Originally Posted by
H Peacock
Getting a bit more into the technical aspect of the shackle and bolt. I agree that, as stated early, It's very surprising that MB didn't design a bolt with a shoulder that the nut was tightened up against. I've been a dreadful aviation hoarder/scavenger for years and have played with plenty of MB products. The innovative design and build quality is staggeringly impressive. So the use of a 'normal' off the shelf bolt is very surprising. (I know MB probably made the bolt specifically.
I am slightly puzzled about the torquing up of a locknut & bolt where you don't want the nut to bottom-out on the thread or even against a fitting the bolt goes through. In other words you are purely relying on the resistance to the 'locking' ability of the nut. A brand new nut is invariably going to be stiffer than a well worn one. How do you calculate a torque that caters for both cases? Clearly, if a normal nut were used you could only achieve a tightening torque when the nut is up against the fitting! If the specified tightening torque is less than the resistance of a worn nut screwed along a continuous thread, then you can only achieve that value when the nut impinges on something else.
Although I have said it already I'll say again. That bolt was never meant to be fastened/unfastened all the time. For the Ist half (or more) of that seats life it's possible it was never undone. Work would only have been ever done in the seat bay and opening the shackle was done by releasing the BTRU. I would be interested to know who authorised 1st line rectification of ejection seats after the demise of seat bays. I would like to think this would have been discussed at MB and recorded decisions made.
Edit, a distant memory but I'm sure at servicing we tested the opening of the shackle we a spring balance measurement, had to be under a certain pull weight.