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Aviation History
1956
1956 - 0498.PDF
498 FLIGHT, 27 April 1956 Fig. 1. The best known of all accident inves- tigations was that carried out on the Comet in 1954. The picture shows the three-dimen- sional reconstruction of wing components. Mr. E. L. Ripleys RAe.S. Lecture Summarized THIS paper, by the head of die accidentinvestigation section of the Royal Aircraft Establishment, was read before the RoyalAeronautical Society on April 17th. Repro- duced here, in summaiized form, the lecturedeals with a most important aspect of accident investigation—the analysis of wreckage. Itprovides fascinating reading for those who, in the author's words, "look at a heap ofwreckage with dismay." Aircraft Accident Investigation "~W DO not intend," the author began, "to go over again the I ground which has already been covered. I am going to deal -•- with what can be learned from wreckage." The evidence of eyewitnesses, he said, even of the aircraft's crew, could be faulty and inaccurate, but the evidence in the wreckage—if it could be interpreted—was a sure and certain guide. Its investigation, when properly done, was a scientific and logical process. The first point to be noted at the site of the accident was in what attitude the aircraft struck the ground. The general layout of the wreckage and the impact marks would show whether it struck at high or low speed, whether it was drifting sideways, or perhaps spinning. Local damage to trees or buildings might give valuable information as to what the aircraft was doing in the last few moments of flight. It was essential during the preliminary examina- tion that every part of the machine should be accounted for, and Fig. 2 (left). Tension failure in a spar boom: This is actu- ally the tension part of a spar failure in bending, but the loading is predomi- nantly tension and exhibits the typical "angles" of a ten- sion failure. Fig. 4 (below). A good illustration of a "fir tree" pattern, showing how the failure had developed from the top. Fig. 3 (below). Bending failure of a light alloy lug: Note the tension failure and the charac- teristic "fir tree" pattern, helpful in tracing the origin of a failure. (See also Fig. 4, right.) if necessary a search should be organized. Knowledge of the dis- position of wreckage could be a valuable asset to the investigation, but this had to be done quickly, as would-be helpers, in bringing fragments to the main site, often forgot whence they came. After plotting the disposition of wreckage on a large-scale map of the area, the next step was to take a closer look at the fragments. A copious series of photographs was always valuable here, al- though such important details as the position of cockpit controls and the readings of instruments should always be jotted down in a notebook. In the author's view the detailed investigation should not be conducted on the site, but the wreckage should be taken where it could be handled with better facilities. To deal care- fully with wreckage was absolutely vital. It would not be amiss to attach a label "Handle Like Eggs" lest vital evidence were obliterated. Once the wreckage had been brought back to the hangar, the first task was to rebuild it, although sometimes circumstantial evidence indicated that only a part need be rebuilt. The author illustrated an example of wreckage-rebuilding familiar to every- one—that of the Elba Comet; one of his illustrations is reproduced in the heading. The work which was performed on the remains of this aeroplane was typical of that done following any major accident of which the cause was obscure. The best way to recon- struct wreckage was to do it three-dimensionally, on frameworks; the aircraft was often laid out on the floor of the hangar in order to sort out the pieces before they were put on the framework. Piecing together the jigsaw puzzle was not as difficult as it might appear. The aircraft's colour scheme provided an important clue, and one soon learned to look for identifying features such as access doors, drain holes, and so forth. Skin gauges, which varied all over the aircraft, enabled wreckage to be sorted into groups, and a use- ful guide was the angle or distance between rivet lines caused by taper or sweepback. Fig. 5 (below, right). This example of a fatigue failure of a steel lug shows the characteristic surface of the fracture and progression lines
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