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Granny fuel

Old 24th Apr 2013, 21:01
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essentially brain-washed into believing that their fuel quantity gauge is precisely 200 lbs over-reading (requiring 200 lbs of granny fuel - some use more) yet believe that the fuel totalizer is accurate.
Hmmm, on a KingAir 200 I flew for 10 years, we had several discrepancies in the gauges, yet the totalizer was actually very accurate, always.
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Old 24th Apr 2013, 21:15
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A quick Google suggests its a North American thing.... the term seems to be "granny gas".

There seem to be multiple mentions of it on one Canadian website in particular (stick site:avcanada.ca Granny Gas into Googoo)

One post on that forum even goes as far as stating the following......

Unfortunately the concept of “granny gas” has become an industry standard, particularly for operations north of the 60th parallel. After conduction many long range trips with “granny gas” on board, the pilot eventually will consider this normal operation and not consider this to be a foolish act.
Or another example from the many on that website.....

There seems to be some confusion over the term, "granny gas". Contingency fuel is that above the normal legal amount the crew decides to carry over and above the legal minimum. Granny gas, is that extra 45 minutes the crew "hides" from the prying eyes of the dispatcher. It remains incognito, so to speak until that rare day when it's needed. It used to be very, very, very common practice. I know it saved my bacon once. I'd almost forgotten the extra 60 gallons I "hid" in the Racer, till one day, the tanks we were using blew

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Old 24th Apr 2013, 21:20
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Hmmm, on a KingAir 200 I flew for 10 years, we had several discrepancies in the gauges, yet the totalizer was actually very accurate, always.
What evidence did you have that the totalizer was very accurate?

The gauges on the plane in question seem to be quite accurate. They are calibrated by maintenance on a specific schedule. They are calibrated at the 0 lbs usable fuel quantity, and the 1000 lbs usable fuel quantity. During calibration they will always ensure that what you have on the gauges represents at least what you have in the tanks, erring on the conservative side.

The more I look into this issue, the more I seem to find reason for not taking 'granny fuel'. I've found in my informal survey that pilots tend to state their beliefs as fact. For example, pilots stating that the gauges are inaccurate or that the government regulating agency takes 'granny fuel', yet when asked for any evidence of either one they can't provide any. Not saying that you don't have any evidence for the gauges being inaccurate!

And if there is a discrepancy in the fuel indicating system it should be snagged and the MEL consulted.
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Old 24th Apr 2013, 22:50
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I've heard the term, "Granny Gas" here in Canada for years...
I guess it would translate to something like, "Plus a pinch for Gram" in Limey speak?
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Old 25th Apr 2013, 04:16
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I would guess granny fuel would get you busted on a ramp check if it put you over max takeoff wt. Good luck.
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Old 25th Apr 2013, 04:22
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Granny fuel because dispatch cut you short of your comfort fuel sounds fine. personally, I just called them and told them what I needed.
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Old 25th Apr 2013, 06:53
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Originally Posted by john smith
There is no 'new' fuel figure. We dial up 100kg extra, which usually gives us the fuel we asked for in the first place
- I misunderstood you - I thought you were discussing 'granny fuel' on this thread. In which case there is no "0.1 tonnes" to worry about since you wanted 7 and got 7? Non-event!
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Old 25th Apr 2013, 08:26
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Folks,
A comment on gauge/totaliser accuracy, in part the story is covered in the changes to certification standards over the years ---- showing the development of sensible thinking over the years --- as a result of hard won and usually deadly experience.

Also the development of the concept of fixed final reserve, which is not 30m holding, but the amount of fuel, calculated or indicated, that is to take care of all the inaccuracies in fuel measurement, so that the engines are running at touchdown ---- the Boeing equivalent is minimum fuel for approach.

No gauge or totaliser system in "accurate", all measuring systems have an order of accuracy.

"Granny fuel", that I know as a "quick squirt for mum and the kids" is relatively common for small aircraft.

Airline fueling practices should be far more exacting --- including adding extra fuel when the discrepancy between calculated fuel on board, and indicated fuel on board (including having used the corrected SG--- as in correcting the average SG to account for fuel on board SG v SG of fuel loaded) exceeds 3% --- and in the case when there is a serious mismatch, drip the tanks.

And what goes on the loadsheet ---- the minimum fuel that you know you actually have on board.

Tootle pip!!
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Old 25th Apr 2013, 09:09
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I can even have a guess who the Captain is.

Its not common to call it granny fuel.

19 seaters are in the main under 7500kg So we are not talking 200kg extra I would hope. Maybe 50kg which is 10mins extra.

Some round up to the next 50ltrs of fuel. Some use 0.77 SP when ordering and some round down the arrival fuel.

Its all OK until you have an engine failure in LVP's and you can't look out the window and see and avoid. These machines are in general getting on for 20 odd years old and they weren't very spritely climbing on one engine when new.

Also another thing to take a look at is the drift down which is surprisingly low at max weight. So you may have issues with reaching MSA if you have already got 18 blokes on-board who last saw 86kg in there teens.

Personally I just don't, I check the MPI's to make sure they are the same as the gauges and then fill up to the required amount. No more no less.

But there are more than a few out there, that to be honest are correct reckon that your more likely to have issues due to low fuel than an engine failure when flying a route at min fuel and Max load. An extra 50kg isn't so bad its when they start going 100's of kg over weight or in LVP conditions it seems a bit crazy to me.
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Old 25th Apr 2013, 10:59
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As has been alluded to by previous posters, fuel density variation can be significant,
Ihave dropped 1500 imperial gallons of petrol into an underground tank, the diprodshowed 1530 Gal........12 hours later, it's at the correct .1500.
Diesel/Kero is pumped and metered, without density-correction, you get less WEIGHT of fuel on a warm day, than a cold one, if metering is by volume.
I find the use of "mixed units" (Kg / Lbs / Litres /Imp. Gals. / US Gals. ) quite disturbing....do the Bowsers have load-cells and deliver WEIGHT ? or metering-pumps and deliver by VOLUME ?

ISTR the Gimli incident was caused by just this "scrambled thinking"

Weight is, of course, the crucial issue with a small aircraft.
The arbitrary "nominal" weights used on a Pax. airliner probably give a wider variance of true load than the fuel density variation.
so, all pretty hypothetical, really, as far as big jets are concerned.

When it's a choice of fuel /luggage/a soul to keep within W&B limitations, that's a different kettle of fish!
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Old 25th Apr 2013, 12:25
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Bowser delivers volume. Converted to Weight with reference to S.G.
Can be significant on a large uplift. In the OP's case I don't know. Do smaller a/c use a standard SG like large short haul a/c?


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Old 25th Apr 2013, 12:54
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Large uplift they use less than the big boys do taxing.

Max fuel is between 1200kg and 1500kg and its not uncommon to start off with less that 800kg.

They burn about 6kg a min.

As for the S.G this can a problem even if you get given one by the bowser man. The S.G tends to get taken early morning. And you have a special bowser that can do over wing fueling. So it can sit out in the sun all day until you refuel. Which is why a lot of us use an SG of 0.77 when ordering. A 500-1000trs is the normal uplift at a time so its won't give you that much extra over. Most of the modern TP's have pressure refuelling and the units I have used anyway pull 50-75kg of it initially which calibrates the S.G. before pulling up to the weight in the panel. And a cross check against the bowser S.G. is usually within 0.01 which would be normal for a bulk to bowser temp rise.
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Old 26th Apr 2013, 01:20
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Its all OK until you have an engine failure in LVP's and you can't look out the window and see and avoid. These machines are in general getting on for 20 odd years old and they weren't very spritely climbing on one engine when new.
Yup. These planes don't achieve the published cruise performance either.

An extra 50kg isn't so bad
As long as you don't take 50 kg of cargo/pax with you.

As for the S.G this can a problem even if you get given one by the bowser man. The S.G tends to get taken early morning. And you have a special bowser that can do over wing fueling. So it can sit out in the sun all day until you refuel. Which is why a lot of us use an SG of 0.77 when ordering. A 500-1000trs is the normal uplift at a time so its won't give you that much extra over. Most of the modern TP's have pressure refuelling and the units I have used anyway pull 50-75kg of it initially which calibrates the S.G. before pulling up to the weight in the panel. And a cross check against the bowser S.G. is usually within 0.01 which would be normal for a bulk to bowser temp rise.
This doesn't happen where I'm from. When I call in for fuel I ask for the "batch corrected density". That is the density of the batch in the fuel truck which is corrected to 15 degrees C. The truck also meters at 15 degrees C. Today the batch corrected density was 0.819 kg/litre - which means that if you have a litre of jet fuel and the temperature of it is 15 degrees C, its mass will be 0.819 kg. That will not change as long as nothing is added or subtracted from the fuel truck - temperature does not affect this number! So if I want 500 kg of fuel I take 500 and multiply by 0.819 to get 409.5 litres. If the fuel temp is 15 degrees C then the actual volume pumped into the tanks will be 409.5 litres. If the fuel temp is greater than 15 then the volume pumped in will be greater, and if the fuel temp is less than 15 then the volume pumped in will be lesser. Whatever the case, I know that I will get 500 kg of fuel. I can use 0.819 throughout the entire day as long as the fuel is coming from the same truck.
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Old 26th Apr 2013, 10:08
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There are a few Accident reports of 19 seaters which have come to grief.

I won't post the direct links to them in case it gets the operators backs up that I am implying that they operate overweight. Which I can't be bothered dealing with.

But I am sure with out much searching you can find them. It may not be the flight in question which causes the issue. It maybe 50-100 sectors later that issues occur.
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Old 26th Apr 2013, 10:21
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Virtus,

Check your calculations...Kerosine is lighter than water...you need to multiply by around 0.8 to get from litres to Kg....
An extra 100 or so is ok, it will not change anything on a medium Jet. The gauges are less accurate than that.
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Old 26th Apr 2013, 10:40
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An extra 100kg is min an extra 5% of your traffic load on these old heaps.
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Old 26th Apr 2013, 10:43
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Granny Fuel:

Fill mains to full. Plane sits on ramp, fuel expands and spills over into aux tanks = Granny fuel.
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Old 26th Apr 2013, 13:36
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that's a huge like OK465
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Old 26th Apr 2013, 13:50
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These days that in itself could be worth 100 kg.
- you saying they employ grannies??
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Old 26th Apr 2013, 13:52
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We prefer the term GILF's

But you might term young totty

Last edited by mad_jock; 26th Apr 2013 at 13:53.
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