline in Japan, lost much of its cred ibility, and it took long time to regain consumer trust in the company
and restore the number of air travelers in Japan.
12. Information Source(1) Aircraft Accident In vestigation R eport 62-2 (1 987), Aircraft A ccident Inv estigation C ommission,
Ministry of Transportation of Japan.
(2) H. Kobayashi, Safety Engineering, 26-338 (1987).
13. Primary Scenario
01. Ignorance
02. Insufficient Knowledge
03. Lack of Learning
04. Carelessness
05. Insufficient Precaution
06. Carelessness of Worker
07. Misjudgment
08. Misperception
0 9. Misapprehension/Misread
10. Ignorance of Procedure
11. Insufficient Communication
12. Lack of Confirmation
13. Usage
14. Maintenance/Repair
15. Change of Components
16. Pressure Bulkhead
17. Usage
18. Maintenance/Repair
19. Poor Inspection
20. Failure
21. Fracture/Damage
22. Fatigue
23. Unstable Fracture of Bulkhead
24. Failure
25. Fracture/Damage

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Failure Knowledge Database / 100 Selected Cases

26. Fracture of Vertical Fin
27. Non-Regular Action
28. Emergency Action
29. Stricture of Judgment
30. Malfunction
31. Poor Hardware
32. Malfunction of Control System
33. Failure
34. Large-Scale Damage
35. Crashes
36. Damage to Society
37. Change in Perception
38. Distrust to Enterprise and Authority
39. Decrease in Customers

5Failure Knowledge Database / 100 Selected Cases

Torsion strength of box beam
become zero as all panels fastenedby single row river were torn-offby hyper airflow②③

Vertical finRudder

Hypersonic airflow①

Sequence of fracture①→②→③②①
Hydraulic pipe

Auxiliary Power unit
Central hydraulic unit
R5 doorFig. 1

Aft Pressure Bulkhead
Structure near the Empennage.

6Failure Knowledge Database / 100 Selected Cases

Pressure Bulkhead

Mis-repair

False Inspection

Malfunction

Fatigue Failure

Structural Failur Induced

Results

Inspection/Repair

Yes

Yes

Yes

Loss of Control

No

Forced Landing

Yes

NoYes
No

Re-repair

NoIntegrity

NoFig. 2

Periodical Maintenance

Event Tree Analysis of JAL Accident Caused by Miss-repair of AFT Pressure.

7Failure Knowledge Database / 100 Selected Cases

Pressure Bulkhead Burst

Aircraft Response
Irregular

Aircraft Response
NormalPeriodical Inspection
Yes

Periodical Inspection
NoPeriodical Inspection
Error Inspection

Transfer Inspection
Error

Transfer Inspection
Correct

Transfer Inspection
Not inspected

Miss-Repair

False Design Repair

Other

OtherTransfer

Bottom Hit Landing

Fig. 3

Fault Tree Analysis of JAL Accident Caused by Miss-repair of Aft Pressure.

8Failure Knowledge Database / 100 Selected Cases

L12
Stiffener
WebL14

L16Upper

L18

Bay5Bay1Bay2Bay3Bay4Double row fastener Single row fastenerDouble row fastener

Lower
L20

Collector Ring
Part of aft pressure bulkhead seen from TailsideWebL22

Upper bulkhead
Force Flow

Force Flow
Splice plate

Rivet
L18 Stiffener

Miss-repaired
Hatched part should besingle plate
Fracture site

Sealant

Force concentrated
at this row

Sealant

Splice plate
Lower Bulkhead(outside)(cabin side)
Directed Repair

Actual Repair
Fig. 4The Aspect of Aft Bulkhead Repair.
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