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Aviation History
1951
1951 - 0458.PDF
286 FLIGHT, 9 March ACCIDENT INVESTIGATION How causes are found and cures applied: A. Cdre. Vernon Brown's Lecture to Licensed Engineers Found three miles from a crash, this piece of plastic material pierced bya splinter of wood gave the clue to the cause—an airscrew breakage. THE investigation of aircraft accidents is sometimes aptto be regarded by the uninitiated as merely anotherinstance of Officialdom's desire to pry, interfere, pre- pare memoranda and give employment to large staffs. In actual fact, as most readers of this journal are aware, it is a valuable and rewarding science and one which has un- doubtedly been the means of saving a great many lives and much valuable property. Some of these positive results, and the methods by which they are achieved, were lucidly explained by the Chief Inspector of Accidents, A. Cdre. Vernon Brown, C.B., O.B.E., M.A., F.R.Ae.S., R.A.F. (ret.), in a lecture to the Society of Licensed Aircraft Engineers, given in London on February 24th. A summary of his paper follows. After defining an "accident" as opposed to an "incident,"A. Cdre. Vernon Brown explained the two methods of investi- gation of civil accidents adopted in this country : (a) by his depart-ment, and (b) by a Court of Inquiry. On notification of an accident to the Minister of Civil Aviation, the preliminary particu-lars are quickly obtained in order that a decision may be given as to whether an investigation of any kind is, in fact, required.If the answer is in the affirmative, members of the Chief Inspector's staff* go to the scene and collect all possible evidence. A prelimin-ary report is then prepared and the Minister decides whether (a) an ordinary investigation or (£>) a Public Inquiry should beheld. In the meantime, if the evidence suggests the necessity of introducing immediate safety measures, the appropriate depart-ments are advised. If the Minister decides upon an investigation he advises theChief Inspector accordingly. The analysis of the evidence is continued, and the investigation is considered complete when theChief Inspector has made his report to the Minister. If blame is to be attributed, then certain requirements must be observed toensure that the legal position of those involved is duly safeguarded. The Minister also decides whether a report should be published—as in the case of those accidents on scheduled or charter passenger flights from which useful lessons are likely to be learned—ormerely made privately available to any interested persons requiring information. Commenting on what sometimes appeared to be unnecessarydelay in setting up a Court of Inquiry, the lecturer reminded his Certain accidents that resulted from wooden-airscrew breakages were found to be due to failure in the region of the blade-tip sheathing. audience of the inevitable difficulties attendant upon nominatinga president, assessors and counsel. He went on to explain that, as head of the Accidents Investigation Branch of the M.C.A., he wasdirectly responsible to the Minister. "I would like to emphasize," he said, "that no Minister has ever exercised pressure on me ofany kind whatsoever, and that I have always been left free to express my views without fear or favour. The A.I.B. has, in fact,been treated as if it was independent of the Ministry." Discussing investigation methods in detail, the air commodoreshowed illustrations of the extreme types of wreckage that might be encountered, varying from an aircraft that had fallen in a flatspin and suffered comparatively little damage, to high-speed crashes and to mid-air structural failures which might spreadwreckage over miles of countryside. Since the clue to the cause of the accident very often lay in thewreckage, it was most important that, before the investigators arrived, the crash should be properly guarded against souvenir-hunters or crowds who might tread wreckage into the ground and, incidentally, obliterate impact marks. To show that vital evidence was not always discovered in the»wreckage itself, the lecturer illustrated a small piece of plastic! material found nearly three miles away from a crash; in it wasembedded a splinter of wood. The plastic material was identified as part of the nose of the aircraft, and the splinter as coming fromthe airscrew, thus indicating that an airscrew breakage had been the primary cause. A. Cdre. Brown then went on to show various examples ofmetallurgical failure, and explained how fatigue failures could usually be distinguished, by a trained engineer, from breakage asa result of the crash impact. Wood failures, he said, were a study in themselves; and the fibres often gave a clue as to whether failureoccurred in tension, compression or bending. Glued joints formed a special study, and although the A.I.B.could generally be sure if a joint had been badly glued, they pre- ferred to seek diagnosis from specialists. Experience usually showed what various marks on wreckageindicated. For instance, damage caused by a bird striking a leading edge could usually be easily identified by the presence of feathersor blood. Sometimes the tailplane might be damaged by a heavy object such as a dinghy-inflation bottle (during the war a seriesof accidents had occurred through dinghy-compartment covers coming adrift); in another case, a tailplane was found at anisolated position in the wreckage trail, and showed some peculiar damage that could not be reconciled with the fact that the tailplanehad fallen upon grass; it was eventually found that one of the undercarriage doors mated perfectly with the damaged area.showing that the door had come off in flight. The examination of wreckage was, of course, only one of theA.I.B.'s tasks. Background information was always required, such as the nature and history of the flight, weather conditions (fore-cast and actual), briefing details, crew histories, aircraft documen- tation and loading, navigational and other aids carried, groundaids available, and so on. Because human error might be closely bound up with technical factors, their relationship had to becarefully examined; nor must the investigator forget the possibility of crew fatigue, perhaps contributed to by noise, vibration,temperature or inadequate cockpit lighting. It might, therefore., be very important to obtain evidence from survivors, though muchdelay might occur before a survivor was well enough to be inter- viewed. Other delays arose from the necessity of making laboratorytests on parts of the structure. The lecturer then went on to give a number of examples—from an earlier paper he had read before the R.Ae.S.—on the beneficial effect of accident investigation on aircraft design. Heinstanced the use of slats as an anti-stalling measure. While they had been effective many years ago on the smaller types of aircraft, * The staff, explained the lecturer, consists of Inspectors, who have apractical flying background, and Investigators, who are primarily engineers.
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