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Just thinking...The engines sucking in fuel via the inletport of the prime pump.....transfer pumps delivering the fuel from the main tank to the supplytank. Assuming the transfer fuel lines exits situated somewhere on/near the bottom of the supply tank...the fuel flow generated by the transferpumps is way larger than the suction flow to the engine. Is this creating some swirl effect in the supply tank.....when you suddenly stop the supply from the transfer pumps; the swirl will continue for a couple more minutes, creating static pressure drop at the exit of the fuel transfer line, and thus continue pulling fuel from the main tank. The swirl effect slows in time and after some minutes the static pressure drop ceases to exist and the engine starts sucking from the supply tank........ So I think a lot of sucking is involvedhttp://images.ibsrv.net/ibsrv/res/sr...s/embarass.gif so if you did a similar check without switching on the transfer pumps at the beginning of the sequence....no swirl created,.... the supply tanks would start emptying rightaway. (assuming the main tank Qty level is below the overflow channels) skadi |
Sucking fuel for 15 minutes from the main tank to the supply through all that pipeage simply by the pressure difference caused by a swirl that can be reproduced by making a cup of tea …. if only we'd known about this effect before archimedes invented his screw :ok:
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. if only we'd known about this effect before archimedes invented his screw* Yep, because I question things* (also looking forward to your reply on this one) |
Phoinix; We had exactly the same; 159 till 139 after XFER pumps OFF, sucking at it for almost 15' before supply tank indication dropped." |
that's the main reason why I decided to disagree with you on this issue.... p.s. Remember what Viper said about arrogance? Viper |
.. you don't*decide*to disagree. p.s. Remember what Viper said about arrogance? |
I must have missed that Y135, I guess we agree to disagree.
Perhaps there will be some more investigation into this phenomena :ok: |
Yellowbird, I think thats the first plausible explanation since I started this long debate with my simple question... Thanks! With transfer pumps off, Run the supply tanks down until red fuel warning. Shut down the engines. Turn on both transfer pumps, when supply tanks start filling, turn off transfer pumps and monitor the supply tank levels. |
PC,
yep...could be, but I'm not sure whether the suction of a running engine is needed to create this phenomena. I'm not even sure if this actually is the explanation..........I just can't think of anything else. To be honest, I know I have a creative imagination, but I would never have predicted this effect (if it's true) to continue for this long. I think that the boys and girls from Donauwerth might have addressed the "couple of minutes" note in the ASB a little further. I was about to shut down the thing after more than 10 minutes wittnessing the Main tank qty go down, thinking I must have done something wrong.:ugh: Still, I'm almost certain now that this is exactly what happens. |
Donauwörth :}:}
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6 pumps, 4 nrv, 3(4) fuel tanks - still no consensus on how it works - uphill swirl syphoning, I see! certifiable !
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Factory Training
Having read most of the posts regarding this tragic accident there seems to be a great deal of poor understanding of the fuel system.
May respectfully suggest that all crew go on a FACTORY training course ensuring that they fully and correctly understand the systems they are operating. |
..cont from other thread.
I thought you might have been on about transfer pump failures/turned off, with a check valve failure. |
Normal flight ops......use of transfer pumps with low main tank fuel levels.
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brought over from other thread..
AnFI SS - The irony of your post is staggering - the first accident in the AAIB report, you point to, is a double engine stoppage of a twin cause by fuel exhaustion - given that that may also be the case here (and other complete power loss events) it is tempting to conclude that the mathematical assumptions concerning the safety of TWIN ENGINED helicopters is FLAWED - is the rarety of full power loss in twins actually 10^-9 per hour ? Umm, if you care to read the first incident all the way to the end, you'll get to the bit that says, "no action was taken to select an alternative fuel source for the engines after their power loss." Single or twin, if the crew don't switch tanks, the engine will stop :ugh: |
SS
Agree SS
more complexity - more room for human error - more human errors if you have 2 FCL then it is possible to retard the wrong one - if you don't it is not possible.... It is clear that if an 'internet room' full of experts can't work out how a fuel system works that it is probably too complicated - if a system is prone to human failure then it's not totally 'Kosher' to blame pilot's - it's a whole system deal Stats don't support the theory |
I'm really surprised to hear that the fuel system (airframe) is considered complicated, I can imagine people having difficulties (before anyone starts asking......myself included) with the engine fuel system. But a bladder divided in 1 large, 2 small reservoirs, a couple of impeller pumps........how complicated can it be?
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Human factor wise, how is the fuel system being considered complicated?
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yellowbird
I'm really surprised to hear that the fuel system (airframe) is considered complicated, I can imagine people having difficulties (before anyone starts asking......myself included) with the engine fuel system. But a bladder divided in 1 large, 2 small reservoirs, a couple of impeller pumps........how complicated can it be? I thought these are diaphragm not impeller pumps? I'm sure I read that and would seem to me to be the better choice with these low fuel flow rates. |
Fuel system complexity
I total agree that the fuel system is not complicated.
How the system is managed with fuel levels below the weir is where l guess a certain procedure is required. I have asked how you manage the TRANSFER PUMPS to ensure that one is submerged in fuel with the change in pitch attitude with no reply. My understanding is the one pump may be above the fuel and switched off. I thought these are diaphragm not impeller pumps? This is what worries me, if you operated a 135 you should know. Do you not do a tech refresher course. |
May respectfully suggest that all crew go on a FACTORY training course ensuring that they fully and correctly understand the systems they are operating. BC |
I have a cross-section view of the pump from my training notes. It looks to me like an impeller type pump.
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I have asked how you manage the TRANSFER PUMPS to ensure that one is submerged in fuel with the change in pitch attitude with no reply. My understanding is the one pump may be above the fuel and switched off. skadi |
May respectfully suggest that all crew go on a FACTORY training course ensuring that they fully and correctly understand the systems they are operating. Would he have the decency to explain the whys an wherefores of this extraordinary accusation, and what evidence he has to support it? Or else perhaps to apologise fulsomely for such an unwarranted slur against the Professionalism of those crew alluded to? For shame.:ugh: |
I thought these are diaphragm not impeller pumps? I'm sure I read that and would seem to me to be the better choice with these low fuel flow rates. |
Robin400 - I'm sure if I ask nicely my CP wont mind if I and the other 70 odd pilots nip over to Germany for a few days at the company's expense for a bit of fuel system training and sightseeing. God knows I could do with it this time of year... All part of the expense running a safe professional outfit. Maybe the concern in Germany will pay the bill |
FFS, guys, why so confrontational?
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My posts are not intended to be a slur on all pilots involved in the operation of the 135, if you feel that that is the case I apologise unreservedly. I accept that all the posts on here are not from 135 pilots.
From the posts on here I am left with a sense of unease regarding the level of understanding. |
Thats the procedure according FLM. A dry running fuelpump gives a CAUTION and has to be switched off. So when in hover atttitude, the FWD pump will be the first when the main tank is coming to around 60 kg. In cruise flight ( nose low ) it will be the AFT pump. You have to consider it, when transitioning to cruise after long hover flight and low fuel in main tank -> AFT pump off and FWD pump ON again!!! Skadi. :D Thank you very much. That is exactly as I imagined it would be. |
All part of the expense running a safe professional outfit There seems to be a lot of concern about pilot familiarity and understanding of the 135 fuel system on this thread from non 135 people. The system hasn't changed markedly from when I was taught about it 7 years ago and I am still happy with how it operates practically day to day as a pilot. I don't feel I need further training and as to all the minute design intricacies etc. I am happy to leave that to the engineers and boffins in white coats. BC |
10 pages of disagreements about how the fuel system works - uphill syphoning , swirl, pump types, CoG attitude changes, ltrs / kgs water in capacitive fuel senders, confusion about wether one engine should stop first or both might stop at about the same time - leads me to beleive that the understanding amongst the population of 135 pilots is clearly appropriate (not) - carry on.
Anyone with a clear understanding of the system care to explain what scenario leads to a double engine stoppage ? Just incase there is any 135 pilot out there who doesn't know.. What are the combinations of possible failure with 12 hoses 6 fuel pumps and 4(?) non-return valves - does the pilot need to understand that? No - not if it's all working properly i guess. Remember the A109 in Wales because of the misunderstanding of a transfer pump failure? |
Quote: Thats the procedure according FLM. A dry running fuelpump gives a CAUTION and has to be switched off. So when in hover atttitude, the FWD pump will be the first when the main tank is coming to around 60 kg. In cruise flight ( nose low ) it will be the AFT pump. You have to consider it, when transitioning to cruise after long hover flight and low fuel in main tank -> AFT pump off and FWD pump ON again!!! Skadi. :D Thank you very much. That is exactly as I imagined it would be. skadi |
AnFi,
Anyone with a clear understanding of the system care to explain what scenario leads to a double engine stoppage ? Just incase there is any 135 pilot out there who doesn't know.. There is also a very good post by Giovanni cento nove back in 2004 I think, about the 135 fuel system, but can't remember what thread. Ah just found it! Post 83 this thread. |
Post 83 on this thread
Gosh!! what a knowledgeable piece of writing. :D
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the post from 83 to 114 are essential reading for 135 pilots. Complexity and permutations as described there make 'pilot error' inevitable - it's a shame they call it pilot error...
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Complexity and permutations as described there make 'pilot error' inevitable - it's a shame they call it pilot error... |
Up to date 44% of the whole fleet have been checked and 2% had faulty indications:
EC135 fuel probe malfunctions in 2% of cases - 1/14/2014 - Flight Global skadi |
Do you not realise, the people from the Crash thread also post on here, so your answers aren't going to be any different. :ugh:
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Originally Posted by Robin400
(Post 8279953)
I am sorry for being a pain,I have been banned from the Glasgow forum for asking to many dumb questions.
Rotorheads A haven for helicopter professionals to discuss the things that affect them |
Trying to bring the fuel talk here, rather than the Glasgow thread.
AnFI (really!)
It is patently obvious that, with such a high unuseable fuel quantity, the cockpit situation faced by this pilot may well have left him with an excessively confusing and unexpectedly complex set of actions. Maybe unpredictable issues of timing wrt Governor response rates and pilot action. Everything points to that. LOW FUEL 1 and/or2 Check fuel contents If pos contents, check XFER pumps on Check cb's in If remains on, switch off bleed air Land within 10 mins (That Land being an immediate action!) |
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