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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

#61

Post by nogabebop23 »

adenozine wrote: post #16
wwv25 wrote: post #7

One of the inspection checklist items: Measure the clearance between the flapper bushings at both locations on each engine bleed air 5th stage check valve. If the clearance between the flapper bushings is a minimum of 0.004 inch (0.102 mm) at both locations, the engine bleed air 5th stage check valve at that location has passed this inspection. I knew that aviation engineering dealt with tight tolerances, but boy, it…

They've had calipers for literally thousands of years. I used to be involved in some intermediate gunsmithing work, and we had these tools called 'dial calipers' which have a little gauge you read and you can measure extremely precise things. We used it for getting cylinder diameters or clearances that needed that degree of precision. I can only imagine that in aviation, there are even more advanced tools, especially…

It's not necessary to use calipers to measure these tolerances. In this case talking about clearance between two parts you just use a feeler gauge which is a calibrated thickness of metal. If the documentation says no more than X mm, you grab your X gauge and make sure it doesn't fit. It's the same if you're working on a 737 or your John Deere.

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

#62

Post by KMag »

bilbo0s wrote: post #58
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.

couldn't get more simple than that. Believe it or not, that's actually a lot of the idea that drives commercial aviation design. Or used to anyway.

... and most engineering in general. Simple solutions tend to be very robust and often cost-effective.

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

#63

Post by nogabebop23 »

kube-system wrote: post #43
adenozine wrote: post #16

Earlier quoted context omitted.

They've had calipers for literally thousands of years. I used to be involved in some intermediate gunsmithing work, and we had these tools called 'dial calipers' which have a little gauge you read and you can measure extremely precise things. We used it for getting cylinder diameters or clearances that needed that degree of precision. I can only imagine that in aviation, there are even more advanced tools, especially…

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

yes - this is related to non-routine maintenance. I assume operation prevents moisture forming that can corrode. Storage for several weeks or months means this is like a more stringent used car "road worthiness" inspection.

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

#64

Post by tonyhb »

rlpb wrote: post #19
wwv25 wrote: post #7

One of the inspection checklist items: Measure the clearance between the flapper bushings at both locations on each engine bleed air 5th stage check valve. If the clearance between the flapper bushings is a minimum of 0.004 inch (0.102 mm) at both locations, the engine bleed air 5th stage check valve at that location has passed this inspection. I knew that aviation engineering dealt with tight tolerances, but boy, it…

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.

Yep. Also, fun fact, these are used in dentistry and orthodontics to check spaces between your teeth. We use the same information in our 3D treatment planning environment.

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

#65

Post by nemetroid »

enraged_camel wrote: post #57
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?

Explain that to the MBAs and bean-counters who are in charge over at Boeing.

The 737 Classic was introduced in 1984.

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

#66

Post by KMag »

frakt0x90 wrote: post #36
leetrout wrote: post #3

I have been wondering how dangerous flying is going to be when when / if it comes back and all these planes come out of storage. Mechanical things just sitting around is some times far worse than them being in constant use.

You still have to keep the aircraft's normal maintenance schedule even when it's in storage.

Though, if the maintenance schedule items are mostly of the form "W needs to be inspected after X flight hours, Y landings, or Z days since last inspection", there's probably significantly less experience backing up the Z parameter.

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

#67

Post by na85 »

bamboozled wrote: post #39
linuxftw wrote: post #27

Earlier quoted context omitted.

The only person here that knows what they're talking about. Everyone's talking about calipers :/

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.

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

#68

Post by perardi »

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?

I’m guessing some other parameter was more important. Thermal expansion characteristics, ease of tooling, interactions with the materials around it, resistance to some other non-oxidative chemical corrosion…

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

#69

Post by kitteh »

CaptainZapp wrote: post #24
adenozine wrote: post #16

Earlier quoted context omitted.

They've had calipers for literally thousands of years. I used to be involved in some intermediate gunsmithing work, and we had these tools called 'dial calipers' which have a little gauge you read and you can measure extremely precise things. We used it for getting cylinder diameters or clearances that needed that degree of precision. I can only imagine that in aviation, there are even more advanced tools, especially…

Boeing used to be a well respected company. At least until the merger with McDonnell Douglas, which turned it from an engineering driven company to a financial engineering company.

Eh there were several phases of stupidity there.

757 to replace the 727 when the 727 was doing quite fine. That said the 757 is a great plane and proved out well, just had a high price tag that really held it back.

The delay and screwing around with getting the 767 out there for fear it would mess with 747 sales. Let airbus get ahead with wide-bodies and took longer than expected to get the ER variants out.

Post McDonnell Dougals:

The handling of the 717 (basically shutting it down when there was demand). Could have had an impact if they wanted to bring it to the regional space (to go against the crj900+ and EMB ejets).

Oh so much in the planning and execution of the 787.

The continued extending of the 737 well beyond what it should be (see the 900, the MAX).

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

#70

Post by nabilhat »

linuxftw wrote: post #27
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.

The only person here that knows what they're talking about. Everyone's talking about calipers :/

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's office that only comes out for special occasions, like when your boss has to tell their boss to scrap a 737.
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