I believe that B747 do get regularly tear down. They basically remove all the cabins, lots of the conduits and wires, remove the instruments in the cockpit, inspect hidden areas, and reassemble the whole thing.

https://en.wikipedia.org/wiki/Aircraft_maintenance_checks#D_...

A tear down doesn't necessarily involve inspecting every part.

They inspect pretty near every part on a 747 during a D check. Including the toilets.

https://youtu.be/x_yHtfGH0nI?t=36m55s

So far as the HH-53 (the USAF version), when I rode one in the 80's, the saying was that if it wasn't dripping hydraulic fluid, there was something wrong.

I'm sure they do a thorough inspection, but there is nothing in the video to suggest that they inspect literally every part, or anything close to it. Note that by "every part" I mean every component, not every area of the plane. Your remark about the toilets suggests that you may have assumed the latter interpretation.

On each plane it would not be reasonable, but on a few planes it could be done, and would detect defects like the one described above.

Aircraft procedures aren't reasonable. Go and read an accident post-mortem sometime, they're gorgeous. They describe debugging with all the dials turned to eleven. Inspirational.

The reasons planes are so safe is because there are several "unreasonable" things about designing and maintaining aircraft that most engineers would think somewhere between unnecessary and ridiculous.

A lot can be learned from aerospace engineering and the systems engineering used to design air and space vehicles.

Also, a fair amount of the safety of civilian aircraft is because the aircraft owners don't get to skip critical processes, maintenance, etc. They have to answer to regulatory agencies, inspections, etc.

The US military polices itself, so important things can be made optional. They don't have to answer to the FAA on maintenance issues, for example.

During the D maintenance, every part should be inspected. Things like fuel lines should be inspected much more regularly, ideally more often than it would take to rub through a fuel line.

But a visual inspection on a fuel line can be really difficult. I had a motorcycle with a leaky fuel line once, luckily it sprung a leak while warming up in my driveway and I turned off the bike before anything bad happened but it was almost impossible to tell where the leak was without pressurized fuel, the hose looked pristine without positive pressure to highlight the crack.

In race cars, they sometimes 'overpressure' the fuel line (above operating pressure but below max pressure) to check for leaks, I wonder if they ever do that routinely for aircraft.

If the 6 million parts figure is correct, it's obvious that it is not possible to inspect every part of a 747. Suppose we allow 1 minute per part inspection. Then that's still about 11 years of inspection time (without taking any breaks!)

> that's still about 11 years of inspection time

11 person-years. You don't need the same person to conduct all the inspection.

Sure, but you'd need thousands of people to get it down to anything reasonable, even with the highly optimistic 1 minute per part inspection estimate.

I'm open to being corrected on this, but no-one has yet posted any evidence that there is any extant procedure for inspecting every part of a 747.