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Comment by zulgin | Hacker News Reader

There is a famous story about how an F16 got grounded because an half inch metal pin was missing from the cockpit canopy. Nobody knew what the pin did or if it was even necessary but you can't fly a plan that 'missing a part'. After several days of being grounded they finally reached out to a guy who had retired 20 years ago who told them the pin was a part of a analogue sensor that had been replaced nearly 30 years ago. Only the pin remained as a vestigial organ since it was part of the airframe design.

It doesn't matter how well you document things there will always be tribal / personal knowledge.

Even if stuff is written down you have to know where to look.

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I babysat for a military fighter jet mechanic when I was young, he said when they dismantled and rebuilt planes there was a drawer for all the spare parts that were left over.

Rap's Law of Inanimate Reproduction[1] strikes again!

[1]: "If you take something apart and put it back together again enough times, eventually you have two if it."

It's crazy to think someone with that complex of a job needs to be babysat

> but you can't fly a plan that 'missing a part'

It’s a great story, but I assure you there is a pretty high percentage of airplanes flying with missing parts and systems placarded as INOP in both military and civilian aviation.

I remember touring the assembly line for military jets.

There were posters everywhere about "extra parts" they called FOD.

FOD applies more broadly than that, as well. Candy wrappers on the runway is also FOD.

It stands for foreign object debris, and means any physical thing out of place where it may cause damage or injury. Because of the nature of jet engines, basically anything can be FOD depending on where you put it.

The 'forest for the tree' here is that when it comes to general operations, a crew chief doesnt generally have the authority to signoff a bird as flight-ready for an unaccounted component. That is the authority of a PMO or a Risk Officer or someone else in flightoos, not a frontline maintenance call. Maybe someone in a maintainence squadron?

Before you can placard something as INOP, you must determine whether the manufacturer and certifying authority have included that part in the Minimum Equipment List or Dispatch Deviation List. Mechanics do both get to determine this at their own discretion. Hence the call to the manufacturer for clarification on the necessity of said pin.

To reiterate, you CANNOT fly an airplane with an undocumented missing part. If the part is documented in the logbook as removed, and it is acceptable to fly that way, then it is not missing.

I have been building and maintaining commercial aircraft for a living for 30 years. What is your experience?

Thanks for asking for my credentials, even though you don’t seem to disagree that lots of aircraft are dispatched with imperfections, so many in fact that there’s a defined process and CFRs to cover it.

Because you asked, I’ve been flying, owning, and overseeing the maintenance of our aircraft for 27 years, including understanding my freedoms and obligations as a pilot and as an operator with regards to the legality of dispatch for imperfect aircraft under both normal operations and under special flight (aka “ferry”) permits. I have spent a lot of time across those three decades both socially and in continuing education courses/seminars with both GA and commercial flight crews and A&P/IAs.

Okay, but did you win the Putnam?

Just the once... (kidding, of course)

Ref: https://news.ycombinator.com/item?id=35083

I don't think you guys are really disagreeing with each other. Just that one is using a colloquial definition of "missing" and the other, a technical one.

An absent (removed) part might be acceptable depending on circumstances, but a genuinely missing part creates hazards and must be ascertained as to its location. A mechanical jam, an electric short, a hydraulic leak, or a Foreign Object Damage to the engine from a piece of metal on the loose can destroy the plane, endanger people and mission. Same concern with tools & bits, can't have any unaccounted for.

Chesterton's fence is strong with this one

Exactly. Framing completely changes this from an absurd story causing pointless grounding due to loss of institutional knowledge, to an example of good judgement (or protocol) in the absence of knowledge and acknowledgement of the risk of unknown consequences.

What's being ignored is the 1/100 of these stories where this judgement pays off, saves aircraft and lives that make the other 99 worth while.

> Even if stuff is written down you have to know where to look.

That's one of the things I love about AI: It's excellent at figuring out where to look, because it can digest so many documents so much faster than a person.

Yeah it’s great to point an AI at a very detailed and specific engineering manual and have it distilled down into bullet points. There’s certainly no room for information loss in that plan! /s

Plus everything important is always written down.

It’s more true in aviation than anywhere else (except maybe space flight), but still.

And if it's written down, it's accurate. 100. Percent. Accurate. /s

And because it's accurate the AI will know how to weigh that accurate information against other accurate information in such a way that it will give you a great answer without any help. In other words: any amateur will be able to do aircraft maintenance! What can go wrong? /s

You know, if I had to make that bet, I would choose airline maintenance manuals as the test case.

Have you seen the maintenance manuals on an aircraft production line? They're in 3-ring binders, so you can take out and replace pages. They are constantly being corrected and updated. The industry recognizes they're never at 100% (and to their credit mitigation is part of the process).

I hate AI as much as anybody, but claiming that it's not useful for "distilling volumes of data into a short list of places to look first" is silly.

It’s very good at that, but aeronautical engineering and maintenance is the last place you’d want that.

GP did not suggest anything of the kind, though. They talked about "figuring out where to look" which very different. In that kind of use, it doesn't really matter that the model might hallucinate or draw faulty conclusions, as you're not using it figure out what to do, how or why. The only thing it is telling you is where some information is located, after which you go check it out from the actual source of truth. If the reference turns out to be wrong, you'll notice immediately.

For all our sakes, I hope your career never takes you anywhere near an airport.

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