Police helicopter crashes onto Glasgow pub
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40odd2 --
The history is as I said. Fuel is sold by mass (kg) and the energy value of the fuel is adjusted in the refinery to meet a specified range of specific energy values (MJ/kg, or kWh/kg, for example). What the pilot needs to know is how much energy he has in his tanks (just as applicable to gasoline as to gas turbines) and the mass he is carrying, for MTOW and COG calculations, for example. Litres is a unit that serves the pilot no use. Just work in kg and convert all non-kg values to kg. It's not something the pilot can just elect to do, or any manufacturer, and it's unlikely to be anything to do with this accident....but it would help safety by reducing the number of calculations the pilot has to do.
The history is as I said. Fuel is sold by mass (kg) and the energy value of the fuel is adjusted in the refinery to meet a specified range of specific energy values (MJ/kg, or kWh/kg, for example). What the pilot needs to know is how much energy he has in his tanks (just as applicable to gasoline as to gas turbines) and the mass he is carrying, for MTOW and COG calculations, for example. Litres is a unit that serves the pilot no use. Just work in kg and convert all non-kg values to kg. It's not something the pilot can just elect to do, or any manufacturer, and it's unlikely to be anything to do with this accident....but it would help safety by reducing the number of calculations the pilot has to do.
Lemain,
Sorry to disappoint you but, and I have just checked, all of our fuel orders and deliveries are in litres. Our pump dispenses in litres and the sign on the side of the bulk fuel tank gives it's maximium capacity in litres. At some point, somebody has to do the conversion and, certainly in police aviation, that person is the pilot. Now, as I previously said, if you can come up with a pump that dispenses in kgs................
"What the pilot needs to know is how much energy he has in his tanks"
So, you're telling me I've been doing it all wrong for the last 30 years??
All I'm interested in is that it's Avtur, how much it weighs and that I have enough of the stuff to enable me to get to where I need to go and do what I need to do.
Sorry to disappoint you but, and I have just checked, all of our fuel orders and deliveries are in litres. Our pump dispenses in litres and the sign on the side of the bulk fuel tank gives it's maximium capacity in litres. At some point, somebody has to do the conversion and, certainly in police aviation, that person is the pilot. Now, as I previously said, if you can come up with a pump that dispenses in kgs................
"What the pilot needs to know is how much energy he has in his tanks"
So, you're telling me I've been doing it all wrong for the last 30 years??
All I'm interested in is that it's Avtur, how much it weighs and that I have enough of the stuff to enable me to get to where I need to go and do what I need to do.
Avoid imitations
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With regard to fuel contents, at least things have moved on a little.
With the police helicopter I flew, with a crew of three, we could only ever take off with half tanks, for reasons of all up weight. The fuel used to be dispensed in litres, but the RFM figures were in Kgs. However! The fuel contents gauges were marked in per cent (yes, %).
To make it easier at base, for rapid refuels where I knew the fuel flow of the dispensing pump, I used to refuel using the second hand on my watch.
Worked every time.
With the police helicopter I flew, with a crew of three, we could only ever take off with half tanks, for reasons of all up weight. The fuel used to be dispensed in litres, but the RFM figures were in Kgs. However! The fuel contents gauges were marked in per cent (yes, %).
To make it easier at base, for rapid refuels where I knew the fuel flow of the dispensing pump, I used to refuel using the second hand on my watch.
Worked every time.
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Conversions
Performing conversion calculations is nothing new to any commercial helicopter pilot. How many hours did we spend doing conversions like litres to kg, gallons to lbs, lbs to kg, sm to nm, mph to kts etc. for commercial exams? Back in those days the whizz wheel was your best friend... 
Purveyor of Egg Liqueur to Lucifer
DB;
Sid, 95 litres is a value very similar, give or take the SG for the OAT, to the 71-72 KGS of fuel that becomes unusable should both main tank transfer pumps fail or be selected off.
I think that makes the value of 95 litres interesting and could be significant. However it is the AAIBs job to determine the associated facts that would gives us a better insight into how this accident occurred.
Sid, 95 litres is a value very similar, give or take the SG for the OAT, to the 71-72 KGS of fuel that becomes unusable should both main tank transfer pumps fail or be selected off.
I think that makes the value of 95 litres interesting and could be significant. However it is the AAIBs job to determine the associated facts that would gives us a better insight into how this accident occurred.
So in reality, we come back to the 95 litres still just simply being, 'the amount drained'.
Presumably the extra weight and complexity of a densitometer, as used on large aircraft, to permit automated fuel volume to mass calculations is deemed unnecessary in helicopters?
Provided one's fuel is of pretty consistent quality, then even a simple fuel temperature measurement should be sufficient to enable an automated volume to mass conversion?
Provided one's fuel is of pretty consistent quality, then even a simple fuel temperature measurement should be sufficient to enable an automated volume to mass conversion?
With regard to fuel contents, at least things have moved on a little.
With the police helicopter I flew, with a crew of three, we could only ever take off with half tanks, for reasons of all up weight. The fuel used to be dispensed in litres, but the RFM figures were in Kgs. However! The fuel contents gauges were marked in per cent (yes, %).
To make it easier at base, for rapid refuels where I knew the fuel flow of the dispensing pump, I used to refuel using the second hand on my watch.
Worked every time.
With the police helicopter I flew, with a crew of three, we could only ever take off with half tanks, for reasons of all up weight. The fuel used to be dispensed in litres, but the RFM figures were in Kgs. However! The fuel contents gauges were marked in per cent (yes, %).
To make it easier at base, for rapid refuels where I knew the fuel flow of the dispensing pump, I used to refuel using the second hand on my watch.
Worked every time.
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ShyT, one question. How often was the pump flow rate checked? Pump capacity can decrease over time. ?????
FYI,
The 135 FUEL QTY units can be configured to just about whatever unit you want by CONFIGURATION page.
Apparently there is not much demand for it.
The 135 FUEL QTY units can be configured to just about whatever unit you want by CONFIGURATION page.
Apparently there is not much demand for it.
Avoid imitations
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ShyT, one question. How often was the pump flow rate checked? Pump capacity can decrease over time. ?????
-------------------------
I see folks here are now getting concerned about relatively insignificant density differences in the fuel. Put it in perspective, chaps!
For example, an aircraft with a "500 Kg" fuel tank (for round figures) fills up with 0.8 SG fuel. It will have taken 625 litres.
Next time it is filled, the fuel is 0.81 SG. It will "only" have 617.3 litres on board. A difference of 7.7 litres / 1.7 gallons, or approx 6 Kgs difference @ 0.81 SG.
Obviously, the fuel gauges and fuel flow meters still work, irrespective of a small error in SG and such a small mass will have a very small effect on aircraft performance. When performance is most critical, at takeoff and landing, a small wind variation will probably have more of an effect.
I certainly don't lose any sleep over it because I would land before the gauges showed 6 kgs total, whatever the circumstances. My present aircraft's stated unusable fuel is 5 Kgs /5 Kgs (approx 12 litres total).
Thankfully, from what I've read here, the fuel system is far more straightforward than that of the EC135. It has one transverse main tank, connected by gravity to a pair of smaller tanks, one feeding each engine.
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I know nothing about the practicalities of a/c fuel loading, so forgive me if I've missed a critical assumption or two, but ST's example above seems a little odd.
A fuel tank described as having "500kg" capacity is the problem.
Tanks have volumes, not weights. The "500kg" description would be a nominal one based on the tank volume and a nominal fuel density. If the tank was "brimmed", then the weight carried would be the tank maximum volume [multipled] by the fuel density.
If it was brimmed with a different density fuel, then the mass would change but the volume would not.
However, if the tank was loaded using some kind of mass flow meter to ensure that 500kg was loaded, then the example 625/617 litre thing would happen, provided the maximum tank volume was greaterr tha nthe fuel loaded, obviously.
But, my understanding from prior posts is that fuel bowsers dispense by volume, not by mass?
Confused, I am.
Edit: So confused that I can't tell my multiplies from my divides. oops.
A fuel tank described as having "500kg" capacity is the problem.
Tanks have volumes, not weights. The "500kg" description would be a nominal one based on the tank volume and a nominal fuel density. If the tank was "brimmed", then the weight carried would be the tank maximum volume [multipled] by the fuel density.
If it was brimmed with a different density fuel, then the mass would change but the volume would not.
However, if the tank was loaded using some kind of mass flow meter to ensure that 500kg was loaded, then the example 625/617 litre thing would happen, provided the maximum tank volume was greaterr tha nthe fuel loaded, obviously.
But, my understanding from prior posts is that fuel bowsers dispense by volume, not by mass?
Confused, I am.
Edit: So confused that I can't tell my multiplies from my divides. oops.
Last edited by David Bass; 4th Jan 2014 at 17:37.
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I see folks here are now getting concerned about relatively insignificant density differences in the fuel. Put it in perspective, chaps!
Avoid imitations
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David, it's not strange, there is no problem and there is no confusion amongst pilots.
Helicopter fuel gauges are often calibrated in Kgs because as pilots we have to calculate the aircraft AUM as the greater priority. The SG of fuel changes very little, in the big picture. I quoted an example to show how little a different SG affects the contents of the tanks.
If we wanted it to be really difficult we could calculate passengers weights by the litre and their exact SG, too.
As long as the gauges show when there is fuel in the tanks and I have a conversion factor for their calibration I couldn't really care if it says 500 litres, 500 Kgs, or 500 bananas on the scale.
Helicopter fuel gauges are often calibrated in Kgs because as pilots we have to calculate the aircraft AUM as the greater priority. The SG of fuel changes very little, in the big picture. I quoted an example to show how little a different SG affects the contents of the tanks.
If we wanted it to be really difficult we could calculate passengers weights by the litre and their exact SG, too.
As long as the gauges show when there is fuel in the tanks and I have a conversion factor for their calibration I couldn't really care if it says 500 litres, 500 Kgs, or 500 bananas on the scale.
David, it's not strange, there is no problem and there is no confusion amongst pilots.
Helicopter fuel gauges are often calibrated in Kgs because as pilots we have to calculate the aircraft AUM as the greater priority. The SG of fuel changes very little, in the big picture. I quoted an example to show how little a different SG affects the contents of the tanks.
If we wanted it to be really difficult we could calculate passengers weights by the litre and their exact SG, too.
As long as the gauges show when there is fuel in the tanks and I have a conversion factor for their calibration I couldn't really care if it says 500 litres, 500 Kgs, or 500 bananas on the scale.
Helicopter fuel gauges are often calibrated in Kgs because as pilots we have to calculate the aircraft AUM as the greater priority. The SG of fuel changes very little, in the big picture. I quoted an example to show how little a different SG affects the contents of the tanks.
If we wanted it to be really difficult we could calculate passengers weights by the litre and their exact SG, too.
As long as the gauges show when there is fuel in the tanks and I have a conversion factor for their calibration I couldn't really care if it says 500 litres, 500 Kgs, or 500 bananas on the scale.
And (does'nt matter in this case) hte fuel consumtion for a given task is in kilograms. If the SG is lower, there fuel consumption in liters will be higher. So, if calculated in kilograms theres no need to recalculate the fuel consumtion (in liters) depending on temperature.
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And (does'nt matter in this case) hte fuel consumtion for a given task is in kilograms. If the SG is lower, there fuel consumption in liters will be higher. So, if calculated in kilograms theres no need to recalculate the fuel consumtion (in liters) depending on temperature.
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But a mistake would show up on the fuel gauge in the cockpit.
Btw, all this semantic discussion about fuel related helicopter accidents.... The cause of this tragic one may not be fuel starvation.
Btw, all this semantic discussion about fuel related helicopter accidents.... The cause of this tragic one may not be fuel starvation.
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But a mistake would show up on the fuel gauge in the cockpit.
Btw, all this semantic discussion about fuel related helicopter accidents.... The cause of this tragic one may not be fuel starvation.
Btw, all this semantic discussion about fuel related helicopter accidents.... The cause of this tragic one may not be fuel starvation.
Was the pilot incapacitated? Has not been stated either way.
Did the pilot make a flying mistake that he failed to rectify?
Was the aircraft wholly or partly un-flyable? (e.g. fuel, mechanical failure)
It is possible that the cause is included in all of the above.
For example, the pilot was under the influence of some substance and took off with less fuel than he thought. Concentrating on the mission, believing he had 'plenty' of fuel, he didn't focus on the fuel. When the fuel warning came on, some distance from base, he was taken by surprise and became disoriented, perhaps due to the drugs. The pilot commenced a manoeuvre in an uncoordinated manner losing altitude to the point that he considered that to land on the apparently safe black block below him was a safer strategy than recovery and return to base.
There is no evidence whatsoever to support that or rule it out....at least not evidence available to PPruNe posters. Furthermore, it seems unlikely given the service record of the pilot. Until some other hard information comes to light, we haven't got anything more to go on.
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The semantics are getting more unlikely still. If the pilot had turned up for work in a situation where he was unfit, the two police observers who were in close proximity to him throughout might just have observed that something wasn't quite right.
Especially as they would no doubt have previously dealt with members of the public who were in that situation.
Especially as they would no doubt have previously dealt with members of the public who were in that situation.
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ShyTalk -- You're probably right. I doubt it's the answer. But nothing so far makes too much sense because there has been no safety check on other a/c other than fuel instruments which look unconnected with this. Whatever happened IS extremely unlikely. If it was likely, then 'they' wouldn't have let the a/c fly!