Fuel on Board Difference Calculation

[pwned]

I can't remember the formula for calculating the discrepancy. Can someone help plz?

Is it - Difference/total shown on fuel gauge x 100= %

Or Difference/ (truck uplift+ fuel before refuelling) x 100= % ? or both method wrong?

Our company allows 3% difference. But i forgot how to do it.:O

Thank you in advance.

[Checkboard]

Not an "official source", but:

http://www.b737.org.uk/fuel.htm#Fuel_Gauges

The total tolerance for the FQIS system is based on a full tank. For example, if the fuel tank maximum capacity is 10,000 KG, then the tolerance of the gauging is 0.03 (airplane with analog indicators) * 10000 = 300 KG. The system tolerance is then +/- 300 KG at any fuel level within the tank.

[BOAC]

+/- 3% of calculated uplift

[AerocatS2A]

Our company allows 3% of the higher number. Best way to work it out is to multiply the higher figure by .97, if the result is less than the other figure, you're good to go.

Example:

Fuel from truck plus fuel remaining from previous flight = 10,000 lbs

Fuel on gauges = 9,800 lbs

10,000 x 0.97 = 9,700 lbs

9,800 is more than 9,700 therefore 9,800 is within 3% of 10,000 and the fuel check is ok.

Multiplying by 0.97 is the same as taking 3% off, it gives you the lower limit of the 3% check. If you need to do it the other way, multiply by 1.03 that finds the upper limit of the 3% check, however if your rule is like ours, within 3% of the higher figure then you would always multiply the higher figure by 0.97 not the lower figure by 1.03.

If your rule is like BOAC's, multiply the calculated uplift by either 0.97 or 1.03 as appropriate depending on whether the gauge figure is higher or lower than the calculated figure.

[pwned]

Called a friend he said what he does is

Eg,
A) Difference( between Bowser Uplift - Calculated uplift ) divided by Bowser uplift x 100?

Eg, Bowser uplift is 10, 000 kgs. Gauges showing total before refuel- 5000. After refuel total shows 15 400kgs. So Calculated uplift= 10400kgs.

Difference= 400 kgs between Bowser uplift ( 10000kgs) and Calculated uplift(15400kgs -5000kgs= 10400 kgs ) using the fuel gauges.

So discrepancy--> 400kgs/10000kgs x100= 4%?

And i can't remember where i read now, the moethod used was

B) Eg, Bowser uplift= 10000kgs. Gauges uplift ( as above ) 10400kgs. Difference= 400kgs.

So discrepancy --> 400kgs divided by total fuel on board which is 10000kgs +5000kgs x100.= 400/15000 x100=2.7%

So, which is the correct way? Thanks. i know it seems simple...but its between a dripstick check ( 4%)--> long delays or a non event( 2.7%). Company tolerance is 3%. So it would be nice if i know the absolute correct method.
Thank you once again.

[AerocatS2A]

Your ops manual should specify whether the check is against total fuel on board (B) or just the uplifted amount (A). Our company uses method B.

I'm not about to say that YOU should use method B because it may be company specific.

[pwned]

I think you are right Aerocat. I have a feeling its FOB. Just need to find the reference now. Thanks once again :).

[BOAC]

Well, pw - I hope the message is clear? Company specific, so
1) Company Ops Manual (assuming you have one) - if not
2) ask your company - if not.................................

Cannot see why you are asking here?

[pwned]

Word.


Thanks:)

[Amhplus]

Use the app called AmhFuel from play store or AppStore to calculate discrepancy in seconds.

[Tom Sawyer]

Your ops manual should specify whether the check is against total fuel on board (B) or just the uplifted amount (A). Our company uses method B.

I'm not about to say that YOU should use method B because it may be company specific.

I can confirm this.....I deal with 7-8 airlines as an Engineer, and all of them have different ideas of how to do the calculation and method in the Tech Log.

[Black Pudding]

Example

Airbus A320 has 4000kgs showing on board before fuelling

Required fuel for departure 13,000kgs

13,000 x 4000 equals 9000 kgs estimated uplift from refuelling vehicle.

Ask refuelling company for the correct SG of the fuel supplied.

For example if SG is 0.789 then the estimated calculated uplift should be 11,407 litres.

Once refuelled, whatever the litres is, convert back to KGs and the difference is the discrepancy.

For example, if the actual refuel is 11,700 litres, that equates to 9231 kgs, a discrepancy of 231 kgs more needed to give you your 9000 kgs extra, meaning your fuel gauges are under reading. I’d say if they are over reading, then that’s more of a problem.

The whole point of working out calculated and comparing to actual is that you are taking the opportunity to use fuel providers calibrated metres to make sure your aircraft gauges are reading correctly.

Your aircraft manufacturer should have tables with maximum discrepancies allowed for certain amounts of uplift or fuel on board before a mandatory fuel tank stick check is required.

The above is only my thoughts an opinions. I was an aircraft refueller for Shell in the UK for 9 years before Commercial Pilot.

[oceancrosser]

Use the app called AmhFuel from play store or AppStore to calculate discrepancy in seconds.
Really need an app for that?

[Private jet]

The whole point of working out calculated and comparing to actual is that you are taking the opportunity to use fuel providers calibrated metres to make sure your aircraft gauges are reading correctly. .

This ^^^^^^^

Required fuel - Fuel on board = Required uplift weight.
After refuelling; volume delivered (from refuellers receipt) x SG = uplift weight
uplift weight / required uplift weight = discrepancy. (1.03 = + 3%)

Different operators have different procedures but the result is the same. (the important bit is the ratio of actual uplift to calculated uplift)

[HOVIS]

Use the app called AmhFuel from play store or AppStore to calculate discrepancy in seconds.
Only if it is approved for use by your employer, aircraft manufacture, the airline you are refuelling etc. There is a Boeing approved app for the 777. Especially useful when doing a stick check.

[HOVIS]

I can confirm this.....I deal with 7-8 airlines as an Engineer, and all of them have different ideas of how to do the calculation and method in the Tech Log.
Indeed, and one has to use the one approved by the airline. The FCOM usually has tables, graphs etc to explain it in detail. The AMM will also show the method that should be used.