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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

#131

Post by doodlebugging »

bluGill wrote: post #109
doodlebugging wrote: post #97

Earlier quoted context omitted.

This is why I still own most of the vehicles I've purchased over the last 30 years. It is much cheaper to replace worn parts, ideally before they fail, than it is to replace the entire vehicle. I have the skillsets needed to maintain my own equipment and the tools so I just monitor the operating condition of each and replace or repair things as needed. These planes have regular maintenance checks and diagnostics to h…

Airplanes worry about fatigue. They have to be replaced after so many years or the wings will fall off in the air. If the airplane is only a few weeks away from replacement when it fails an inspection you scrap it now, if it has years to go you replace parts.

I don't disagree with this at all. That is how it should work and that is apparently how it is working.

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

#132

Post by jacquesm »

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…

Thousandths of an inch is not quite as precise as 100ths of a mm though they are at the same order of magnitude and top machinists using temperature corrections and all kinds of trickery can do better than that. Reproducibly.

Measuring with such high degrees of precision is easier than manufacturing by a very large margin. There are calibrated standards that fit in your pocket quite easily. Even ye olde feeler gauge was pretty precise if you were careful with it.

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

#133

Post by jacquesm »

Anything mechanical that you don't use is on the way out, airplanes, cars it doesn't matter. Use it or lose it very much applies and all it takes is to not use something for a while to find completely new failure modes. Case in point, and very timely: just today I had to replace the valve that allows for the pressurization of the fuel tank on my car simply because it wasn't used for three months. It had seized and no amount of brake fluid or other solvents would get rid of the gunk enough to unstuck the valve so it could be worked.

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

#134

Post by aunty_helen »

myself248 wrote: post #96
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…

4 thou isn't a particularly high degree of precision. For about five bucks you can get feeler gauges more accurate than that, and for about thirty you can get a micrometer that's accurate to 0.0005" over a whole inch. (I checked mine against a set of grade 2 gauge blocks at their calibrated temperature.) Normal CNC machines, not designed for extreme precision but the sort of thing an exceptionally serious hobbyist or…

The most accurate measuring device at the jet engine MRO I worked at was a CMM. It had an accuracy of 2 micron, 0.00008"

It was a robotic arm that lived in a temperature controlled room. The parts it was to measure were left inside the room to acclimatise. When they were at the correct temperature, you would put a part on the largest granite block in the southern hemisphere that was so flat they used lasers to calibrate it. Then run the program for the part. The arm would move into position and then a little probe would touch the part to get a measurement. It was used to measure things like warpage of inner diameters etc.

Funny trivial, if you ran the wrong program the arm would end up colliding with the part causing the probe to break. There was always spare probes kept because this happened. $20k each.

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

#135

Post by elliottkember »

0xffff2 wrote: post #89
FDSGSG wrote: post #42

Earlier quoted context omitted.

> I rather doubt there are any examples of an off airport landing of a 737 without significant damage to the aircraft. https://en.wikipedia.org/wiki/TACA_Flight_110

Well, I stand corrected. That's both surprising and an incredible feat of airmanship by the pilots! Since I love reading about these kinds of incidents and the best way to solve a problem is to claim it's impossible, I amend my claim to "I rather doubt there are two examples of an off airport landing of a 737 without significant damage to the aircraft." :)

The famous Gimli Glider wasn't badly damaged either, although it was a 767!

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

#136

Post by gonzo »

olyjohn wrote: post #76
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.

I use these on my car to check / adjust valve clearances. Every 30,000 miles.

You have a fantastic engine.

When I was young, it was guaranteed that a lifter would let loose just before you picked up your date on Saturday night if you had not “run the valves” in the past month.

Clack-clack-clack-clack-...

Date: Why does your car sound like it’s broken?

Me:

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

#137

Post by BinaryRage »

Animats wrote: post #125
esaym wrote: post #121

Earlier quoted context omitted.

>Do field technicians have dependable tools and methods of measuring with such high degrees of precision? Yes, it is basic stuff in most mechanics. For instance, the valve clearance on most car engines is going to be .002-.005. I worked aviation maintenance for years. Most larger planes are held together with 'hiloks' [0] They are an "interference" fit. For a quarter inch hilok, you'd first pilot drill a hole around…

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...

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

#138

Post by gonzo »

bluGill wrote: post #109
doodlebugging wrote: post #97

Earlier quoted context omitted.

This is why I still own most of the vehicles I've purchased over the last 30 years. It is much cheaper to replace worn parts, ideally before they fail, than it is to replace the entire vehicle. I have the skillsets needed to maintain my own equipment and the tools so I just monitor the operating condition of each and replace or repair things as needed. These planes have regular maintenance checks and diagnostics to h…

Airplanes worry about fatigue. They have to be replaced after so many years or the wings will fall off in the air. If the airplane is only a few weeks away from replacement when it fails an inspection you scrap it now, if it has years to go you replace parts.

It’s not years, it’s “cycles” take-off/landing with pressurized passenger compartment in-between.

And it’s not often the wings fall off, but the tail does, or sometimes a huge hole opens in the “skin” of the airframe.

Example: Aloha Airlines Flight 243

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

#139

Post by FabHK »

benrrio wrote: post #2

The official PDF document is here: https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf... I always wondered what the proper terms was for an airplane crash, and now I know: "forced off-airport landing"

And you know the checklist for forced off-airport landings at night?

1. Airspeed - SET

2. Fuel Valve - OFF

3. At 100 ft: Landing Lights - ON

4. If you don't like what you see: Landing Lights - OFF

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