Originally Posted by
First_Principal
Thanks A0283, my reading of the report is that the 'correct' nut was used, just that it had not been manufactured to the requisite tolerances by the overhaul supplier (that is to say, the next size up nut had possibly been supplied as 'correct')?
I've not worked on these, is the nut fitted during replacement of the assembly on the a/c, or is it kept intact as part of the assembly supplied by the manufacturer? If the former I'd be a little surprised that the engineer fitting the nut didn't detect there was something wrong given the nut minor dia was circa 1/16" larger than it should have been - or is that being unreasonable?
Reading between the lines of the report, it would appear that the November 2019 overhaul (the one allegedly carried out by Kelowna) included an approved repair to the swivel attachment to the MLG strut. The repair involved recutting the threads on the swivel for a second time (having been done originally in 2008), which of course then required a correspondingly (further) undersized nut to be used during reassembly. It appears that instead of a 1/8" undersize nut being used, a 1/16" undersized one was fitted similar (or possibly even the same one) as that which had been removed.
In effect, most of the retaining force was then being provided not by the nut, but by the locking bolt, which sheared under landing loads, allowing the swivel to pull free from the nut and detach from the gear leg, with the inevitable result.
It's certainly not the first time that mismatched threads have resulted in failure of a component (a certain One-Eleven springs to mind) and it probably won't be the last.