Posts about: "EASA" [Posts: 16 Page: 1 of 1]¶

Subjects CCTV  Dual Engine Failure  Engine Failure (All)  TOGA

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Subjects FAA  Switch Guards

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Quote:

Originally Posted by StudentInDebt

this isn\x92t the type of switch fitted to the 787 as a fuel control switch, totally irrelevant but has generated yet more nonsense. The switches are spring loaded (or so it feels) in addition to having a massive block to prevent inadvertent operation in either direction. Anyone suggesting they could be accidentally \x93knocked off\x94 is so clueless about their operation it\x92s actually painful to rebut

The type of switch being discussed is the specific type reported as being liable to problems. The SAIB is here https://ad.easa.europa.eu/blob/NM-18...SIB_NM-18-33_1 and specifies a part number for the B788 as 4TL837-3D

That's a TL series switch with 4 poles (the "4" in "4TL"), a "type D" lock (meaning locked out of centre position per the Honeywell data sheet - the "D" in "3D." This is a photo of one:


You can find the manufacturer's datasheet here: https://octopart.com/datasheet/4tl83...ywell-25749542

Problems with critical switches aren't new on 787-8s. For instance, in addition to the SAIB above, there's this AD: https://www.federalregister.gov/docu...pany-airplanes

Looking at the photo above, it isn't just wear that's potentially an issue, but foreign object impingement. There don't appear to be gaitors fitted to these switches in the 788, so the locking mechanisms are potentially susceptible to a build-up of material if not kept clean. There are a range of other failure modes possible, whilst the SAIB specifically describes found-in-the-field problems with these switches.

Yes, they're chunky, and very positive when new. That doesn't mean they shouldn't be discussed.

Subjects Air Worthiness Directives  Honeywell  Special Airworthiness Information Bulletin

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Quote:

Originally Posted by skwdenyer

The type of switch being discussed is the specific type reported as being liable to problems. The SAIB is here https://ad.easa.europa.eu/blob/NM-18...SIB_NM-18-33_1 and specifies a part number for the B788 as 4TL837-3D

That's a TL series switch with 4 poles (the "4" in "4TL"), a "type D" lock (meaning locked out of centre position per the Honeywell data sheet - the "D" in "3D." This is a photo of one:


You can find the manufacturer's datasheet here: https://octopart.com/datasheet/4tl83...ywell-25749542

Problems with critical switches aren't new on 787-8s. For instance, in addition to the SAIB above, there's this AD: https://www.federalregister.gov/docu...pany-airplanes

Looking at the photo above, it isn't just wear that's potentially an issue, but foreign object impingement. There don't appear to be gaitors fitted to these switches in the 788, so the locking mechanisms are potentially susceptible to a build-up of material if not kept clean. There are a range of other failure modes possible, whilst the SAIB specifically describes found-in-the-field problems with these switches.

Yes, they're chunky, and very positive when new. That doesn't mean they shouldn't be discussed.

This switch thing is a nothing burger. If you\x92ve ever operated these switches you\x92d know how they feel. They require a very distinct pull and are most definitely either on or off. There is no impossibly balanced in between position.

Subjects Air Worthiness Directives  Honeywell  Special Airworthiness Information Bulletin

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Subjects Engine Failure (All)  Engine Shutdown  Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches  Honeywell  SAIB NM-18-33  Special Airworthiness Information Bulletin

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Subjects Air Worthiness Directives  Fuel (All)  Fuel Cutoff Switches  Fuel Cutoff Switches (detent)  Preliminary Report

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Subjects Air Worthiness Directives  Fuel (All)  Fuel Cutoff Switches  Fuel Cutoff Switches (detent)  Preliminary Report

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Well, speaking of fuel-cut switches, I read NM-18-33 SAIB with attention, and as a not-that-fluent english speaker, I stumbled on this sentence (my bold):

Quote:

If the locking feature is disengaged , the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation.

I could hardly figure what the "disengaged" word meant in this context, so I did a Google search for the switch part numbers (especially "766AT614-3D") to figure the difference between them, and a page from this chinese web site was part of the results.

And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition":

Incorrect lock tab position on fuel cut-off switch

If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state.

The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated.

Subjects Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches  SAIB NM-18-33  Special Airworthiness Information Bulletin

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Quote:

Originally Posted by JPI33600

Well, speaking of fuel-cut switches, I read NM-18-33 SAIB with attention, and as a not-that-fluent english speaker, I stumbled on this sentence (my bold):



I could hardly figure what the "disengaged" word meant in this context, so I did a Google search for the switch part numbers (especially "766AT614-3D") to figure the difference between them, and a page from this chinese web site was part of the results.

And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition":

Incorrect lock tab position on fuel cut-off switch

If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state.

The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated.

NM-18-33 SAIB left me wondering the same thing. It give a procedure for detecting the defect but omits to explain the cause. I was thinking that the wrong switches had been supplied/fitted. Assuming the image from the Chinese web site is correct, it is disappointing that the actuator can get into that state. I did not see anything that said whether that was how the switch arrived from Honeywell or if there was a defect that allowed the actuator to turn.

One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea.

Subjects Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches  Honeywell  SAIB NM-18-33  Special Airworthiness Information Bulletin

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Quote:

Originally Posted by DTA

NM-18-33 SAIB left me wondering the same thing. It give a procedure for detecting the defect but omits to explain the cause. I was thinking that the wrong switches had been supplied/fitted. Assuming the image from the Chinese web site is correct, it is disappointing that the actuator can get into that state. I did not see anything that said whether that was how the switch arrived from Honeywell or if there was a defect that allowed the actuator to turn.

One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea.

Why are you wasting your own time?

If any of that were true why would it happen after Vr and why would one pilot ask: \x93why did you go to cutoff\x94. That is an observed deliberate action. Cmon folks enough with the nonsense!

Why are people shying around the truth!?

Subjects Honeywell  SAIB NM-18-33  Special Airworthiness Information Bulletin

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Subjects Honeywell  SAIB NM-18-33  Special Airworthiness Information Bulletin

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Subjects FAA  Fuel (All)  Fuel Cutoff Switches  SAIB NM-18-33  Special Airworthiness Information Bulletin

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Subjects FAA  Special Airworthiness Information Bulletin

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Subjects Special Airworthiness Information Bulletin

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Subjects FAA  RUN/CUTOFF  Special Airworthiness Information Bulletin

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