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AZORMP
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FAA EAD - CFM-56-7 and -3

Fri Jul 24, 2020 3:05 pm

Apologies if there’s a thread already.

Another strike for Boeing....the FAA issued an EAD affecting all B737 variants between the -300 and the -900ER for an issue with the Bleed Air 5th Stage Check Valve that may cause an unrecoverable compressor stall and loss of the engine. Apparently this was discovered on numerous frames that had recently returned from service.

Link: https://rgl.faa.gov/Regulatory_and_Guid ... rgency.pdf
 
Wacker1000
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 3:23 pm

They should out the operator(s) that experienced the IFSDs and go after them for improper long term storage practices.
 
CriticalPoint
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 3:26 pm

Wacker1000 wrote:
They should out the operator(s) that experienced the IFSDs and go after them for improper long term storage practices.


Pretty sure improper storage techniques have nothing to do with this.......corrosion happens anywhere and everywhere.
 
kiowa
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 5:17 pm

"another strike for Boeing" perhaps but more like Another Strike against the 737.
 
Dalmd88
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 5:49 pm

I've heard this has been found by numerous operators that stored these planes for the pandemic. This system has been problematic since day one on the NG. The failure rate on the entire engine bleed system has had many upgrades.

When I worked line mtc we were told only do the scheduled check on one airplane per night. Make sure we have all the components in stock before we started the test.The failure rate was that high. We always ended up changing one of the three main components. These were planes that we having no known issues inservice, but once you looked closely at the operation of the valves something was usually out of spec.
 
Wacker1000
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 5:50 pm

CriticalPoint wrote:
.......corrosion happens anywhere and everywhere.


That is literally the reason why there are long term storage and preservation procedures. Unless the engine OEM totally botched the procedures (highly doubtful), odds are the operator(s) didn't do the entire preservation task (it isn't a 5 minute job and you have to do it twice per airframe), didn't do a good job sealing the engines or keeping them sealed, and/or didn't bother to monitor and change the desiccant often enough.

Engines are regularly stored for months at a time in all sorts of environments and if they are treated properly they don't have issues due to corrosion when they are put into service.
 
Patroni1
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 6:00 pm

The engine Is made by CFM.
 
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lightsaber
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 6:11 pm

There is a good chance corrosion started in service. I have designed bleed air valves, they are tricky. There is often stress corrosion under certain opperating conditions.

Now, I am not that familiar with the material differences between the -5 (A320 engine) vs. -7 (NG engine). IIRC, there is more pressure and thus more heat on the -7. This probably means either a material change or the heat was just enough to make the material more susceptible to corrosion.

Lightsaber
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DlTechops
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 6:15 pm

Dalmd88 wrote:
I've heard this has been found by numerous operators that stored these planes for the pandemic. This system has been problematic since day one on the NG. The failure rate on the entire engine bleed system has had many upgrades.

When I worked line mtc we were told only do the scheduled check on one airplane per night. Make sure we have all the components in stock before we started the test.The failure rate was that high. We always ended up changing one of the three main components. These were planes that we having no known issues inservice, but once you looked closely at the operation of the valves something was usually out of spec.



I dont know when you left the line but its still the same... all parts in hand or it gets the boot.
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durangomac
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 6:48 pm

I take this EAD this way, when was the last time we have see this many aircraft put into short term storage. I suspect that under normal times the number of short term storage of aircraft was a very small number that were either going into heavy maintenance or just came out of heavy maintenance. We are probably seeing something that is usually not a problem when an aircraft just comes out of heavy maintenance or isn't seen as an issue because the part is usually replaced during heavy maintenance. All this EAD says to me is the circumstances have shown an issue with a part that becomes an issue after storage and either the process to put an aircraft in short term storage needs to be adjusted because of new findings or those prepping the planes for short term storage are doing it incorrectly.
 
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NameOmitted
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 10:48 pm

lightsaber wrote:
There is often stress corrosion under certain opperating conditions.


My understanding of corrosion is that it is a electrochemical process of oxidation of metals. My understanding of stress is that it generally refers to physically wearing down parts, often at joints or load transfer points. My understanding of both is limited, so please be kind, but what is stress corrosion?
 
Antarius
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Re: FAA EAD - B737 NG Engine Failure

Fri Jul 24, 2020 10:56 pm

NameOmitted wrote:
lightsaber wrote:
There is often stress corrosion under certain opperating conditions.


My understanding of corrosion is that it is a electrochemical process of oxidation of metals. My understanding of stress is that it generally refers to physically wearing down parts, often at joints or load transfer points. My understanding of both is limited, so please be kind, but what is stress corrosion?


Stress corrosion is basically as the name says, it occurs/requires both stress and environmental issues that cause the corrosion.

For example, steel can be under stress and function normally as it is within the metals tensile strength. However, exposing this same steel to chlorides weakens the steel and combined with the stress that it is on, causes Stress Corrosion Cracking.
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atcsundevil
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Re: FAA EAD - CFM-56-7 and -3

Fri Jul 24, 2020 11:16 pm

Please keep the thread on topic.

✈️ atcsundevil
 
WkndWanderer
Posts: 287
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Re: FAA EAD - CFM-56-7 and -3

Sat Jul 25, 2020 2:50 am

What is unique to these two versions of the CFM56 to explain why this doesn’t effect the other variants of the engine including the 5?
 
milhaus
Posts: 39
Joined: Fri Dec 10, 2010 4:19 pm

Re: FAA EAD - CFM-56-7 and -3

Sat Jul 25, 2020 6:27 am

I think that AD for other cfm56 versions will follow, those check valves are very similar.

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