Bond ground all UK EC135s
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My understanding is that with main tank transfer pump failure (either or both) or indeed with them switched off, you may end up with a little over 70 kgs stuck in the main tank, depending on AC attitude and which pump(s) are failed/off.
True -
Failure of AFT Transfer pump in hover attitude can result in up to 71 kg unusable.
FWD Transfer pump above 80 knots up to 59 kg unusable.
How it all works here give or take.
Failure of AFT Transfer pump in hover attitude can result in up to 71 kg unusable.
FWD Transfer pump above 80 knots up to 59 kg unusable.
How it all works here give or take.
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Transfer pumps
The NRV valves on the transfer pumps are the weak link in the system. Either stuck open or closed will cause problems with pitch change. At low fuel levels one pump will be above the level of the fuel. My guess is after engine flame out return to level pitch restored fuel to the supply tanks. The popping noise may have been the engines doing there best to relight.
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Main fuel tank
A fractured fuel pipe or loose conection in the tank could have the same effect. Please feel free to shoot me down in flames if you wish. Fuel starvation is the most likely reason for two engines to stop at the same time.
Robin400,
As Donald Rumsfeld said "Known unknowns"
I could give you a million reasons as to why - do any carry much probability?
NO.
This is not a competition to see who ultimately has the answer. There is no prize.
As Donald Rumsfeld said "Known unknowns"
I could give you a million reasons as to why - do any carry much probability?
NO.
This is not a competition to see who ultimately has the answer. There is no prize.
Join Date: Aug 2000
Location: Liverpool based Geordie, so calm down, calm down kidda!!
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Robin, I happen to agree your theory is a good one. You don't know which tank that fuel was in, do you? A simple yes or no will do.
DB:
Isn't fuel lighter than water? 
It would seem that the floats will float to the top of the total volume of fluid, with the uppermost layer being the fuel. (Pour a little water in a jar, pour some gas on that, let is set for a bit, and see which floats to the top. PS: Elfin Safety says "No Smoking" whilst doing this! 
And do it in the garage, as the ball and chain will have a fit if she smells gasoline in the kitchen! )
That said, any water in the tank is displacing a volume of usable fuel that the level of the float would be indicating by its position, so yeah, set up for a wrong indication of how much gas you have usable ...
Back to the case at hand:
From the points being made in the bulletins, it does not appear to be a problem of a signficant volume of water fooling the fuel indicator or low fuel warning system, but a fairly small bit in the wrong place leading to erroneous signals.
jayteeto:
This post intrigues me. Won't ask how you arrived at that conclusion.
EPAC:
The discussion on A330 Thales vs Goodrich pitot tubes strikes a parallel concern. In that case, though, Airbus was in the process of a fleetwide refit ...
Would not the "float" float on the water content thus causing the tanks to overread the amount of "fuel" available anyway regards of where the water is in relation to the fuel.
It would seem that the floats will float to the top of the total volume of fluid, with the uppermost layer being the fuel. (Pour a little water in a jar, pour some gas on that, let is set for a bit, and see which floats to the top. PS: Elfin Safety says "No Smoking" whilst doing this! And do it in the garage, as the ball and chain will have a fit if she smells gasoline in the kitchen! )That said, any water in the tank is displacing a volume of usable fuel that the level of the float would be indicating by its position, so yeah, set up for a wrong indication of how much gas you have usable ...
Back to the case at hand:
From the points being made in the bulletins, it does not appear to be a problem of a signficant volume of water fooling the fuel indicator or low fuel warning system, but a fairly small bit in the wrong place leading to erroneous signals.
jayteeto:
This post intrigues me. Won't ask how you arrived at that conclusion.
EPAC:
Why should a pilot have to be suspicious of a system's integrity and have to 'second guess' it because it doesn't do what it says on the tin. It should meet the criteria of its design approval under common circumstances. If it doesn't, then it should be improved to meet those criteria and at least have a maintenance/ monitoring programme put in place in the meantime.
.....and there are those known things we don't know too!
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re= float- measurement of liquid.
The whole point is, the total volume is measured. It is a given that a certain amount of tank-contents is UNAVAILABLE TO THE PICKUP -This allows for dirt, water and other contaminants to settle clear of the drawoff point.....a well-designed tank would have a low-point sump well away from the pickup and incorporating a transparent sedimenter and drain point. there is absolutely no point in drawing a sample from a higher level,which is why some designs need multiple drain-points.
Having said that, PROVIDED regular sample- drains are carried out, the water coalescing ,is pretty-much irelevant.....IT IS IN THE UNUSABLE "SUMP" AREA
The CONTENTS gauge will show how much usable fuel you have......if a portion of that is water, then you, the Pilot, are guilty of gross incompetence and negligence.....retire immediately!
A Capacitative system, calibrated to a laboratory-standard,pure liquid, is not fit for the purpose of measuring a liquid of "stated" quality. Clearly, there's a tolerance on commercial fuel hudrocarbons...I guess the on-board computers and sensors are not smart -enough to pick up a deviance caused by contaminated fuel....which brings us back to my original proposition....
An electronic system of fuel tank contents measurement is not fit for commercial aircraft operations....it's measurement is arbitrary and dependant on the quality of the fuel.
A sump-drain will not necessarily show water, but that does not mean there is not a high water content dispersed in the fuel itself (see the Heathrow BA crash threads for that one! ) Ultimately, it can precipitate, but you need a very large amount before you have trouble under normal operating and check regimes.
Helicopters have a poorer unpowered flying ability than fixed-wing...therefore it would seem a priority to design any such craft around an "Inherently safe" regime. Eliminate as many traps, "gotchas" and flaws at the design stage...together with good ergonomics, a safer aircraft should ensue.
The whole point is, the total volume is measured. It is a given that a certain amount of tank-contents is UNAVAILABLE TO THE PICKUP -This allows for dirt, water and other contaminants to settle clear of the drawoff point.....a well-designed tank would have a low-point sump well away from the pickup and incorporating a transparent sedimenter and drain point. there is absolutely no point in drawing a sample from a higher level,which is why some designs need multiple drain-points.
Having said that, PROVIDED regular sample- drains are carried out, the water coalescing ,is pretty-much irelevant.....IT IS IN THE UNUSABLE "SUMP" AREA
The CONTENTS gauge will show how much usable fuel you have......if a portion of that is water, then you, the Pilot, are guilty of gross incompetence and negligence.....retire immediately!
A Capacitative system, calibrated to a laboratory-standard,pure liquid, is not fit for the purpose of measuring a liquid of "stated" quality. Clearly, there's a tolerance on commercial fuel hudrocarbons...I guess the on-board computers and sensors are not smart -enough to pick up a deviance caused by contaminated fuel....which brings us back to my original proposition....
An electronic system of fuel tank contents measurement is not fit for commercial aircraft operations....it's measurement is arbitrary and dependant on the quality of the fuel.
A sump-drain will not necessarily show water, but that does not mean there is not a high water content dispersed in the fuel itself (see the Heathrow BA crash threads for that one! ) Ultimately, it can precipitate, but you need a very large amount before you have trouble under normal operating and check regimes.
Helicopters have a poorer unpowered flying ability than fixed-wing...therefore it would seem a priority to design any such craft around an "Inherently safe" regime. Eliminate as many traps, "gotchas" and flaws at the design stage...together with good ergonomics, a safer aircraft should ensue.
unfit electronics
@cockney steve
Seems a bit harsh. Capacitance based sensors seem problematic. There are alternative solid state methods.
e.g. Ultrasonic, optical pulse/time based, optical refractive, thermal using differential heat conductance of air vs fuel.
An electronic system of fuel tank contents measurement is not fit
e.g. Ultrasonic, optical pulse/time based, optical refractive, thermal using differential heat conductance of air vs fuel.
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'Auto like a brick'
re= float- measurement of liquid.
Helicopters have a poorer unpowered flying ability than fixed-wing...therefore it would seem a priority to design any such craft around an "Inherently safe" regime. Eliminate as many traps, "gotchas" and flaws at the design stage...together with good ergonomics, a safer aircraft should ensue.
Helicopters have a poorer unpowered flying ability than fixed-wing...therefore it would seem a priority to design any such craft around an "Inherently safe" regime. Eliminate as many traps, "gotchas" and flaws at the design stage...together with good ergonomics, a safer aircraft should ensue.
Regrettably complexity has unforseeable implications. Simplicity is hard to acheive - but worth it.
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Helicopters have a poorer unpowered flying ability than fixed-wing
A helicopter, nicely established in autorotation, has the ability to manouvre in any direction and we can even keep the autopilot in for stability and speed datum. It can land at 60 Knots or Zero knots (especially in hands of our ex "Nam" brethren).
An airliner is committed to a touchdown at well over 100 knots.
I would suggest the helicopter fares a lot better in unpowered flight, especially at the end.