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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

#121

Post by esaym »

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…

>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 3/32" (#40 drill bit), then up drill it to .242 (C drill bit), then swap out to a .242 to .247 "reamer" and ream the hole to .247. The hilok itself is around .248-.249" so you can't just "push" it in but tap it in with a hammer or rivet gun. There was a "go-no-go" gauge. The "go" end was .246 and the "no go" end was .248. So yes, tolerances of 0.001" are quite common.

[0] https://duckduckgo.com/?q=hilok&ia=web

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

#122

Post by kenny11 »

jschwartzi wrote: post #17
raverbashing wrote: post #8

That is surprising. Pandemic or no pandemic, you have NGs and classics going and coming out of storage with a certain frequency. Funny this wasn't found before.

I think it wasn’t an issue before because most airlines aren’t going to keep a plane they have in storage for multiple days. They’ll sell it to another airline. Otherwise they still have to maintain it and pay storage fees plus whatever lease or finance costs are associated with the plane. Boeing runs a finance corporation which is how a lot of planes are “sold.” They have to plan for maintenance windows and unexpect…

This is also why planes out of use for extended periods are typically stored in dry, desert climates - less moisture in the air to cause corrosion.

The massive increase in stored aircraft due to the pandemic meant that there wasn't enough room at these airports, and so aircraft had to be stored anywhere there was space available, often in less than ideal climates.

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

#123

Post by esaym »

Sebb767 wrote: post #25
rileyteige wrote: post #5

Earlier quoted context omitted.

Not necessarily. A "forced off-airport landing" could also be the result of an engine failure beyond gliding distance of an airport. Or engine fire, medical emergency in remote area, etc. There are many emergencies that could force an aircraft to the ground, off-field. Not all off-field landings result in an accident, or "crash". From our own regulations, NTSB 830 "NOTIFICATION AND REPORTING OF AIRCRAFT ACCIDENTS..."…

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 front nose gear impacted the barrier and it torn the nose gear off along with a large chunk of the underside of the fuselage. As the front of the plane touched the ground, the hole scooped up sand and blasted a ton of it into the cargo bay. A crew was flown out there and they "fixed" it and it was flown back to the states.

Another popular instance was the Lockheed EP-3 flying the China coast in 2001 before impacting a Chinese fighter in the air and making a forced "rough" landing. It was taken apart and shipped back to the states where it was repaired in Waco Texas and continues to patrol the China coast to this day.

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

#124

Post by [deleted] »

numpad0 wrote: post #59
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.

With that in mind the phrasing sound to me like “the bushing is supposed to be moving freely, if it’s stuck to the surface you have to replace it” in aviation lingo without using ambiguous words like “freely”

[deleted]

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

#125

Post by Animats »

esaym wrote: post #121
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…

>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 with feeler gauges. You don't need a micrometer.

[1] http://aetherltd.com/public/model15manuals/138_Model15_Adj_O...

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

#126

Post by SAI_Peregrinus »

ryandrake wrote: post #120
kube-system wrote: post #99

Earlier quoted context omitted.

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.

You can take just about any measuring tool to a calibration company and get the certificate. Indeed, you MUST do this on a regular basis: calibration is a set of measurements of a system over time. Single-point-in-time calibration is worthless for showing drift. You can also get things tested at a range of temperature and humidity levels, high-grade lab standards may get calibrated at multiple temperature & humidity levels every 6 months.

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

#127

Post by wjdoge »

formerly_proven wrote: post #110
myself248 wrote: post #96

Earlier quoted context omitted.

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…

There's a "high tech" (i.e. they mostly don't use cutting tools) machining shop nearby; their proprietary machines (designed & built in-house, never sold or leased externally, only used for contract manufacturing) are repeatable within a few µm (they offer tolerancing below 5 µm on finished parts) and move about as quick as the rapid traverse on a more standard CNC milling machine.

EDM?

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

#128

Post by SAI_Peregrinus »

formerly_proven wrote: post #110
myself248 wrote: post #96

Earlier quoted context omitted.

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…

There's a "high tech" (i.e. they mostly don't use cutting tools) machining shop nearby; their proprietary machines (designed & built in-house, never sold or leased externally, only used for contract manufacturing) are repeatable within a few µm (they offer tolerancing below 5 µm on finished parts) and move about as quick as the rapid traverse on a more standard CNC milling machine.

Nanotech Systems (Moore's current name) make a high-precision drum lathe with 1nm positioning precision, with a 2600mm working area [1].

1 part in 2,600,000,000.

Dan Gelbart built his own lathe with Within a few thousandths of an inch isn't very impressive. I can hold 1 thou on a cheap manual lathe (Grizzly G0602 10"x22" working area), with a decent amount of care. Holding to tenths (1/10000") is impossible with the equipment I can afford though.

[1] https://nanotechsys.com/wp-content/uploads/2019/12/HDL2600-B... [2] https://www.youtube.com/watch?v=sFrVdoOhu1Q

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

#129

Post by formerly_proven »

SAI_Peregrinus wrote: post #128
formerly_proven wrote: post #110

Earlier quoted context omitted.

There's a "high tech" (i.e. they mostly don't use cutting tools) machining shop nearby; their proprietary machines (designed & built in-house, never sold or leased externally, only used for contract manufacturing) are repeatable within a few µm (they offer tolerancing below 5 µm on finished parts) and move about as quick as the rapid traverse on a more standard CNC milling machine.

Nanotech Systems (Moore's current name) make a high-precision drum lathe with 1nm positioning precision, with a 2600mm working area [1]. 1 part in 2,600,000,000. Dan Gelbart built his own lathe with Within a few thousandths of an inch isn't very impressive. I can hold 1 thou on a cheap manual lathe (Grizzly G0602 10"x22" working area), with a decent amount of care. Holding to tenths (1/10000") is impossible with the…

That's resolution, not precision or repeatability, although such high resolution is very impressive. I'm not sure how exactly a glass scale is supposed to work to 34 pm, I assume these use analog interpolation between marks or perhaps some kind of interference mechanism.

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

#130

Post by formerly_proven »

wjdoge wrote: post #127
formerly_proven wrote: post #110

Earlier quoted context omitted.

There's a "high tech" (i.e. they mostly don't use cutting tools) machining shop nearby; their proprietary machines (designed & built in-house, never sold or leased externally, only used for contract manufacturing) are repeatable within a few µm (they offer tolerancing below 5 µm on finished parts) and move about as quick as the rapid traverse on a more standard CNC milling machine.

EDM?

Laser
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