FAA EAD for non-MAX 737s - engine failures
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FAA EAD for non-MAX 737s - engine failures
WASHINGTON — The Federal Aviation Administration (FAA) on Friday issued an emergency airworthiness directive for 2,000 U.S.-registered Boeing 737 NG and Classic aircraft that have been in storage, warning they could have corrosion that could lead to a dual-engine failure.
https://rgl.faa.gov/Regulatory_and_G..._Emergency.pdf
https://rgl.faa.gov/Regulatory_and_G..._Emergency.pdf
FAA EAD for non-MAX 737s - engine failures
The FAA has issued an Emergency Airworthiness Directive for 737-300 to -900ER aircraft that have been stored or in limited use:
The nut: possible corrosion and sticking of 5th-stage compressor bleed-air check valves due to lack of use. May cause unrecoverable compressor stalls on power reduction (e.g. TOD) and off-airport landings if both engines are affected.
https://www.documentcloud.org/docume...-for-737s.html
The nut: possible corrosion and sticking of 5th-stage compressor bleed-air check valves due to lack of use. May cause unrecoverable compressor stalls on power reduction (e.g. TOD) and off-airport landings if both engines are affected.
https://www.documentcloud.org/docume...-for-737s.html
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That youtube video has some inaccurate and confusing information. Any system or feature that bleeds air off the engine is an "engine bleed air" system or feature. There are stability bleed ports and valves, and there are aircraft service bleed ports and valves. The system affected by the AD is the aircraft service bleed air that comes from the engine from either the 9th stage or 5th stage of the HP compressor, depending on the source pressure. It's the system that feeds the air conditioning packs (pressurizing the airplane) and the wing anti-ice system. It is not an engine stability bleed or starting bleed valve. The 5th stage check valve on the affected airplanes is not spring-closed. It normally moves to the closed position due to gravity and air flow/pressure. When the check valve sticks open it's not the 5th through 9th stages that stall - it's the stages downstream of that area that stall initially, leading to compressor flow reversal (the "bangs" you hear about in the reports).
But yes, if it sticks open you will almost always end up with a shutdown, and if it sticks on both engines it's likely to be a forced landing. The AD was issued because the first few flights after a storage period have a risk of dual engine shutdown that is quite high.
But yes, if it sticks open you will almost always end up with a shutdown, and if it sticks on both engines it's likely to be a forced landing. The AD was issued because the first few flights after a storage period have a risk of dual engine shutdown that is quite high.
But yes, if it sticks open you will almost always end up with a shutdown, and if it sticks on both engines it's likely to be a forced landing. The AD was issued because the first few flights after a storage period have a risk of dual engine shutdown that is quite high.
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But yes, if it sticks open you will almost always end up with a shutdown, and if it sticks on both engines it's likely to be a forced landing. The AD was issued because the first few flights after a storage period have a risk of dual engine shutdown that is quite high.
EDIT: now been pointed out, thanks, that I missed the reports of multiple single-engine events being the trigger, as noted in the AD. Must RTFAD slowly and carefully before posting, not skim read :-)
Last edited by infrequentflyer789; 27th Jul 2020 at 22:15.
FYI: I believe there were 4 separate inflight single engine decels during letdown. The EAD was issued as there was a possibility that both engines could decel at the same time. There's an FAA doc out there and will post if I can find it.
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Dave, do you know why this is 737 specific and doesn't apply to the CFM powered A320? That check valve is usually considered part of the engine and I'd expect if they used the same valve on both the CFM56-3 and -7, I would have expected them to use the valve on the CFM56-5 on the A320.
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How did the AD come to be issued though? Is the stuck valve a known risk that was previously thought to be acceptable because 737s were not usually parked up for months, or has there actually been an incident due to this (maybe only on one engine)? Engines need to be regularly run-up on parked aircraft - is that enough to trip this failure mode, has it happened on the ground perhaps?
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Benjamin
Ah, got it, thanks (and to others who have pointed it out). I figured single engine events with probability of dual event would be the trigger, but must have missed the reports on first read of the AD.
Ah, got it, thanks (and to others who have pointed it out). I figured single engine events with probability of dual event would be the trigger, but must have missed the reports on first read of the AD.
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which airplanes
Hi, is the info out which airplanes had the 4 shutdowns ? I mean, were they parked near the ocean, in realtively salty, corrosion-prone air, before getting usee again ?
Thanks
Thanks
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The valve in the video is a different part number valve from a different manufacturer. He says it has a spring, and it appears to be sticky. The valve on the 737s in question is a Honeywell valve, not Dunlop.
I heard today that Airbus uses a different valve from a different vendor on the CFM56-5 installations.
I heard today that Airbus uses a different valve from a different vendor on the CFM56-5 installations.
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Pretty much no suitable metal is safe forever around salt and water. Stainless steel is a marketing term. The technical term is corrosion resistant steel and the more resistant versions tend to gall in contact with similar or identical alloys. Aluminum parts requires surface treatments to protect them but damage to that surface treatment can leave the aluminum open to corrosion; I would guess that there are bits of grit in the air stream that would blast those surface treatments off eventually. Aluminum also expands more with temp than steels do, which would contribute to the next problem.
One problem in making these valves is that if the flaps have clearance in the hinges they will rattle and rub and wear against the hinge pin in the very high-frequency vibration environment, so the gaps need to be very small. But with small gaps any corrosion at all can bridge the gap and bind the hinge. In normal use any corrosion will be at some small location and operation will wear it down as if forms. Sitting stationary does not cause this wear. Unlike most locations this one cannot be lubricated; oil would be blown off and grease, which consists of oil+ thickener, would see depletion of the oil leaving the thickener to bind up the mechanism.
One problem in making these valves is that if the flaps have clearance in the hinges they will rattle and rub and wear against the hinge pin in the very high-frequency vibration environment, so the gaps need to be very small. But with small gaps any corrosion at all can bridge the gap and bind the hinge. In normal use any corrosion will be at some small location and operation will wear it down as if forms. Sitting stationary does not cause this wear. Unlike most locations this one cannot be lubricated; oil would be blown off and grease, which consists of oil+ thickener, would see depletion of the oil leaving the thickener to bind up the mechanism.
I hadn't heard that the sticky problem was deterioration of the metal (happy to hear if so) I was assuming the problem was foreign material coming out of solution and gumming up the valves when the engines were left not running for long periods of time
