Talk:MacRobertson Miller Airlines Flight 1750

Probable cause
I have just added some info taken from the Accident Report on the spar re-booming technique and subsequent problems on the accident aircraft.

Reading between the lines, it's not difficult to deduce the probable sequence of events. The aircraft was re-sparred and during this the mounting holes for the nacelle rear attachment were drilled in the new lower boom. For some reason these were drilled slightly mis-aligned. On re-assembly of the wing, when the nacelle was offered up to the wing it was found that the holes for the mounting bolts did not fit - if a new nacelle rear mount had been used this would not have mattered as the new part would have had its holes drilled to match the slight mis-alignment. However, the maintenance personnel decided to re-use the old part that had just come off the aeroplane, as this has been made permissible by the manufacturer as this particular part had been found to not be as susceptible to fatigue as had been initially thought when the aircraft design was new. Because the bolts would not pass through the new mounting holes under the wing, rather than scrapping the new replacement boom, it was decided to use a drill to remove the excess material preventing the bolts entering the holes. This was done after the bushings had been inserted and this drilling scored the inside of the bushings. It is likely that the drill stuck/seized on at least one of the bushings and this destroyed the interference fit of the bushing within the boom, making the bushing loose. At this point an attempt at assembly was made, however when the bolt going into the damaged bushing was inserted the bushing was pushed halfway out of its hole in the spar boom. An attempt was then made to swage the bushing, using some sort of punch or die and a hammer, to get it to remain tight within its hole in the spar boom. Unfortunately this process destroyed the resistance to fatigue that the additional bushings were meant to confer in the first place - the bushings were a later design addition intended to increases the fatigue life of the spar by isolating the bolt loads from the aluminium spar material. Because the mountings were concealed within the wing/nacelle structure, the mistake was not noticed by maintenance personnel in the subsequent years prior to the accident.

I haven't added any of this to the article as it's mainly conjecture on my part. — Preceding unsigned comment added by 80.4.57.101 (talk) 11:52, 1 December 2011 (UTC)


 * I agree with much of what you have written, but there is one aspect that I disagree with. New booms were supplied with all holes drilled and all bushes inserted.  Drilling of holes in the booms did not have to be done by maintenance personnel.  It was the holes in the nacelle mount fitting that had to be drilled by maintenance personnel to match the bushes in the boom and allow proper alignment of the nacelle with the wing.  Holes in the fitting weren't bushed.  I have deleted the sentence saying the holes in new booms had to be drilled by maintenance personnel - see the diff.


 * I agree that it looks like maintenance personnel used a twist drill to align the holes using the steel bushes as drilling guides. It says as much as this on page 14 of the Accident Investigation Report where it states: In this situation it is conceivable that some attempt might have been made to improve the alignment of some of the holes by passing a 5/16 inch drill through the fitting into the bushed hole from below.  Dolphin  ( t ) 02:14, 30 March 2012 (UTC)


 * OK - thanks for the reply. You're almost certainly correct. I hadn't realised that they had eventually re-used the original nacelle mount fitting removed during the initial re-sparring some years earlier, with a new (i.e., un-drilled) part used in the intervening years.


 * ... and just a thought - I wonder if the high temperatures out in the sun in the Antipodes might have had something to do with the difficulty in alignment, with a part (the relativity long tubular nacelle mount fitting) that had perhaps been stored out of the sun at the back of a hangar for several years long enough to get nicely cold-soaked, compared to an aeroplane that may have been sitting outside in the hot sun for several days. I suspect however, the change in dimensions would have been insignificant, and I expect the accident investigators already thought of that scenario at the time anyway. — Preceding unsigned comment added by 80.7.147.13 (talk) 18:37, 23 May 2012 (UTC)


 * Thanks for your interest in this accident! In Australia, unfortunately, there is no likelihood of anything cold-soaking at the back of a hangar for more than a few months.  In summer, every part of a hangar gets flaming hot, even in Melbourne where this work was carried out in Ansett’s facilities.


 * On page 25 of the Accident Investigation Report, middle paragraph, it says: This fitting was examined and the spacing of the holes was sufficiently different from the spacing consistently established in new spar booms to indicate that some difficulty must have been encountered, during the spar boom change in 1964, when it became necessary to secure the fitting to the wing structure by passing the five bolts through it, through the doublers and wing skin and through the lower boom of the spar. The misalignment of the holes was such that the 5/16 inch bolts could not have been passed through all of these components unless some action was taken to improve the alignment.  One of the possible remedies for such a situation would be to pass a 5/16 inch drill through the holes from beneath the fitting so as to remove some of the material in those bushes which were preventing the passage of the bolts.  Dolphin  ( t ) 22:53, 23 May 2012 (UTC)


 * OK - thanks once again. Thinking about it, I realise that it would also be pretty hot inside a hangar all the time out there. I suspect that the mis-alignment then may have been due to the bolt holes in the parts being at either end of their allowable tolerances.


 * I find air accidents interesting, apart from my interest in aviation in general, because of the sometimes convoluted chain of events that lead up to them. With hindsight it's often apparent what went wrong, but it's usually not so easy at the time to see the possible unfortunate effect and consequences of people's decisions and actions, whether in design, or operation. Unfortunately as aircraft and systems in general get more and more complex, they tend to act as 'error amplifiers', whereby a small mistake in one place subsequently leads to catastrophic failure of the system as a whole. Good design and maintenance should minimise this, but there is a large element of randomness to accidents which probably cannot ever be eliminated.


 * So, while losing a wing is unsurvivable, in so many accidents it often just comes down to bad luck while attempting to cope with unforeseen circumstances. I suspect that it always will. Personally I think that commercial airliners started to become ludicrously over-complex to design, build, operate and maintain with the ones introduced back in the 1960s, but that doesn't look likely to change as it appears to be what the airlines and their customers want, i.e., big, complicated (albeit very efficient) airliners that allow them to offer cheap fares. And, as for the latter, why not. The fabrication of more and more large parts, such as complete wing assemblies, fuselage halves/sections, etc., in carbon fibre and other composites may help, as the reduction in part numbers in itself will hopefully reduce the error 'nodes' around-which failure may occur. But that's just my opinion. — Preceding unsigned comment added by 80.7.147.13 (talk) 10:18, 25 May 2012 (UTC)


 * BTW, this aircraft (as VH-TVB) appears (very briefly) in a 1959 Farnborough Airshow film on YouTube here: - it's at 0.49 into the video.  — Preceding unsigned comment added by 80.4.57.101 (talk) 21:24, 3 March 2012 (UTC)