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Comment by queuebert | Hacker News Reader

I've seen on Toyotas and also at Universal Studios bolts on rides are marked with paint presumably to indicate that the nut hasn't backed out.

Are airliners marked in this way? Is checking the bolts simply a visual inspection, or do the inspectors need to get out a torque wrench?

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Yes aircraft fasteners are often torque marked, and almost all safety critical fasteners have an additional preload locking mechanism. Often these fasteners use mechanical locking features such as cotter pins, safety wire, or safety cable.

Unlike on a rollercoaster, these bolts are hidden within the fuselage behind the cabin panelling so a regular visual inspection to see if they've been loosening wouldn't be practical. During assembly the bolts should have been torqued and then checked and the bolts would only be reinspected when the panelling is removed after 3 years or so.

This is SOP in manufacturing to indicate that a bolt has been torqued to whatever torque specified in the assembly drawing; as an added bonus, if the mark is applied properly, you can also tell at a glance whether the bolt has worked itself loose.

Even better, safety critical bolts on these doors are (supposed to be, at least) pinned.

https://www.youtube.com/watch?v=maLBGFYl9_o&t=523s

Even on light aircraft some bolts will have a safety wire through the head to prevent it from turning. You might even see these on bolts holding the propeller on.

> I've seen on Toyotas and also at Universal Studios bolts on rides are marked with paint presumably to indicate that the nut hasn't backed out.

This is also standard procedure for electrical maintenance inside distribution equipment. Every lug/termination is torqued to spec and then marked to indicate it has been torqued down. This should be done regularly to prevent any loose terminations from causing an arc flash.

common practice in manufacturing to use a paint pen on bolts in assembly lines to check and make sure nothing is backing out aftre maintenance/repair.

Workers are trained and qualified to sign of on their work. Some work is double checked by a co-worker. Some is again checked by QA. FAL work, and loose bolts falling under FOD absolutely, are checked by QA. Or at least should be.

No idea how this can happen, Boeing really has to get its shit together.

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