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FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

reuters.com

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Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#111

Post by teh_klev »

kayfox wrote: post #87
nabilhat wrote: post #70

Earlier quoted context omitted.

Who even uses calipers for critical precision? Calipers are for dimensions machinists append with -ish, as in four thousandths-ish. Important dimensions deserve a micrometer, especially the feeler guage that just said you need to tell your boss to scrap a 737. Decent machine shops even have different classes of micrometer; there's the one you carry in your pocket, and then there's the fancy set locked up in your boss…

You don't scrap a 737 for some worn out parts.

Not that I want to be pedantic, but that's a rather sweeping statement. The decision to scrap would depend on things like the number of flight hours and takeoff/landing cycles on the air frame and the number of other worn parts, hitting meantime-before-failure on large numbers of parts/assemblies, such that it may be more economical to scrap.

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#112

Post by bluGill »

MrBuddyCasino wrote: post #47

This may be a dumb question, but why use materials that can corrode on such an important part? Just use stainless steel (or AL or TI), problem solved?

Stainless doesn't corrode, but it tends to corrode any other metal it touches. Depends on alloys and a bunch of other factors, but all stainless isn't the answer either.

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#113

Post by Gibbon1 »

elliekelly wrote: post #73
rlpb wrote: post #19

Earlier quoted context omitted.

If it's a gap between two parts that they're measuring, that's as simple as a feeler gauge: https://en.wikipedia.org/wiki/Feeler_gauge . The set pictured there looks like it goes down to 0.05mm.

Perhaps an odd question from someone who only just found out that feeler gauges exist - do they periodically calibrate or confirm the measurements of the gauges? If someone is sticking the same gauge into tight spaces all day wouldn't it wear down, even slightly, and alter the reliability of the measurement?

In aerospace everything like that is traceable and calibrated on a schedule. Traceable means that there is paper work that shows what it was calibrated against. Which itself is traceable to a NIST standard. The difference between traceable and ordinary measurement equipment is a couple of extra $.

Put is this way one time I found a set of hex torque drivers with cal stickers on them at a surplus place. So when I say everything I do mean everything. So yeah a feeler gauge should be traceable.

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#114

Post by aunty_helen »

cartoonfoxes wrote: post #82
kube-system wrote: post #31

Earlier quoted context omitted.

This tool would be capable of performing that measurement with 0.001" accuracy. https://www.harborfreight.com/feeler-gauge-32-pc-63665.html Someone performing maintenance in their garage on an internal combustion engine would encounter the need to measure the same tolerances, for example, adjusting valve clearances. This is a common and accessible measurement task.

Strictly speaking, it wouldn't. One of the interesting things the aviation industry deals with is a need for traceability of the metrology all the way back to NIST standards. That extra test, certification, and paperwork has a price. Compare the harbor freight example with this one: https://forneyonline.com/feeler-gauge-set-26-leaves-0015-to-...

I'm not sure where you got this idea from, sounds like a lot of work.

It would be much easier just to calibrate the tool before putting it into service. And given that there is a routine calibration schedule for measuring equipment, there's no need to have some NIST paperwork certifying the metallurgy of the brass rivet holding your feeler gauge together.

The two tooling engineers I sat next to when I worked at a jet engine MRO would buy any tool they wanted from their parts catalogue. I can't remember the name of it now but it was yellow covered and about 6 inches thick.

They would buy the same tools you could get at any respectable hardware store. Snapon, Koken, TengTools were common. They bought good quality so it lasted, not so they could get NIST certificates with them.

In the engine manuals, for specific jobs, there would be specific tools you would need to use. These would be listed by part number. If you used any old torque wrench when the manual specified a particular part, you weren't in compliance. This could be picked up by an aviation authority when your paperwork was audited. Or of course, if you have an 'escape' where an engine gets put on a plane and then stops mid flight (second worst case scenario).

The same goes for the calibration of the tool, each time you torque a procedure you need to fill out the paperwork with the tool # that the engineers will have engraved on the side of it. If the records show that tool is overdue for it's calibration when it was used, best case scenario, engineer doing the procedure gets told off, tooling guys get a 'finding' and have to improve their system of tool tracking. Worst case scenario, people die. Which could result in the Quality manager getting thrown in the clanger.

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#115

Post by acheron »

mmanfrin wrote: post #92
Contax wrote: post #91

Earlier quoted context omitted.

And why not just "NG and Classic"? Really curious, I see this replacement of "and" for a comma in a lot on headlines, and I don't know why or where it comes from (English is not my first language). Is there a name for this?

Most english speakers also wouldn't be familiar with the term, but it is called 'Headlinese'. https://en.wikipedia.org/wiki/Headline#Headlinese

Imitating this style is a good chunk of the Onion's humor. E.g., "Congress Approves $4 Billion For Bread, Circuses"

https://politics.theonion.com/congress-approves-4-billion-fo...

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#116

Post by steffan »

adenozine wrote: post #48
kube-system wrote: post #43

Earlier quoted context omitted.

They're measuring it to ensure corrosion hasn't thrown it out of spec, right? Not that it wasn't manufactured to spec?

Excellent point, shows you how much of an engineer I'm NOT . That's probably a big point too. Surely there's some sort of chart they've made for all these parts and how fast they're allowed to decay, given some number of flight-hours?

> given some number of flight-hours?

I think the issue here is the lack of flight-hours. These parts were designed and specified for an in-use plane, not one that sits around.

An airplane is an extremely expensive asset and they are typically almost constantly in service. It's very rare for one to be idled for months at a time.

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#117

Post by Gibbon1 »

na85 wrote: post #67
bamboozled wrote: post #39

Earlier quoted context omitted.

I love that out of all the more complex ideas about what may have been used, it turns out likely to be a solid piece of metal with of a given thickness, couldn't get more simple than that.

That's what real engineering is about: the simplest tool or process that will get the job done. Despite what we see on the web more and more, this principle applies to code too. It shouldn't be about stacking up layers of complexity for no good reason.

Somehow your comment reminds me of a pissing match I saw between a young aerospace engineer and an old retired one. The old guy was right in his argument that it doesn't matter what the constraints on materials and dimensions are, it that they come from somewhere and are documented.

His example was designing brackets for a Indonesian construction company that was using locally sourced tropical softwoods for constructing buildings. The brackets were designed to be made with 'steel' and the tolerances were compatible with a hungover guy running a drill press.

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#118

Post by a2tech »

elliekelly wrote: post #73
rlpb wrote: post #19

Earlier quoted context omitted.

If it's a gap between two parts that they're measuring, that's as simple as a feeler gauge: https://en.wikipedia.org/wiki/Feeler_gauge . The set pictured there looks like it goes down to 0.05mm.

Perhaps an odd question from someone who only just found out that feeler gauges exist - do they periodically calibrate or confirm the measurements of the gauges? If someone is sticking the same gauge into tight spaces all day wouldn't it wear down, even slightly, and alter the reliability of the measurement?

Yes. And places that deal with these types of tolerances will typically have a person who's job is to simply verify and replace gauging. If a gauge doesn't have a documented test verifying its accuracy, then it has to be assumed to be inaccurate and any parts or tests based on results provided by the instrument need to be redone or the part scrapped.

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#119

Post by a2tech »

Gibbon1 wrote: post #113
elliekelly wrote: post #73

Earlier quoted context omitted.

Perhaps an odd question from someone who only just found out that feeler gauges exist - do they periodically calibrate or confirm the measurements of the gauges? If someone is sticking the same gauge into tight spaces all day wouldn't it wear down, even slightly, and alter the reliability of the measurement?

In aerospace everything like that is traceable and calibrated on a schedule. Traceable means that there is paper work that shows what it was calibrated against. Which itself is traceable to a NIST standard. The difference between traceable and ordinary measurement equipment is a couple of extra $. Put is this way one time I found a set of hex torque drivers with cal stickers on them at a surplus place. So when I say…

Yup. Traceable all the way back to the batch of material the part is made of. For every part in the plane. One of my customers makes parts for Rolls-Royce engines for the aviation industry and have to store certs and manufacturing records for even the smallest part. That includes certs on each step of manufacturing and material. Its pretty intense! During crash investigations they can be called upon to provide the full audit trail. Now imagine the amount of paperwork that is produced during an investigation when every nut and spring in a plane has the same amount of associated paperwork produced.

Re: FAA issues emergency directive on 2,000 Boeing 737 NG, Classic planes

#120

Post by ryandrake »

kube-system wrote: post #99
cartoonfoxes wrote: post #82

Earlier quoted context omitted.

Strictly speaking, it wouldn't. One of the interesting things the aviation industry deals with is a need for traceability of the metrology all the way back to NIST standards. That extra test, certification, and paperwork has a price. Compare the harbor freight example with this one: https://forneyonline.com/feeler-gauge-set-26-leaves-0015-to-...

I just meant it's 'capable' in context of the above question of engineering capabilities. But you're very right that aviation requires expensive safety and compliance procedures on top of that.

Yea, they are both capable of doing the same job, but one comes with a $104.01 piece of paper that proves that a clerk in an office stamped another piece of paper and filed it away in a cabinet, which makes it legal to use with a certified airplane.
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