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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

#141

Post by FabHK »

esaym wrote: post #123
Sebb767 wrote: post #25

Earlier quoted context omitted.

I think it would be rather hard to land a plane off the airport without substantial damage, especially when talking about larger ones.

Indeed, but planes are quite repairable. I don't have a source for this (too lazy to look), but I briefly worked for boeing on a government contract to service C-17 aircraft for the air force. There was a story there of a C-17 landing on a dirt/sand field somewhere in the middle east (this is normal there) except in this case there was a small concrete barrier out in the middle of the field that wasn't seen. The fron…

> planes are quite repairable

The Qantas A380 from Singapore to Sidney that had an uncontained engine failure was repaired and entered service again, at an estimated cost of about $150m, or about 1/3 of the price of a new one.

https://en.wikipedia.org/wiki/Qantas_Flight_32

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

#142

Post by FabHK »

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.

I wonder what effect will dominate:

1. BAD: The degradation of airplanes in storage (seems that's fairly well understood, though)

2. BAD: The loss of proficiency and currency by the crews

3. GOOD (maybe?): Less traffic?

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

#143

Post by inamberclad »

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…

One of the first things I learned in my college shop class was how to mill a piece of metal to within a few thou of the target dimension.

For this kind of measurement, they could almost certainly just use a feeler gauge and make sure that the 4 thou gauge fits.

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

#144

Post by noir_lord »

cartoonfoxes wrote: post #81
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.

They're deceptively simple. If you want to get into the history of modern manufacturing, a lot can be written about the development of gauges of accurately known dimensions.

Somewhat sadly a lot of the drive for that tolerance was weapons, until we could accurately make very high tolerance (for the day) parts you couldn't use parts from one rifle on another without a smith, it certainly wasn't field serviceable - this imposed a lot of maintenance overhead until they solved it properly.

It seems like we really like to push the limits when it comes to shooting each other.

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

#145

Post by noir_lord »

KMag wrote: post #62
bilbo0s wrote: post #58

Earlier quoted context omitted.

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.

and easier to troubleshoot/replace.

> A complex system that works is invariably found to have evolved from a simple system that worked. A complex system designed from scratch never works and cannot be patched up to make it work. You have to start over, beginning with a working simple system. - John Gall

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

#146

Post by Animats »

BinaryRage wrote: post #137
Animats wrote: post #125

Earlier quoted context omitted.

Adjustments to tolerance are something aviation still has, but which has disappeared from consumer products. It's too labor-intensive. Here's the "Adjustments" manual for a Model 15 Teletype, the 1930-1958 model. I've restored two of those. Making those adjustments isn't that difficult, just time-consuming. Adjustment to 0.002 in. is sometimes required, but it's not that hard. Most Teletype adjustments can be set wit…

I was staggered by how much adjustment was required when watching CuriousMarc's excellent Model 19 restoration series, seems incredibly finicky. https://www.youtube.com/watch?v=_NuvwndwYSY&list=PL-_93BVApb...

I just put up a few stills of my own restorations, some short demo videos, and Github repositories for the interface board and the software. I had no idea anyone would want to watch four hours of Teletype repair videos.

Model 15 and 19 Teletypes are not hard to work on. Everything comes apart easily; it's all screws and lockwashers. They're human scale; it's not like building surface mount electronics or repairing an iPhone, where you work under a microscope. The adjustments aren't that finicky, except for a few near the selector magnet. It also helps that the whole thing is unidirectional - there's a straightforward path from input signal to typebar hitting the paper, and you can work through problems in order. As a nice feature, movement is powered in one direction and spring-loaded in the other, so if something gets stuck, it's just stuck in the operated position and doesn't get bent or broken.

Aircraft are built like that. Some parts require careful adjustment, but there's almost always an easy way to check that you got it right. Because, after all, you can't fix it in flight.

Mechanical design has a design philosophy embedded in it. If you work on complex mechanical systems, you can sometimes get a feel for how the original designer thought. Good machinery design is not a common skill. All the good Teletypes were designed by only two people - Howard Krum and Ed Kleinschmidt.

Very few people study this any more in the US, which hurts when you need to design production machinery.

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

#147

Post by madengr »

bluGill wrote: post #112
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.

I thought it corrodes if scratched and left submerged, like rust spots on utensils in the dishwasher. Something about the chromium not having the proper environment to form an oxide layer, before the iron.

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

#148

Post by meristem »

Aircraft are meant to be in high usage, so decreased flight time and larger flight intervals will cause interesting problems. For example many part 135 planes currently parked need to be rolled to a different position daily because parked weight deforms tyres.

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

#149

Post by linuxftw »

noir_lord wrote: post #144
cartoonfoxes wrote: post #81

Earlier quoted context omitted.

They're deceptively simple. If you want to get into the history of modern manufacturing, a lot can be written about the development of gauges of accurately known dimensions.

Somewhat sadly a lot of the drive for that tolerance was weapons, until we could accurately make very high tolerance (for the day) parts you couldn't use parts from one rifle on another without a smith, it certainly wasn't field serviceable - this imposed a lot of maintenance overhead until they solved it properly. It seems like we really like to push the limits when it comes to shooting each other.

> Somewhat sadly

Weapons can be used for defensive purposes. There's nothing inherently wrong with them, only how people use them.

> parts you couldn't use parts from one rifle on another without a smith

You cannot swap bolts in the field on most rifles. At minimum, you require a go/no go gauge. The tolerances on modern firearms are very precise.

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

#150

Post by aunty_helen »

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…

>The difference between traceable and ordinary measurement equipment is a couple of extra $.

This idea again. I don't know why people are saying this. It's not true. Aviation you're allowed to use any tool you want unless the workshop manual says to use a specific tool.

OEM calibration certs are useless to an aviation company because it's someone else promising accuracy that could see you thrown in jail if it's wrong. Before tooling is used the first time it will be calibrated. Then calibrated again at set intervals.

>hex torque drivers with cal stickers

It's most likely the part had stickers so it was in their system for visual inspection for good condition. I have a pair of lockwire pliers that were pulled from the shop floor due to them being indicated worn during a visual inspection. I still have them 7 years later and they're still the sharpest pliers I own.

As for the traceability from birth, this applies to parts that go on the aircraft not tooling. Tooling traceability you need to know what tool was used if it's required to be calibrated. ie torque wrenches.

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