Airbus Fuel Accuracy

Fuel accuracyFuel accuracy

Operational Liaison Meeting FBW aircraft

Fuel accuracyFuel accuracy 2

ContentContent

Introduction

What systems to determine Fuel quantity in the aircraft?Fuel Quantity Indicator (FQI) SystemManual Magnetic Indicators (MMI)

Why Fuel quantity discrepancies:On ground?In flight?

Conclusion


FQI System descriptionFQI System description

The FQI system is a computerized system that measure:

the total fuel massthe total fuel volumefuel quantity in each tank

Fuel Volume and mass are determined usingFuel probes (capacitance is proportional to fuel level)densitometers



Example of Probeslocation in anA320 aircraft



Fuel Quantities are displayed on the ECAM

A320 A330



Fuel Quantities are displayed on the ECAM

A320

FQI is inaccurate


Manual magnetic IndicatorsManual magnetic Indicators

MMIs are installed in each wing tanks.Each tank’s fuel quantity on ground can be determined:

reading the MMI dipstick numberreading the aircraft attitude (grid square letter and number)using the MMI table

A320 MMI

1

Wing Tanks MMI Table (Liters)


ContentContent

Introduction



Conclusion


Why Fuel Quantity discrepancies on ground?Why Fuel Quantity discrepancies on ground?

At the end of refueling, discrepancies reported between:

uplifted quantity measured by the bowsers

uplifted quantity measured using FQI

Those discrepancies may be due to:

Bowser quantity and density error

APU fuel used

FQI accuracy



Bowser quantity and density tolerances:Volume tolerance: generally less than 0.5% of fuel upliftedDensity tolerance (both temperature accuracy and density reading error): 0.25% of fuel upliftedTotal bowser tolerance: 0.75% of fuel uplifted

APU fuel used:To be taken into account when comparing FOB pre-refuel and FOB post-refueldepends on external condition and generator loadAPU fuel consumption: between 100 and 150Kg/h



The FQI is a gauging system.

Bias and tolerances can affect FQI system accuracy:tank manufacturing tolerancesFQI computer inaccuraciestolerances in density determinationwater that causes FQI over-readswing deflection


FQI accuracy on groundFQI accuracy on ground

Single Aisle Aircraft

Long Range Aircraft:

FOB OVERREAD UNDERREAD0 to 0.5% Max FOB 00.5%Max FOB to Max FOB 1% FOB

- (0.5% Max FOB +0.5% FOB)

FOB OVERREAD UNDERREADBelow 2% Max FOB Decrease linearly to 0 Decrease linearly to -1% Max FOB2% Max FOB to Max FOB +(0.5% Max FOB +0.5% FOB) - (0.5% Max FOB +0.5% FOB)


FQI accuracy on groundFQI accuracy on ground




- (0.5% Max FOB +0.5% FOB)

FOB OVERREAD UNDERREADBelow 2% Max FOB Decrease linearly to 0 Decrease linearly to -1% Max FOB2% Max FOB to Max FOB +(0.5% Max FOB +0.5% FOB) - (0.5% Max FOB +0.5% FOB)

FAR/JAR 25.1337: Each fuel quantity indicator shall be calibrated to read “zero” during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply


Why Fuel Quantity discrepancies on ground?Why Fuel Quantity discrepancies on ground?Single Aisle FQI Accuracy (GROUND) MAX FOB= 19T

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0 2 4 6 8 10 12 14 16 18 20

Actual FOB Tonnes

FQI T

OLE

RAN

CE

Tonn

es


Why Fuel Quantity discrepancies on ground?Why Fuel Quantity discrepancies on ground?LONG RANGE FQI ACCURACY (GROUND) MAX FOB=113T

-1.5

-1

-0.5

0

0.5

1

1.5

0 20 40 60 80 100 120

Actual FOB Tonnes

FQI

TOLE

RANC

E To

nnes



Max discrepancy =Max [Fuel load(per bowser)- Fuel added on ECAM (FQI end-FQI start)]=

[±Bowser dev ± FQI dev(end) ± FQI dev(start) +APU fuel (refuel)]



EXEMPLE: (A320-200)ACTUAL FOB before refueling: 3TACTUAL FOB after refueling: 18TMax TOTAL Bowser inaccuracy : 115kgAPU Fuel used for 30minutes 50kgMax FQI deviation* 220kg

______ TOTAL: 385kg

The FQI deviation is only significant when FQI Over/ Under-readings before and after refueling are very different



-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0 2 4 6 8 10 12 14 16 18 20

Actual FOB Tonnes

FQI T

OLE

RAN

CE

Tonn

es

MAX FQI deviation

during refueling


Why Fuel Quantity discrepancies on ground?Why Fuel Quantity discrepancies on ground?LONG RANGE FQI ACCURACY (GROUND) MAX FOB=113T

-1.5

-1

-0.5

0

0.5

1

1.5

0 20 40 60 80 100 120

Actual FOB Tonnes

FQI

TOLE

RANC

E To

nnes



What about MMI use?

MMI accuracy: +/-5% FOB



-1.5

-1

-0.5

0

0.5

1

1.5

0 2 4 6 8 10 12 14 16 18 20

Actual FOB Tonnes

FQI/M

MI T

OLE

RAN

CE

Tonn

es

FQIMMI


Why Fuel Quantity discrepancies on ground?Why Fuel Quantity discrepancies on ground?LONG RANGE FQI ACCURACY (FLIGHT) MAX FOB=113T

-8

-6

-4

-2

0

2

4

6

8

0 20 40 60 80 100 120

Actual FOB Tonnes

FQI/M

MI T

OLE

RANC

E To

nnes

FQI

MMI



What about MMI use?

MMI accuracy: +/-5% FOB

Do not use MMI to check FQI system

Only use MMI when FQI is inoperative


ContentContent

Introduction



Conclusion


Why Fuel Quantity discrepancies in flight?Why Fuel Quantity discrepancies in flight?



When performing this check, discrepancies come from:

BLOCK FUEL accuracy

FU accuracy

FOB accuracy


FU accuracyFU accuracy

FU is the integration of the Fuel Flow over time

The accuracy of the Fuel Flow meter depends on:Fuel flow rate

Temperature conditions

But, keep in mind that the FU indicationdoes not take into account APU fuel

consumption


FU accuracyFU accuracy

FU accuracy:

Estimated to be better than +/-1.5%

For normal Cruise conditions ~+/-1%


FU accuracy on long Range AircraftFU accuracy on long Range AircraftMaximum F.USED Deviation

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50 60 70 80 90 100 110

FOB tonnes

Dev

iatio

n to

nnes

F.USED 31 tonnes F.USED 67 tonnes F.USED 103 tonnes


FQI accuracy in flightFQI accuracy in flight




- (1% Max FOB +0.5% FOB)

FOB OVERREAD UNDERREADBelow 2% Max FOB Decrease linearly to 0 Decrease linearly to –0.64% Max

FOB2% Max FOB to Max FOB +(0.3% Max FOB +0.95%FOB) - (0.3% Max FOB +0.95% FOB)


Why Fuel Quantity discrepancies in flight?Why Fuel Quantity discrepancies in flight?Single Aisle FQI Accuracy (Flight) MAX FOB= 19T

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 2 4 6 8 10 12 14 16 18 20

Actual FOB Tonnes

FQI T

OLE

RANC

E To

nnes


Why Fuel Quantity discrepancies in flight?Why Fuel Quantity discrepancies in flight?LONG RANGE FQI ACCURACY (FLIGHT) MAX FOB=113T

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 20 40 60 80 100 120

Actual FOB Tonnes

FQI T

OLE

RANC

E To

nnes



The maximum theoretical Combined FOB and FU deviation in indication is possible when:

At departure the FQI system has the maximum deviation (positive or negative)

At time X, the FQI system has the maximum deviation, but with the opposite sign to the FQI at departure, and the F. USED deviation moves in the same sense



EXEMPLES:

A340 aircraft which takes off with 113 Tons on board. Fuel check with 10 Tons on board:MAX Theoretical Combined FOB and FU deviation:

2.554 TonsA340 aircraft which takes off with 41 Tons on board.Fuel check with 10 Tons on board:MAX Theoretical Combined FOB and FU deviation:

1.749 Tons

Comparing FOB departure-FOB+FU is a good practice !


ConclusionConclusion

Your FQI system has a good accuracy

On ground, only use MMI when FQI is inoperative

In flight, continue to perform the FOB check, being confident on the Fuel Quantity Indications displayed on ECAM

Airbus Fuel Accuracy

Documents

Transcript of Airbus Fuel Accuracy