Police helicopter crashes onto Glasgow pub

[Old and Horrified]

So we now have yet another contributor who refuses to say their background spouting yet more drivel. This last post is mind-boggling in its inanity. Maybe they are actually all the same guy with different user names?

[AnFI]

well OH - not taking that seriously? you think the first engine would just wind down placidly? (Very high unusable has differnt implications to a small unuseable) Or are you just a zero contribution too?

[ShyTorque]

While you're up there doing your test pilot stuff, AnFI (it'll have to be you, because you won't find a sane test pilot who will carry out your proposal), why not ask them if you can practice tail rotor driveshaft and other potentially catastrophic failures, too?

In the words of John MacEnroe......

[Fortyodd2]

AnFI,
Take one gas blow torch, turn the gas on and light it - this is engine running.
Put your lighter away out of reach.
Now turn the gas off for half a second and back on again.
Question - is the flame still there?

[AnFI]

i am really surprised that nobody takes seriously that the intermitency of fuel supply (which you would get with a very high 'unusable' fuel) could lead to a very awkward cockpit scenario..

Fortyodd - no - I think, with AutoRe-light, that the engine would not just cleanly stop.
Quite alot of popping as described by witnesses. I don't think it is the same as shutting gas off for a whole 1/2 second - perhaps much shorter partial fuel interruptions. Gas interuptions of 1/100th second would probably not lead to the flame going out.

Shytorque - do you think running out of fuel in the first engine should be catastrophic as you seem to recognise that this might be? It shouldn't be so dangerous that a test pilot would be insane to test it - should it?

Do we know here the Fadec logic for this A/C? Does it auto-shut down with slightly interupted fuel supply?

[Fortyodd2]

AnFI,
You may be interested in this quote from the EC135 training course notes:
"After attaining self sustaining speed of 50% N1 the start relay disconnects the ignition circuit. From this point on, combustion of the fuel/air mixture continues without the aid of outside ignition".
The compressor is spinning at 54,000rpm and the power turbine at 44,000rpm - when the fire goes out, it goes out quickly and the fire stays out. There is no auto re-light.
For a restart in flight, the N1 must be below 17% and the engine main switch must start from the "Off" position. If the switch is moved from "Off" to "Idle" before the N1 is below 17% then nothing will occur until that level is reached.
When a gas turbine is shut down correctly, there are several processes that occur to ensure that the engine is not damaged, injectors do not become coked or bearings do not get carbon'd. If an engine suffers a "Flame out" then it is withdrawn from service until it has had an engineering inspection.

[AnFI]

Thanks FO2 - effectively same as any turbine engine.

If it is the case that the engine goes out cleanly then there is negligable risk to test that then - if however it is not so simple then this should be known.

It may not be so simple in the case where the unuseable fuel quantity is SO high - the 'running out of fuel' part not being at an intstantaneous event but rather a very gradual partial fuel supply - am I getting that point across or not?

I would guess that the fuel to the combustion chamber does not hit zero but instead has a period of wild variation for some period prior to eventual flame out.

I'd hate the point to be dismissed without anyone actually understanding the point. Understand it and then dismiss it with some facts by all means.

I am amazed that anyone thinks it would be dangerous to allow one engine to flame out under controlled conditions - and if it is that dangerous then perhaps it shouldn't be?

Maybe the AAIB will consider the point more carefully than the experts on this forum?

[ShyTorque]

AnFI, have you ever heard of the term "hard engagement"?

[Fortyodd2]

AnFI,
The place to let an engine "Flame out" under controlled conditions is at the factory.
Like most gas turbines, the Arrius in the 135 has a preferential injector - one that is not supplied via the metering valve. It's job is to keep the flame alight in the event of rapid deceleration of the engine. It is checked during maintenance to ensure that it does just that. But, like all the others, if it starts blowing air then the fire is out. There is only one fuel supply line to the engine.

[Tandemrotor]

Is anyone able to tell me what the practical difference would be between a HIGH unusable fuel figure, and a LOW unusable figure?

Isn't the significant term in both cases the word 'unusable'?

[zorab64]

TR - I'd agree, the discussion of "High" & "Low" unuseable fuel is a red herring IHMO. Reports of "spluttering" & "sparks" add confusion to the mix for those large numbers of us who have managed to fly twin turbines for enough years not to have experienced either. I've flown to 60kgs in a 135 with no problems, save for close monitoring/re-calculating of the total quantity in the final few miles, out of nervousness that I had the longer range calculations wrong. Three amber captions already, with two red ones & their accompanying bongs completing the set just before, & just after, the skids touched the ground, perfect.

I digress - if the discussion centres on unusable fuel, the real question is why the recovered fuel may not have been getting to the engines, given that most of it should have been useable, certainly enough to get back to base & land safely anyway, even if significantly below MLA.
So long as the correct (depending on attitude), or both, transfer pump/s was/were switched on & working, there should have been adequate supply to both engines, whether the quantity readings were correct or not.

40odd - I'd agree completely, and wherever you choose to test fuel starvation, do it with both skids planted firmly on the ground!

As I've already said, whilst there may have been an unfortunate system failure or two, I can't believe all warnings were conincidentally inoperative as well, sadly.

[PieChaser]

Talkpedlar,

Sorry I have just noticed your question.

Piechaser?
Your comments in 1904 and 1907 for starters. I never wish to offend but where did you trawl that garbage from?

Sorry but your lack of appropriate knowledge, experience and intelligence just shine through.

Post 1904

As I see it, failure of a NRV or the fuel transfer pipe would trap fuel in the main tank, starving the supply tanks and ultimately the engines.

The FAA fuel system requirements are:
Fuel System Independence
Each fuel system for a multiengine airplane must be arranged so that, in at least one system configuration, the failure of any one component (other than a fuel tank) does not result in the loss of power of more than one engine or require immediate action by the pilot to prevent the loss of power of more than one engine.

Eurocopter being such a huge company would have this covered, ....wouldn't they?

That "Garbage" as you call it, came from our FAA aircraft maintenance manuals, here's a link for you :http://www.faa.gov/regulations_polic...a/ama_ch14.pdf

I realise this could be my last allowable post, so I would just like to say.
The reason I first posted on Pprune was because of the tragic accident involving a fellow aviator. As an engineer and having built my own aircraft (including the fuel system) I was drawn to the design of the 135 fuel system, and All my posts relate to this. I have no motives or hidden agenda, I never want to offend and have always tried to be polite. Surely the whole idea of a forum like this is to bring fellow aviators together and hopefully make the skies a safer place!

Thanks
PieChaser

[awblain]

Pie Chaser,

Your quote about fuel system requirements seems to fit perfectly with the accident aircraft.

There's no obvious way that a single break in the supply tank filling pipe, or a single failure of a fuel pump or valve would starve both engines.

There is also a rider in the statement: "in at least one system configuration". That seems to agree with Eurocopter meeting the certification condition without any doubt. It's very loosely written, but I'm sure their submissions for certification satisfied it.

If there was something weird going on with fuel, and there was no obvious "fuel tank failure", with plenty of fuel left in the wreckage, then I'm sure the investigators will get to the bottom of it eventually.

[AnFI]

Originally Posted by Tandemrotor

Is anyone able to tell me what the practical difference would be between a HIGH unusable fuel figure, and a LOW unusable figure?

Isn't the significant term in both cases the word 'unusable'?

Thank you for paying attention - yes there is a huge difference between a high and a low unuseable quantity - surprisingly.

Try this parallel:
Imagine 'sucking' water out of a swimming pool with a (fixed) straw compared to the same process with a a thimble. When can it be said that you can't get anymore water up the straw? In the case of the thimble it would be well defined, but for the swimming pool there would be a very long duration with some degree of air introduced.


So if the 'sump' were shot-glass sized the 'out of fuel moment' would be very well defined. (as in small unuseable)


If it were fuel being blown up a partially submerged tube orifice there would be air and fuel pushed up the pipe (by the atmosphere) - the pump would foam it (?) and push a fuel foamed mixture onward - I would be surprised if the engine would just stop cleanly at the first hint of slightly aerated fuel - like fortyodd and zorab are so sure it would - I don't think so - it could be a drawn out period of very odd power delivery and perculiar characteristics, perhaps difficult to control or interpret, if the unuseable quantiy is high compared to the flow rate.


I had an obscure fuel system issue previously and it turned out to be caused by foaming JetA1 - nearly caused me a major problem.
Maybe this problem does not apply here for some reason - I don't know (do you?)

[Pozidrive]

AnFI,

Diesel road fuel has anti-foam additive. This makes it easier to get a full tank without a load of froth on top, and probably helps to avoid the problem you describe if the tank is run very low.

Suggest either foam or entrained air from a partially submerged intake would have same result on an engine, IC or turbine.

[Ornis]

There's no obvious way that a single break in the supply tank filling pipe, or a single failure of a fuel pump or valve would starve both engines.

In cruise attitude will the rear transfer pump reach the last ~95 litres? Wouldn't failure to supply one engine mean failure to supply both?

There is also a rider in the statement: "in at least one system configuration". That seems to agree with Eurocopter meeting the certification condition without any doubt. It's very loosely written, but I'm sure their submissions for certification satisfied it.

No doubt. DH Comet was certified? Concorde?

[CRAZYBROADSWORD]

This thread is just like Eastenders you can ignore it for a week or a month and when you come back nothing has changed

[Rigga]

2002 posts now and still nothing productive or positive to say.

Dead-Enders would be better and more taxing entertainment.

[SilsoeSid]

..... and at least a thousand must be on the fuel system alone, posts that should be on the 135 thread.

[Rigga]

Why? Were they some use to anyone?