Improving Aircraft Safety (1980) / Chapter Skim
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B: Excerpts From Official Accident Reports
B: Excerpts From Official Accident Reports
Pages 87-100
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From page 87... ...
; and American Airlines, Inc., McDonnell-Douglas DC-10-10, N 110Ah, Chicago O'Hare International Airport, Illinois, May 25, 1979 (NTSB AAR-79-17) DAN-AIR SERVICES, LTD., BOEING 707-321 C, MAY 14, 1977 The aircraft was engaged on a nonscheduled international cargo flight, on behalf of International Aviation Services for Zambian Airlines, from London Heathrow to Lusaka International Airport, with intermediate stops at Athens and Nairobi, where there was a crew change.
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From page 88... ...
The aircraft was then cleared by Lusaka Approach to a lower altitude following behind another aircraft also bound for Lusaka International Airport. The copilot reported that the airfield was in sight.
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From page 89... ...
The rear spar center chord, and lower chord, and the front spar root attachments had failed in overload because the stabilizer had bent downwards. There was evidence of a preexisting fracture of the rear spar upper web between the top chord (adjacent to the fracture)
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From page 90... ...
why the fail-safe structure in the rear spar had failed to carry the flight loads once the top chord had fractured as a result of fatigue. In order to check the accuracy of existing stabilizer flight-load data, which had been based on wind tunnel tests and on extrapolation of flight data obtained from earlier models of the 707 aircraft, the Boeing company conducted a flight test program on a suitably instrumented 707-300 series aircraft during which horizontal stabilizer flight loads were recorded throughout the normal flight envelope.
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From page 91... ...
The original Boeing 707-300 series stabilizer differed from the 100 series design by having increased span and a redesigned rear spar of three chord construction. The rear spar was redesigned because the failsafe capability of the original structure with a top chord failure would not have been adequate to cope with the increased loads acting on the larger stabilizer.
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From page 92... ...
sortable to conclude that, because the 100 and 300 series structures It was therefore reaof the similarity of in the undamaged state, these spar chores would nave an Improved fatigue life over the original 100 series chords. The manufacturer appears to have taken this view and considered the rear spar safe in terms of fatigue in a normal service environment.
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From page 93... ...
However, the apparent lack of attention given to potential top chord failure cases outboard of the terminal fittings strongly suggests that the earlier work on the 100 series design influenced thinking on the 300 series design. While it might be considered reasonable to view the 707-100 and 300 series horizontal stabilizer structures as being broadly similar, this line of thought is only appropriate when the structures are completely undamaged.
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From page 94... ...
The replacement of the horizontal stabilizer light alloy top skin by stainless steel signif icantly altered the stiffness distribution of the structure, creating the high fastener load ings which led, ultimately, to the fatigue fail ure in the rear spar top chord in G-BEBP. Neither the inspections detailed in the approved maintenance schedule nor those recommended by the manufacturer were adequate to detect partial cracks in the horizontal stabilizer rear spar top chord, but would probably have been adequate for the detection of a completely fractured top chord.
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From page 95... ...
The National Transportation Safety Board determined that the probable cause of this accident was the asymmetrical stall and the ensuing roll of the aircraft because of the uncommanded retraction of the left-wing outboard leading edge slats and the loss of stall warning and slat disagreement indication systems resulting from the separation of the No. 1 engine and pylon assembly at
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From page 96... ...
Contributing to the cause of the accident were the vulnerability of the design of the pylon attach points to maintenance damage; the vulnerability of the design of the leading edge slat system to the damage which produced asymmetry; deficiencies in Federal Aviation Administration surveillance and reporting systems which failed to detect and prevent the use of improper maintenance procedures; deficiencies in the practices and communications among the operators, the manufacturer, and the FAA which failed to determine and disseminate the particulars regarding previous maintenance damage incidents; and the intolerance of prescribed operational procedures to this unique emergency. After the accident, the Federal Aviation Administration required a fleetwide inspection of the DC-10.
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From page 97... ...
The damaged pylon aft bulkheads of the four other American Airlines' DC-lOs were also examined at the Safety Board's metallurgical laboratory. Each of these aft bulkheads contained visible cracks and obvious downward deformations along their upper flanges.
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From page 98... ...
American Airlines engineering personnel did not perform an adequate evaluation of either the capability of the forklift to provide the required precision for the task, or the degree of difficulty involved in placing the lift properly, or the consequences of placing the lift improperly. The ECO did not emphasize the precision required to place the forklift properly.
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From page 99... ...
19. On December 19, 1978, and February 22, 1979, Continental Airlines maintenance personnel damaged aft bulkhead upper flanges in a manner similar to the damage noted on the accident aircraft.
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From page 100... ...
IMPROVING AIRCRAFT SAFETY/10 0 23. At the time of the DC-10 certification, the structural separation of an engine pylon was not considered.
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