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> But maintenance people in aviation aren't really ever exercising those creative problem solving skills

This is the opposite of what happened. The engineers were confronted with a novel and unexpected problem, and instead of following procedure (which they lacked access to) they applied "creative problem solving skills". From TFA:

> Although it was possible to install the post-SB fuel lines and hydraulic pump with a pre-SB hydraulic tube, the tube would rest against one of the fuel lines at a point where it rounded a 90-degree bend close to the pump. Aware that the plane could not be dispatched unless there was clearance between the tubes, the technicians torqued a nut on the end of the hydraulic tube until it rose approximately 0.635 mm off the face of the fuel line.

Torquing a nut so that the hydraulic tube isn't technically rubbing against the fuel line is pretty creative and seems to solve the problem. But it didn't take into account pressure and vibration while in flight, and almost caused the death of 306 people.

I'm amazed they can measure the distance between two real non-fixed components down to a few micrometers (they wrote 0.635mm, implying somewhere between 630um and 640um)

If 0.635mm (an odd number itself which happens to be exactly 1/40th of an inch, or "25 thous" in American sizes) and they let it go that sounds really odd. That's literally the size of a grain of sand. If the concern is rubbing, sure that implies it will move during flight.

0.635 mm is indeed an odd number. The thickness of a piece of 80gsm paper is 0.065 mm, so maybe what is meant is "about the thickness of ten sheets of paper"...?

It's precisely 0.025 inches.

Who else thinks that if a tolerance of the thickness of a sheet of paper, in a mechanic/maintenance setting, could cause the death of over 300 people, that there's a striking lack of fault-tolerance in the design.

It sounds to me like they stuck a machinists shim in there, effectively a bit of precisely measured metal.

Shim feeler gauges would be readily available in most shops checking wear on moving parts. 0.0025 inches (0.635mm) was included in the first high quality (gearwrench brand) set that I looked up online.

Plane maintenance involves a lot of precise and specially designed tools.

I wonder if this nut, if not every nut on an ETOPS airliner (or in general), has a specific torque value. If adjusting the torque can open up a gap, presumably doing so could close one as well.

I don't think this is true at all

> These are the kinds of failures you get when you try to proceduralize everything with foolproof procedures

> Had the technicians

The report makes it clear that the problem was their lack of access to the relevant details, not that the process was defective. If they had seen the need to replace the hydraulic hose, they would have presumably changed it or flagged the problem to someone higher up.

> The maintenance people didn't even know they were making a judgement call.

It seems like they did. If you replace a part and something is touching, you are not trusted in aviation to try and make some space with a bit of fiddling for exactly this reason. They did make a judgment call. If they had relied on the process, again, they could have queried why the new pump was touching when the old one wasn't.

"Follow the process" is because this is like the tenth example of engineers and maintenance personnel trying to ignore the instruction booklet and nearly getting hundreds of people killed.

"Read and follow the directions exactly" is a rule that is written in blood.

There was a shortcut: "But if they had looked at the text of the SB, they would have realized that they missed a step: they were also supposed to replace the hydraulic tube which attached to the pump." With the old tube, the clearance was insufficient to avoid contact while in use.

> These are the kinds of failures you get when you try to proceduralize everything with foolproof procedures, checklists, run-books, processes, etc.

Aviation safety is utterly dependent on procedures, checklists, run-books and processes. The fact that things sometimes fall through the cracks is no argument against them.