That’s pretty incredible. After a heavy maintenance breakdown, what percentage of the plane gets replaced? Or is everything already on a routine maintenance schedule so the intention is to visually identify unexpectedly failing parts?
IIRC every bolt's torque value needs to be logged any time it's (re)fastened. At least that's true for aircraft engine maintenance, not sure if it applies to the assembly process of the airframe, I'd sure hope so!
The Max 9 has been in service since 2018 though, I think if it was a design issue it would have occurred before now. This seems like a Manufacturing QA “escape” to me. Some bolt was either not installed properly or not tightened to the proper spec, QA did not catch it
> The Max 9 has been in service since 2018 though, I think if it was a design issue it would have occurred before now.
That's a bit of a leap. If the bolts are e.g. too soft and have worn out in use, that would be a design issue that would only show up after a period of use.
I'm not sure what the standard is in the aviation industry, but things like data-logging torque wrenches exist, and are used in other industrial applications.
Does wiring bolts actually help? I feel like if a bolt is going to come loose enough such that the wire is all that is holding it in then you have a big problem already. The wire is just delaying the inevitable.
A bolt is either fastened or it isn’t. If the wire is all that’s left to hold it, then it isn’t fastened and your parts are being held together with a very weak piece of wire.
The safety wire comes in to prevent a loose bolt from gently unscrewing itself further and completely disassembling itself (which can happen with vibration).
You're much better off with a loose bolt, than a missing one. It'll hopefully make itself known somehow (maybe even just visual inspection) while still remaining somewhat attached, which is better than nothing.
Thanks for the explanation. Does that mean a correctly wired bold should have wires loose enough to allow a loose bolt to give itself away — either through rattling or becoming visibly undone?
When I searched for images of wired bolts just now I saw many examples where the wire is done up quite tightly, which doesn’t seem right.
There's different kinds of bolts that get wired, with different kinds of goals and results.
My only experience is wiring bolts according to the rules for club racing motorcycles.
Some things, like oil sump drain bolts for example, wiring them will stop them backing out so far as to fall our, and while it will probably weep oil if it loosened enough to take ups the writing slack, it wouldn't dump all the oil out quickly.
Other things, like axle bolts, if it backs out enough to take up the wire slack, it'll have lost its clamping pressure and that's bad, but not immediately catastrophic. The major axle loads are all in shear so the wheel won't fall off, it'll just get more floppy than it's supposed to be. Long term it'd be bad and cause wear to the point that something would eventually fail, but it'd get you to the end of the race most likely, and hopefully the rider will have felt something odd and gone looking or a post race inspection would have caught it.
Happened to me once when I was racing an R6 6 years ago. I didn't torque the rear wheel nut, but had put my safety wire clip back through the axle so the nut couldn't back off. Got a warmup lap in and started in on a fast lap during a practice session, and it was immediately obvious something was wrong. Limped back into the pits and found the loose nut. I said a quick prayer to the wiring rulebook (and the people who crashed before that rulebook existed), and inspected everything on the bike.
