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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

#71

Post by jrockway »

WrtCdEvrydy wrote: post #56
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.

If you're into 3D Printing, feeler gauges are also a great way to level your bed... move the extruder 0.04 above the bed at four points, stick your 0.04 feeler under it and adjust the springs until it touches the feeler. Voila, one perfectly leveled 3D printer bed.

Most people use a sheet of paper for this. I wouldn't use it to check the tolerances of an airplane part, but it gets you 99% of the way there.

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

#72

Post by kube-system »

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?

I believe there are procedures/checklists for placing aircraft in and out of storage which are different than those used for normal operation, because the conditions are different. It is my understanding that this directive is an additional check that would be performed during the typical storage procedures.

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

#73

Post by elliekelly »

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.

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?

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

#74

Post by refurb »

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?

They are typically harden steel, so wear minimally and when you test a gap, you’re not really applying much force.

If the feeler gauge doesn’t slip in with minimal force, then that tells you the gaps is smaller than the gauge.

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

#75

Post by tjohns »

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.

There are manufacturer approved procedures for putting aircraft into long-term storage, as well as returning them back to service.

Yes, there is absolutely additional wear that happens just from sitting around. Repairing this (if necessary) is part of the return-to-service procedure.

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

#76

Post by olyjohn »

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.

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

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

#77

Post by bronson »

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 theory, yes. In practice, they get dirty and bent faster than they wear out.

They're cheap. Shops that care have them on a replacement schedule.

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

#78

Post by ponker »

KMag wrote: post #66
frakt0x90 wrote: post #36

Earlier quoted context omitted.

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.

There are three guidelines. Some are per flight, some are per operating hour, and some are per calendar time.

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

#79

Post by xnyan »

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?

Can’t answer for aviation but I worked in the general testing and certification industry (Underwriters Laboratories) with tons of rules and externally audited standards about calibration of measurement and test equipment.

Yes, things like rulers and gauges are tested. The schedule depends on the use case and frequency of use. For relatively light lab duty stuff, rulers and gauges were checked 1-2 times a year. Things that are used more frequency or more aggressively are checked more often.

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

#80

Post by cartoonfoxes »

nabilhat wrote: post #70
linuxftw wrote: post #27

Earlier quoted context omitted.

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…

I see this in my own shop. Digital displays instill people with greater confidence in the measurement than is warranted. This is something of a UI fail, as the tool manufacturer (Mitutoyo) has very clearly defined measurement precision for all their metrology equipment (+- 0.001" and 0.0015" for the calipers).
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