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Aviation History
1985
1985 - 2218.PDF
AIR TRANSPORT Air-India wreckage: recovery is the problem CORK Wreckage of part of the Air- India Boeing 747 has been found on the Atlantic sea bed, presenting the crash investigators with the major problem of salvage. The section of the aircraft found so far is a part of the fuselage with windows. Bodies have been detected inside it. The wreckage was discov ered by a television-carrying unmanned submersible deployed by the French cable- laying ship Leon Thevenin. It is within 1| n.m. of a central search area covering 10 n.m. x 1 n.m., and lies at a depth of just over 7,000ft. Unconfirmed reports from the Leon Thevenin at the weekend said that a substan tial amount of the 747 wreck age, including the tailplane, has been located along a 41 n.m. stretch. Intermittent signals, origi nally discounted as signals from the locator beacon on the flight data recorder (FDR) have now been accepted as possibly being such signals. The beacon unit is designed to operate to a depth of 12,000ft, and to emit "ping" signals once a second for 28 days. Earlier uncertainty had been caused by the irregularity of the signals being received, but now that is thought to be caused by shielding or some other factor. However, there is a possi bility that the FDR will be of little use, even if it is recov ered. There is some evidence that whatever catastrophe caused the aircraft to crash caused an instant total elec trical failure (Flight, last week, page 3). If the electrical failure was total, and if the failure occurred at the begin ning of the whole disaster sequence, then the FDR would have ceased to func tion. The locator beacon may have its own integral power source, but the FDR takes its power from the aircraft's generator-fed emergency bus bar. It is not on the 747's battery busbar because its power requirement is quite high, and it would cause the battery to run down too fast in a situation where the crew were relying on battery power alone. Examination of the 131 bodies recovered so far, and examination of the small amount of wreckage retrieved, gives no indication that a bomb explosion was the cause of the accident, though an explosive decompression certainly took place at some stage in the disaster sequence. However investigators will not rule out a bomb as a pos sible cause because they acknowledge that it would supply a neat answer to all the questions, and there is no other probable cause for which positive proof is emerg ing. Sections of wreckage that have been recovered are believed to have come from the ceilings of two of the luggage/freight bays, though from which two is not certain. There is no evidence of an explosion on these sections, which puts a strain on the bomb theory without actually eliminating it. If positive evidence of bomb damage does not emerge as investigations continue, it becomes progressively more important that the FDR, the cockpit voice recorder, and as much of the wreck as possible are salvaged. Boeing will hope to find that any structural failure which caused an explosive decompression was caused not by a design fault or by corrosion, but rather by abnormal stress of some kind. Air-India will hope to find that any structural failure which caused an explosive decompression was caused by stress rather than mainte nance problems, and that any abnormal stress was not caused by the aircraft's devi ation from its proper flight profile, after the manner of the China Air Lines 747 over the Pacific in February, though that aircraft survived its aerobatic sequence. (Flight, March 2, page 2). Nothing as large as the pieces of aircraft wreckage which are on the Atlantic sea bed has ever been recovered from a depth as great as 7,000ft, unless in a covert military operation. So despite the importance of recovery it still remains uncertain whet her the wreckage can actually \ be raised in a useful form (ie: not further severely damaged^ by the recovery operation). Canada has a boom defence vessel on the way to the search area to help in recov ery. The US Navy has a vessel on station carrying out search | operations. The French cable- 4 layer Leon Thevenin is using I Cable & Wireless' Scarab submersible to obtain the side-scans and television pictures of the wreckage which have so far been discov ered, and to carry out further searches. It was Scarab which found the wreckage in the first place. Apart from the unknown difficulties of raising the) wreckage, there is the expense of doing so. The US Navy has ; come up with a figure which, in salvage terms, is reckoned to be cheap: $2 million to get the equipment on station, and $200,000 a day thereafter. Theoretically, it is the Indian Government which would request such an operation, and which would pick up the tab for it and for the search as well. But India could not reasonably afford it. The chances of recovering the FDR seem to be improving. The signals from' its locator are in the vicinitv^ of the discovered wreckag^L What the investigators hope for is not only recovery, but that the recorder will actually.) have a tale to tell if it is recovered. If evidence of sabotage remains undiscovered, then it becomes even more important to recover the FDR and the wreckage to determine the accident's cause. Neither Boeing nor Air-India will be able to relax until the cause is known FLIGHT International, 13 July 1985
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