Police helicopter crashes onto Glasgow pub
PieChaser
"In normal flight when aft transfer pump warning illuminates, you would turn it off, yes?"
Not necessarily.
In the cruise, yes. On scene, hover or low speed orbit, fwd or aft, no -simply because there are constant attitude changes.
In the cruise, in the situation you describe, I would be expecting the main tank quantity to continue to reduce - if instead, the supply tanks start going down then that is the first indication that all is not well - not the Amber caption.
"The two supply tanks contain 115ltrs when full. What's really eating at me is only 95ltrs drained by AIB"
What has not been confirmed yet is which tank?, all tanks?, did they drain some fuel or all fuel?
Moody quantity sensors in the 135 is not a new phenomenon.
"In normal flight when aft transfer pump warning illuminates, you would turn it off, yes?"
Not necessarily.
In the cruise, yes. On scene, hover or low speed orbit, fwd or aft, no -simply because there are constant attitude changes.
In the cruise, in the situation you describe, I would be expecting the main tank quantity to continue to reduce - if instead, the supply tanks start going down then that is the first indication that all is not well - not the Amber caption.
"The two supply tanks contain 115ltrs when full. What's really eating at me is only 95ltrs drained by AIB"
What has not been confirmed yet is which tank?, all tanks?, did they drain some fuel or all fuel?
Moody quantity sensors in the 135 is not a new phenomenon.
Last edited by Fortyodd2; 2nd Jan 2014 at 07:38. Reason: Spooling mistuck
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non return valve stuck open with related pump off
Can someone explain to me how one pump can transfer fuel to the supply tanks if the other transfer pump is off and its nrv is stuck open. Thanks.
Ornis, would depend on the internal design of the pump,and fuel under pressure would take the path of least resistance,which looking at the tank schematic would be to flow into the aft supply tank,rather than through a pump; unless someone has a cutaway of the pump..?
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Fortyodd2
[QUOTE][, I would be expecting the main tank quantity to continue to reduce - if instead, the supply tanks start going down then that is the first indication that all is not well - not the Amber caption./QU
That's exactly what I was trying to say. No audible or visual warnings other than the outer bars lower than the centre on the fuel screen.
I agree with you, as I said in a previous post it's crucial where the AIB drained the fuel from.
[QUOTE][, I would be expecting the main tank quantity to continue to reduce - if instead, the supply tanks start going down then that is the first indication that all is not well - not the Amber caption./QU
That's exactly what I was trying to say. No audible or visual warnings other than the outer bars lower than the centre on the fuel screen.
I agree with you, as I said in a previous post it's crucial where the AIB drained the fuel from.
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The way I see it, is the AIB want us to know that both engines and drivetrain were serviceable and stopped and that the 95 litres of fuel drained was all that remained in the aircraft. Otherwise why bother telling us anything?
The fuel on board at start of ops is known.
The total time of flight is known.
The fuel burn can be calculated.
So with that in mind I am willing to bet that 95 litres is what remained. The supply tanks hold 115 litres, so if both transfer pumps were on and working correctly, then the main tank would be empty and the supply tanks less than full.
Add unusable fuel into the mix and maybe you can see why I think the fuel system design is questionable.
The fuel on board at start of ops is known.
The total time of flight is known.
The fuel burn can be calculated.
So with that in mind I am willing to bet that 95 litres is what remained. The supply tanks hold 115 litres, so if both transfer pumps were on and working correctly, then the main tank would be empty and the supply tanks less than full.
Add unusable fuel into the mix and maybe you can see why I think the fuel system design is questionable.
I'm struggling to understand your point.
You are willing to speculate (and bet) on design issues based on one crash case whilst the problem is not so obvious to the investigators. Even more, there are more than 1000 serials are out there operating with no fuel system design problems, but you see one.
I bet your mind must be an interesting place.
You are willing to speculate (and bet) on design issues based on one crash case whilst the problem is not so obvious to the investigators. Even more, there are more than 1000 serials are out there operating with no fuel system design problems, but you see one.
I bet your mind must be an interesting place.
Purveyor of Egg Liqueur to Lucifer
AAIB
Sorry Pie, I don't see the part that says, 'the 95 litres of fuel drained was all that remained in the aircraft'.
Because if they didn't have an initial Special Bulletin, there are some out there that would believe there was a conspiracy going on 
Once removed from the building, approximately 95 litres of fuel were drained from the fuel tank system
Otherwise why bother telling us anything?
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Oh but I think it is obvious to the investigators.
But maybe you think it's pure coincidence that a SIN and ASB has been issued by EC Concerning the fuel system?
I do agree though, my head is hurting with all this!
But maybe you think it's pure coincidence that a SIN and ASB has been issued by EC Concerning the fuel system?
I do agree though, my head is hurting with all this!
An apology in advance if this has been covered elsewhere.
However the fuel system in question seems to be similar to the original BO 105 system.
This was found wanting by the UK CAA and a modification called the fuel back up system was introduced.
This consisted of a series of check valves and additional piping that allowed all the fuel in the main tanks to be available even if both transfer pumps in the main tank had failed.
All UK BO 105D models had this fitted.
However the fuel system in question seems to be similar to the original BO 105 system.
This was found wanting by the UK CAA and a modification called the fuel back up system was introduced.
This consisted of a series of check valves and additional piping that allowed all the fuel in the main tanks to be available even if both transfer pumps in the main tank had failed.
All UK BO 105D models had this fitted.
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NRV s
I'm not from the aircraft industry, but an engineer, in my game a check valve jamming shut against a positive head is virtually unheard of, usual failure mode is to pass in the other direction, though I am used to higher pressures and water / oil, not kerosene type fuels at low pressure.
Can a helicopter engineer comment, as I don't feel this is a likely failure mode.
Can a helicopter engineer comment, as I don't feel this is a likely failure mode.
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CJ,
At last a fellow engineer to bounce off!
The check valve is fitted just above the the pump, when the pump is on the valve lifts of its seat.
The valve returns to its seat when the pump is off and the other pump is turned on.
Now my experience with check valves is they usually stick off their seat ( the culprit usually being dirt or sediment ) allowing fuel to flow back through the valve.
Are you saying that in your experience, a valve would normally stick on its seat and prevent flow at all?
At last a fellow engineer to bounce off!
The check valve is fitted just above the the pump, when the pump is on the valve lifts of its seat.
The valve returns to its seat when the pump is off and the other pump is turned on.
Now my experience with check valves is they usually stick off their seat ( the culprit usually being dirt or sediment ) allowing fuel to flow back through the valve.
Are you saying that in your experience, a valve would normally stick on its seat and prevent flow at all?
On the Whirlwind Mk 10 there is a small fuel line from the forward pump outlet leading back to the tank with a NRV. On one occasion the NRV stuck open when the pump failed and with the engine sucking fuel allowed air in the system as the line ended above the fuel level and the engine flamed out. After that there was a procedure to switch off the pump with the engine running to ensure that the NRV was working.
Last edited by Oldlae; 1st Jan 2014 at 13:54. Reason: More detail
Pie,
"Do you think there was more than 95 litres remaining?"
I know you directed this question at Sid and I'm not answering on his behalf but, all those of us not on the investigation team can be sure of, is that however much fuel was in the tanks at the time of impact, 95 litres was removed.
If you want some more in depth info on the fuel system, PM me your e-mail and I'll dig out my training notes.
"Do you think there was more than 95 litres remaining?"
I know you directed this question at Sid and I'm not answering on his behalf but, all those of us not on the investigation team can be sure of, is that however much fuel was in the tanks at the time of impact, 95 litres was removed.
If you want some more in depth info on the fuel system, PM me your e-mail and I'll dig out my training notes.