AIRBUS OPERATING PROCEDURES 8.3.
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POLICY MANUAL In-flight fuel management Page 1
Content
8.3.7. POLICY AND PROCEDURES FOR THE IN-FLIGHT FUEL MANAGEMENT.1
8.3.7.1. FUEL QUANTITY CHECKS......................................................................2
8.3.7.1.1. General...............................................................................................2
8.3.7.1.2. In-flight fuel checks.............................................................................2
8.3.7.1.3. In-flight fuel management. ..................................................................3
8.3.7.1.4. Required minimum remaining fuel ......................................................4
8.3.7.1.5. Re-planning in flight............................................................................4
8.3.7.1.6. Minimum fuel operation ......................................................................4
8.3.7.2. FUEL FREEZING LIMITATIONS ..............................................................5
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8.3.7. POLICY AND PROCEDURES FOR THE IN-FLIGHT FUEL MANAGEMENT
8.3.7.1. FUEL QUANTITY CHECKS (JAR-OPS 1.350 / 1.375)
8.3.7.1.1. General
The fuel on board when starting the engines must not be less than the minimum fuel
quantity defined by the fuel policy. Refer to 8.1.7.1.
The fuel on board must be periodically checked in flight to determine if the remaining
fuel is not less than the minimum fuel required to continue the intended flight. This will
help the Commander to detect possible fuel consumption higher than anticipated or a
fuel leak.
8.3.7.1.2. In-flight fuel checks
The remaining fuel must be recorded and evaluated to:
• Compare actual consumption with planned consumption;
• Check that the remaining fuel is sufficient to complete the flight; and
• Determine the expected fuel remaining on arrival at the destination.
In-flight fuel monitoring is made using the operational flight plan.
The crew must carry out regular fuel checks (at waypoints and at least every 30
minutes) noting:
• Time of observation
• Fuel used (FU)
• Remaining fuel on board (FOB)
• Fuel flow (FF)
Subtract "Fuel used" from the block fuel (recorded before engine start) and compare
this figure with the "Remaining fuel on board". If there is no major discrepancy, the
figures read on the aircraft should be used.
This type of monitoring would detect fuel leaks and provide a more reliable basis of
calculation in case of either Fuel Quantity Indicator (FQI) or Fuel Used (FU) failure
during flight.
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However, without any failure or fuel leak, some discrepancies, which may be
considered large (more than 1000 kg on some aircraft), can be evidenced. There may
be due to:
- APU consumption (up to 150 kg/h) which is not recorded by FU
- FQI errors on block fuel and on FOB
- FU indication tolerance
Water freezing in the tanks may also affect the FQI indications.
8.3.7.1.3. In-flight fuel management.
The commander shall ensure that the amount of usable fuel remaining in flight is not
less than the fuel required to proceed to an aerodrome where a safe landing can be
made, with final reserve fuel remaining.
If, as a result of an in-flight fuel check, the expected fuel remaining on arrival at the
destination is less than the required alternate fuel plus final reserve fuel, the
Commander must take into account the traffic and the operational conditions prevailing
at the destination aerodrome, along the diversion route to an alternate aerodrome and
at the destination alternate aerodrome, when deciding whether to proceed to the
destination aerodrome or to divert, so as to land with not less than final reserve fuel.
• On a flight to an isolated aerodrome
The last possible point of diversion to any available en-route alternate aerodrome shall
be determined.
Before reaching this point, the commander shall assess the fuel expected to remain
overhead the isolated aerodrome, the weather conditions, and the traffic and
operational conditions prevailing at the isolated aerodrome and at any of the en-route
aerodromes before deciding whether to proceed to the isolated aerodrome or to divert
to an en-route aerodrome.
When approaching the last possible point of diversion to an available en-route
aerodrome, unless the fuel expected to remain overhead the isolated aerodrome is at
least equal to the additional fuel calculated as being required for the flight, or unless
two separate runways are available at the isolated aerodrome and the expected
weather conditions at that aerodrome comply with those specified for planning minima
for isolated destination aerodromes (refer to 8.1.2.2.3), the Commander should not
proceed to the isolated aerodrome.
In such circumstances, the Commander should instead proceed to the en-route
alternate unless according to information he has at that time, such a diversion appears
inadvisable.
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8.3.7.1.4. Required minimum remaining fuel
The minimum fuel expected to be available on arrival at the destination aerodrome is
the sum of the alternate fuel and the final reserve fuel as defined in chapter 8.1.7.1.1.
If it appears en route that the fuel remaining is such that the fuel at destination will be
less than expected above, the Commander should consider the following:
- Decrease aircraft speed (down to Max Range Speed / Cost Index minimum)
- Obtain a more direct route
- Fly closer to the optimum FL (taking the wind into account)
- Select a closer alternate aerodrome
- Land and refuel
8.3.7.1.5. Re-planning in flight
Re-planning in flight may be done when planned operating conditions have change or
other reasons make further adherence to the original flight plan unacceptable or
impractical, for example:
- Bad weather conditions or runway condition at the planned destination and
alternate.
- Fuel penalties due to ATC constraints or unfavourable wind.
- Degraded aircraft performance
8.3.7.1.6. Minimum fuel operation
Advise ATC when the remaining fuel has reached a state where, upon reaching
destination any undue delay cannot be accepted.
This is not an emergency situation but just an advisory that indicates an emergency
situation is possible should any undue delay occur.
A minimum fuel advisory does not imply a need for traffic priority.
If the remaining usable fuel suggests the need for traffic priority to ensure a safe
landing an emergency should be declared and report fuel remaining in minutes.
An emergency exists if the fuel remaining in flight is less than the final reserve fuel (30
minutes holding).
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8.3.7.2. FUEL FREEZING LIMITATIONS
The minimum fuel temperature, published in the operational documentation, may be more
restrictive than the certified aircraft environmental envelope. It includes two different
limitations both linked to engine operation: Fuel freezing point limitation, and fuel heat
management system limitation.
(a) Fuel freezing point limitation
This limitation provides an operating margin to prohibit operations under fuel
temperature conditions that could result in the precipitation of waxy products in the
fuel. The resulting limitation varies with the freezing point of the fuel being used.
Aside from this, engines have a fuel warming (oil cooling) system at their inlet.
Because of the architecture of this system and the fact that the fuel inlet hardware
varies from one engine type to another, the specification of what fuel temperature is
acceptable at the inlet of the engine varies from one engine type to the other.
Therefore, engine manufacturers sometime require a temperature margin to fuel
freezing point to guarantee correct operation.
The engine manufacturer’s margins relative to the fuel freezing point are as follows:
- Pratt and Whitney : 0°C
- Rolls Royce : 0°C
- General Electric : 3°C
- IAE : 4°C
- CFM (A319/A320/A321) : 4°C
- CFM (A340) : 5°C
(b) Fuel heat management system limitation
This limitation reflects the engine capability to warm-up a given water-saturated fuel
flow to such a point that no accumulation of ice crystals may clog the fuel filter.
Such a limitation does not appear in the documentation for some engine types when
outside the environmental envelope.
When applicable (refer to FCOM Fuel limitations) the resulting limitation is a fixed
temperature below which, flight (or takeoff only, if high fuel flows only cannot be
warmed-up enough) is not permitted.
The most restrictive of the two limitations above (a) and (b) should be considered.
Note: The fuel anti-icing additives authorised by engine manufacturers decrease the
freezing temperature of the water contained in the fuel (decrease the fuel heat
management system temperature limitation), but have no effect on the fuel freezing
temperature itself.
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Furthermore, an additional 2°C margin for temperature indication inaccuracy has been
requested by airworthiness authorities for A300/A310/A300-600 aircraft.
Therefore, the minimum fuel temperature should be:
FUEL FREEZING POINT
+ ENGINE MANUFACTURER MARGIN
(+ 2°C for A300/A310/A300-600)
The fuel freezing point to be considered is the actual fuel freezing point. (Refer to
8.2.1.3.2. - Fuel freezing point determination)
If the actual freezing point of the fuel being used is unknown, the minimum fuel
specification values as indicated below should be used as authorised by the AFM/FCOM.
JET A JP5 JET A1/JP8 RT/TS-1 JET B TH JP4
-40°C -46°C -47°C -50°C -50°C -53°C -58°C
The procedures dealing with low fuel temperature vary with the aircraft type. Refer to
FCOM.
Whenever necessary the TAT has to be increased. This is achieved by an aircraft speed
increase and/or an altitude decrease.
Increasing the aircraft speed provides a marginal TAT increase (in the order of 0.5 to 1°C
for 0.01 M increase) and thus a small fuel temperature increase, at the expense of a
significant increase in fuel consumption.
Decreasing the altitude generally provides a SAT increase (about 2°C per 1000ft).
Nevertheless, whenever the tropopause is substantially low, decreasing the altitude may
not provide the corresponding expected SAT and, thus, TAT increase.
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