Fuel Quantity Indication System and Fuel Policy

Sébastien SELLEM

Flight Safety Director -Accident/incident Investigator- Type Rated ATR Pilot

The ATR fleet has encountered events associated with erroneous fuel quantity indication.

The fuel quantity indicating system informs the crew of the quantity of fuel available in each tank during the flight using 5 (ATR42) or 6 (ATR72) probes per wing tank.

The accuracy on the total fuel indication, on ground, with an attitude within -3° and +1° of pitch and ±2° of roll is:

±1 % of full scale near zero level
±3 % of full scale at full level

For all other ground and flight conditions, outside this envelope (pitch and roll) accuracy of fuel indications will be degraded.

By European regulation (CAT.OP.MPA.260), the captain is responsible to verify before each flight that the aircraft carries at least the planned amount of usable fuel to complete the flight safely, considering the expected operating conditions.

By European regulation (CAT.OP.MPA.150), the operator shall establish a fuel policy to ensure that every flight carries sufficient fuel for the planned operation.

The following procedure is the expected actions that should be taken by the crew.

Compute PLAN UPLIFT

Compare fuel tanker receipt with the planned UPLIFT

1- FLIGHT PLAN: The captain requires 3 000 kg to the Fuel Tanker based on the minimum fuel block from the flight plan (FPL).

2– TECH LOG: The captain verifies the fuel remaining recorded in the tech log & FQI.

3– PLAN UPLIFT: The captain will compute the plan uplift. It means a substraction between the mini fuel block and the remaining fuel recorded in the technical logbook.

In this example: 3000kg – 1150kg = 1850 kg

4– ACTUAL UPLIFT: The fuel tanker receipt will provide you the volume of fuel delivered in liters (or Gallons). This value must be converted into KG (or LBS) based on the fuel density. (FCOM PRO.NOP.NSU.28).

If delta between plan uplift and actual uplift is greater than ±3 % of full scale at full level (ATR72/42), the total fuel uplift is in excess of the FQI tolerance, hence not acceptable. (SD ATR-A-28-42-XX-01001-04CA-A).

5– FQI – FUEL QUANTITY INDICATION: The crew verify that the FQI indicates the correct value compare to the flight plan.

6– FUEL USED: the crew notes the fuel used after the flight.

7– FUEL REMAINING: The crew computes the fuel remaining (3000 kg – 560 kg = 2440 kg) and compare the value with the FQI (≈2440 kg).

If delta between remaining fuel and FQI is greater than ±3 % of full scale at full level (ATR72/42), contact the maintenance.

3.1. Magnetic level indicator

In case of quantity indicating system troubleshooting, on ground, two magnetic level indicators in each tank through the lower wing skin give fuel quantity. Tables provide fuel mass with corrections established for aircraft attitude and fuel density. The accuracy of the magnetic level indicators is ±200 liters/tank and does not consider the fuel density. (FCOM.NOP.NSU.28 FUEL)

3.2. Fuel probe

The probes have different lengths and forms according to their location in the tank. The fuel level is measured by making the difference between capacitance measured in the fuel and the empty capacitance (capacitance measured in the open air (without fuel)). Each probe has its own empty capacitance with a tolerance. The fuel quantity in a tank is measured by summing the probes capacitances in the fuel and subtracting the total empty capacitance.

If one probe is inaccurate, leading to an erroneous capacitance value, it will impact the full capacitance measured by the FQI, thus the fuel quantity indicated for the associated tank. In some case, a default on one probe, could lead to an overestimation or underestimation meaning that the FQI will display a value higher or lower than the actual fuel.

Maintenance: MP ATR-A-28-42-70-01001-340A-A (Functional Test of the Fuel-Tank Quantity Probe) to check the correct operation of probes.

3.3. Harness connected to the associated probe

An issue on the connector could lead to lose the capacitance of the probe given by the line of the harness. An issue on the harness (cable shield), could lead to an overestimation or underestimation meaning that the FQI will display a value higher or lower than the actual fuel.

Maintenance: MP ATR-A-28-42-70-01001-340A-A (Functional Test of the Fuel-Tank Quantity Probe) to check the correct operation of harnesses.

3.4. Temperature probe

An issue on the temperature probe located in the feeder tank could create a deviation on the computed fuel density and so on the fuel quantity indication.

Maintenance: Check the resistance of the Compensator Resistance as per CMM 28-42-72.

3.5. Pollution

Pollution as water or contamination of the fuel could also create an error on the FQI.

Maintenance: MP ATR-A-12-32-28-00001-377A-A (fuel – sampling for analysis) and MP ATR-A-28-11-XX-00001-263A-A (Biocide Treatment of the Fuel Tanks) if contamination is found.

3.6. Fuel flow

The fuel flow is used to compute the Fuel Used and could create an error on the remaining fuel.

Maintenance: AFI ATR-A-73-31-XX-02002-421A-A (Engine Fuel and Control – Fuel Flow System Fault).

3.7. Additional information

If needed dispatch under MMEL ITEM 28-42-01 FUEL QTY INDICATION

For further information:

FCOM.DSC.28 FUEL
FCOM.NOP.NSU.28 FUEL:
- QUANTITY INDICATION
- USE OF MANUAL (MAGNETIC) INDICATORS
- CONVERSION QUANTITY-WEIGHT

a) ATR42/72-600 Version

**FUEL LO LVL**
CONDITION	VISUAL	AURAL
Fuel quantity indication below 160kg (352lb) – OR- Feeder tank not full	– MC light flashing amber – FUEL LO LVL amber message on EWD – Associated tank LO LVL amber message on Engine SD page – Feeder tank is amber with fuel quantity in amber on MFD (level between 160kg and 50kg) or in red reverse video (level below 50kg)	SC

**FUEL MISMATCH**
CONDITION	VISUAL	AURAL
Difference between fuel quantity computed by FMS and fuel quantities processed by the FCU is greater than 200kg (440lb) during more than 10s (on ground) or 60s (in flight)	– MC light flashing amber – FUEL MISMATCH amber message on EWD	SC

**FUEL UNBALANCED**
CONDITION	VISUAL	AURAL
Discrepancy greater than 200kg (440lb) between left and right tanks fuel quantities	– MC light flashing amber – FUEL UNBALANCED amber message on EWD	SC

b) ATR42/72 with the secondary fuel low level (Feeder tank not full)

CONDITION	VISUAL	AURAL
Fuel quantity indication below 160kg (352lb) – OR- Feeder tank not full	– MC light flashing amber – FUEL amber message on CAP – LO LVL amber light on FUEL QTY indicator	SC

c) ATR42/72 without the secondary fuel low level (Feeder tank not full)

CONDITION	VISUAL	AURAL
Fuel quantity indication below 160kg (352lb)	– MC light flashing amber – FUEL amber message on CAP – LO LVL amber light on FUEL QTY indicator	SC

Pilot should always compute and compare the information from the fuel quantity indicator, the fuel tanker receipt and the fuel used.

ATR recommends each operator establishes a fuel policy in their daily flight operations in accordance with their regulation (European regulation CAT.OP.MPA.260 and CAT.OP.MPA.150).

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