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Aviation History
1982
1982 - 0236.PDF
Mechanic error? by J. M. RAMSDEN WHEN we talk about human factors in flight safety, we usually mean pilots. The shelves are full of reports on captaincy, discipline, sleep, monitoring, simulators, the dangers of drugs and drink, and many other subjects. Incident-report ing, for example, is almost exclusively by pilots and air-traffic controllers. The maintenance departments and manufacturers' design offices are very well posted with defect reports; but very few human-factors stories come out of the hangar. For some reason mechanic error isn't as familiar an expression as pilot error or design error. Of course, "mechanic error" would be a term as over-simplified as pilot error or anybody's error: every acci dent is the result of more than one mistake by more than one person somewhere along the line. And blame is not a safety concept which needs to be widened any further than it al ready is. Nevertheless, a surprising number of the major airline accidents and incidents have been of prime con cern to the maintenance and engin eering departments. PARIS DC-10 We must start with this because, although a design fault was acknowledge^ by the manufac turer, tens of thousands of DC-10 flights had previously been despatched with the fatal cargo door correctly latched. The accident happened in March 1974, killing all 346 occupants when the rear cargo door separated and depressurisation collapsed the cabin floor on to flying control lines. "Mechanic error" was too simple, yet no DC-10 maintenance department failed to share concern in finding and fixing the problem. As always, the accident had been foreshadowed by a number of incidents, including one which had been the subject of a full investigation. CHICAGO DC-10 A DC-10 taking off from Chicago in May 1979 suffered separation of the No 1 engine on rotation and crashed with the loss of all 272 on board and two people on the ground. A crack in an engine- pylon aft bulkhead had been extended by fatigue following impact damage caused by incorrect maintenance pro cedures. TAIWAN 737 Boeing has advised 737 operators to carry out special corro sion checks, in the light of wreckage evidence from the Far Eastern Air Transport 737 accident in August 1981, 60 miles after taking off from Taipei. The recorders stopped at 22,000ft, interrupting a routine radio transmission. All 104 passengers and six crewmembers were killed and wreckage was scattered over a wide area. Aircraft designers have responded to the International Air Transport Association's 1978 document on cor rosion, the message of which was that manufacturers must do better in this area of aircraft life-conservation. The discovery of a corrosion or fatigue problem is probably the biggest dis rupter of budgets known to mainten ance men. The Boeing 767 and 757 are better protected than the much re-skinned earlier Boeing models. In 1965 British Overseas Airways Corporation bought 707-320Cs instead of more Super VClOs, because it estimated that Boe ing operating costs would be lower. There are some British Airways en gineers today who, looking back on the commendably corrosion-free record of the VClO's primary struc ture and comparing it with the heavy replating required by the 707s, might say that the two fleets ended quits in unit maintenance costs. Airline maintenance departments will no longer accept the onset of geriatric structure problems within a short time of delivery. The biggest troublemaker has been metal flooring, especially around spillage areas like galleys and lavatories. Plastic floors, though more expensive, are now stan dard fit or retrofit and last longer. DC-9 PRESSURE BULKHEAD In September 1979 a 27,000hr DC-9 climbing out of Boston at 25,000ft suffered a fatigue failure of the aft- cabin pressure-bulkhead door, re sulting in decompression. The door, tailcone, and a drinks-cart blew out. Fortunately there was no serious loss of control and the aircraft was landed safely. The bulkhead failure was caused by a fatigue crack round the door. The crack had been visible from X-ray photographs taken four months before, but had been missed. Thirty- three other DC-9s operated by seven other airlines were found to have similar cracks. In November 1981 a DC-9-30 broke up at about 31,000ft, nearly half-an- hour after take-off from Acapulco, Mexico. All of the occupants—12 passengers and six crew—were killed. The last radio messages reported de compression followed by loss of con trol. The aircraft was built in 1974. Left The latch-closing system of the old DC-10 oft cargo door shows the over-centre not achieved so that the mechanism is reversible. The linkage on the left is correctly over-centred and irreversible. Right The tailplane-spar fatigue fracture found in the wreckage of the cargo 707 which crashed on the approach to Lusaka when the component broke and separated as full flap was selected. The area was virtually uninspectable Restraining flange\ o lock pin -4 latch actuator 297 actuator shaft torque tube incomplete extensi _of octuator shaft Engagement of lock pins impossible 4 ... .> 230 FLIGHT International, 30 January 1982
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