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Old 21st Mar 2017, 03:44   #861 (permalink)
 
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Would a windmilling engine at cruise (i.e. shut down) still produce some degree of hydraulic pressure and electrical generation? What sort of speed would the engine be rotating at compared to idle? Or does a complete shutdown isolate everything? Just trying to understand what is to be gained by leaving a sick engine running at idle for hours. Apologies if it's a daft question...
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Old 21st Mar 2017, 08:30   #862 (permalink)
 
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Originally Posted by Octane View Post
Just trying to understand what is to be gained by leaving a sick engine running at idle for hours. Apologies if it's a daft question...

On a general point one consideration certainly on a twin is if the "sick" engine is still capable in extremis of producing useable thrust if needed then it might be sensible to leave it running......as long as procedures don't say otherwise.

However in the context of this incident they had more than a slightly "sick" engine...certainly as I read the report if the crew had gone through the Fuel Disagree checklist fully and correctly they would have been led onwards into actioning the Fuel Leak checklist, at which point they hopefully would have realised that the engine was more than just slightly "sick". The QRH would have been telling the crew they had an engine Fuel Leak and that they needed to shut it down, not leave it at idle...but for reasons various they never got as far as the Fuel Leak checklist (see my previous comment about the 777 checklist).

Last edited by wiggy; 21st Mar 2017 at 11:36.
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Old 21st Mar 2017, 09:13   #863 (permalink)
 
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Thanks Wiggy,
What about the first part of my question?
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Old 21st Mar 2017, 09:18   #864 (permalink)
 
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TBH I'd be sticking my neck out offering up numbers since I haven't seen a real windmilling engine in a long long time and never on a real 777. Might be one for those who do or who involved in airtests to answer.

Last edited by wiggy; 21st Mar 2017 at 11:35.
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Old 21st Mar 2017, 22:01   #865 (permalink)
 
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Quote:
Would a windmilling engine at cruise (i.e. shut down) still produce some degree of hydraulic pressure and electrical generation? What sort of speed would the engine be rotating at compared to idle?
A windmilling engine can produce some hydraulic pressure - in fact some aircraft can get away without a RAT because in an all-engine out condition there is sufficient hydraulic pressure from the windmilling engines to allow basic aircraft control (the 747-400 (and earlier 747 models) fall into this category - however the 747-8 needs a RAT). However the GE90 on the 777 does not produce much hydraulic pressure when windmilling (big fan, little core means relatively low N2 windmill speeds) - hence the 777 needs a RAT. Some newer installations (e.g. the GEnx) actually disconnect the hydraulic pump for an engine shut-down in flight to increase the windmill N2 sufficiently to make a windmill re-start physically possible.
There is no meaningful electrical generation on most windmilling engines - once N2 (N3) drops below 50%, the IDG drive disconnects.
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Old 22nd Mar 2017, 02:19   #866 (permalink)
 
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Hi td,

Thanks for the detailed response to my question. Curiosity satisfied, much appreciated.

Related to this thread, I sent this to my brother a while back. (He's the real pilot, I'm the armchair pilot as you may have gathered)

"If those guys were driving their car home from work and the instruments were giving odd indications, the engine started vibrating and producing fumes I'm sure they'd pull over and turn the thing off 100% of the time. Wouldn't they? I doubt they'd keep driving home hoping she'll be right mate...?!" Am I being a bit harsh?

Bro hasn't replied, he's a bit busy. In the middle of a B777 endorsement ironically! :-)
Loads of SIM work of course but he says the 777 is easier to fly than the 737. One thing I found a bit astonishing, he has yet to see/ touch/ feel/ kick the tyres of a real 777 aircraft. The 1st time he gets to, is when he flies one to LA!


That's why I thought I'd ask you gentleman/ ladies all those questions..
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Old 22nd Mar 2017, 08:18   #867 (permalink)
 
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Thanks tdracer, interesting stuff.

Octane:

Quote:
Originally Posted by Octane View Post
"If those guys were driving their car home from work and the instruments were giving odd indications, the engine started vibrating and producing fumes I'm sure they'd pull over and turn the thing off 100% of the time. Wouldn't they? I doubt they'd keep driving home hoping she'll be right mate...?!" Am I being a bit harsh?
Fair point, but companies these days don't like folks going off piste (especially on a twin) and shutting engines down if it is not a QRH requirement or a catastrophic problem outside the scope of the QRH.

Just out of interest if your brother has time ( though I'm guessing he won"t) ask him to have a look at the report and the 777 QRH, look at the early symptoms of engine issues on the SQ flight and see which relevant checklist has a requirement to shut the miss behaving engine down. FWIW the crew hadn't had a low oil pressure or high oil temp EICAS warning, the vibrations don't add up to being severe and were the flight crew really aware how severe was the fumes smell was in the cabin?

Ultimately it seems the crew thought they in conjunction with the company engineers on satcom had solved or at least contained the problem and hadn't had to shut the engine down.....I suspect the real "**** me " moment might have occurred quite quickly thereafter if they had run the Fuel disagree/Leak checklists properly though the one engine at idle would have might have delayed diagnosis (sorry to bring that up again but TBF it is also mentioned in the report's safety recommendations) but they never got there, possibly because to some extent they got sidetracked talking to "company" and perhaps convinced by the ground that the engine was ok.

There's a danger to modern comms...

Last edited by wiggy; 22nd Mar 2017 at 08:51.
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Old 22nd Mar 2017, 12:17   #868 (permalink)
 
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Once again. The problem here wasn't that they kept the engine running. I would have done the same (unless told different by the QRH). But I can't understand why they used it for reverse after landing. That is what triggered the fire, not the engine problem in itself.
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Old 22nd Mar 2017, 12:31   #869 (permalink)
 
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I used to be a fan of Singapore Airlines. Flying all over the world. However the past few years that airline has lost my respect. Price of tickets is the highest of any airlines in Asia, service is sometimes times rude and robotic with a hint of arrogance. Accidents such as this one confirm that I made the right choice not to fly with them. And I am not alone thinking like this.
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Old 22nd Mar 2017, 13:46   #870 (permalink)
 
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Quote:
The problem here wasn't that they kept the engine running. I would have done the same (unless told different by the QRH)
You want to stick by the QRH/ECL? Fair enough, absolutely no argument from me, but dare I point out that in that case you wouldn't have done the same as this crew because you would had actioned QRH/ECL fully and correctly, identified an engine fuel leak and shut the offending engine down in flight.

In short on the triple an Engine fuel leak = appropriate engine shutdown on the 777, there's no QRH option/ECL option to keep running at idle and land but not use reverse.
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Old 22nd Mar 2017, 13:50   #871 (permalink)
 
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Of course Wiggy. No arguments about that.
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Old 22nd Mar 2017, 13:59   #872 (permalink)
 
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Sorry, expat we might have crossed in editing.


TBH I do have some sympathy with the SQ crew, it has been shown in the sim that it is entirely possible for anybody to make a complete dogs dinner of the 777 Fuel Disagree/Fuel leak checklist, some of it is down to language used, some of it is being suckered in by logic branches produced by the ECL( Electronic CheckList). You really have to have a hard think about the exact question asked, the fuel system itself and what the checklist is trying to achieve before clicking the "yes" or "no" boxes.

Last edited by wiggy; 23rd Mar 2017 at 08:16.
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Old 22nd Mar 2017, 20:50   #873 (permalink)
 
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I'm with Wiggy on this one. The report doesn't suggest that the SFF ECL was run. If it had been then it would have called for a diversion.
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