A worn-out fuel line had been rubbing silently against a bundle of old electrical wires near the front of the cabin – a problem that had gone undetected for years. The same mechanical defect existed inside every Sea Dragon in the fleet, though nobody knew it. Over nearly three decades, the Navy had never required anyone to regularly inspect Sea Dragon wires or fuel lines for damage.
Calling this particular problem maintenance debt is a bit disingenuous. PMCS/PMI could have been performed perfectly for decades and not caught this problem. Peculiar dichotomy in this story; the conflation of design flaw and lack of spare parts and improper maintenance.
We shouldn't underestimate what we don't know about building machines. Maintenance should accommodate time to check for wear on parts we don't expect to, to check things that are different from what we expect them to be. The problem was there for decades and one inspection in one unit over that period would probably have evidenced the issue and added one more item for the maintenance checklists.
It's not like the manufacturer can't schedule a full disassembly of a unit 10 years into its lifetime. Car magazines do it.
> It's not like the manufacturer can't schedule a full disassembly of a unit 10 years into its lifetime
Wait hang on, I was under the impression that a D check (?) did exactly this, every 6-7 years. This is second hand knowledge from a pilot buddy so maybe I'm forgetting something. Also it's on the civvy side of things, maybe the military does stuff differently?
If it's as simple as the military has shittier maintenance checks, then that's a solvable problem.
Edit: ok looked it up, it is a civilian vs military thing.
Very little. In this case, a single inspection (assuming all units were affected) over a period of 20 years would have prevented losses that more than compensate the effort of the added scrutiny.
Also, I like to be the first to know I'm wrong. If I make 100 aircraft and dedicate one to disassembly for study after a quarter of its estimated life, I'll be a .75% investment on better understanding my product. If De Havilland had done that, the stress on the square windows of the Comet would have been discovered before they started falling from the skies and we'd all be flying more beautiful planes.
I was shocked when I found out that, in more than 100 flights, nobody inspected the underside or the leading edges of the shuttle in orbit to check for damage incurred on lift off. They were pretty sure the only dangerous part of the flight was the re-entry.
You say a problem does not exist. You may have good reason to think it doesn't, and, yet, people die because it does.
You absolutely should spend time looking for things you expect not to find, because sometimes you will be wrong.
When you're maintaining an aircraft, a nuclear plant, or anything sufficiently complex or life critical, you should spend a certain amount of time looking for ghosts. You _will_ find them. Your model of an engineered system should include a finite rate of unknown bugs.
This was posted here a few months ago. The article indicated that a change/reduction in training starting in 2003, mainly for cost savings, was coming home to roost. I wonder if similar things are going on in the maintenance area.
I'm looking this up now from a sibling comment, I think that yes every N years a civilian aircraft goes through a complete teardown and inspection, taking >50,000 person-hours of time or something depending on the complexity of the aircraft.
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.
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.
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!)
https://pilotonline.com/news/military/local/distress-signal-...