Nut backed off ball caused accident

BurbMan wrote:

BenK wrote:
Fastening science stuff...cotter pin & castle nut are for different applications

They are for 'not' too tight, but just enough for bearings or some such that needs
to be allowed to 'move'.

Clamping force is NOT the goal, but maintained 'gap' is

Yes that is their role in that specific application but not always.

Look at the head bolts on a radial aircraft engine. All of the bolt heads have a hole drilled parallel to the top and from flat to flat, like this:


Two step fastening process: First the bolts are torqued to spec, second a long loop of safety wire is run through the head of the bolt, the two ends twisted as a pair and then onto the next bolt like this:



On a radial aircraft engine this goes all the way around the perimeter of the engine and includes all of the bolts fastening the head on.

In the case of studs, the nuts are castled and wired in the same fashion.

This NOT a replacement for the correct torque but in addition to. insures that the bolts don't come loose from extreme vibration, cold temps at altitude, etc.

So back to the hitch ball....rather than relying solely on torque to hold the fastener in place, why not use a safety mechanism? Instead of a torque-only spec of 400+ ft/lbs, why not a more attainable 150 ft/lbs with a castle nit and cotter pin?

Also referred to as Safety Wiring. If done properly, when a bolt loosens and tries to back off, it will be tightening the bolt next to it...not just for radial engines, but used throughout aviation period. I fly now, use to be a maintainer, I will tell you that CDI/QA personnel pay especially close attention to the way these procedures are done before you get thrown off the pointy end of a carrier.

Cale