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Monitoring Fuel and Policy Fuel 2
Figure 2.4 Insufficient fuel
A check of the aircraft’s fuel system may be required if it was thought that the excess consumption was caused by a fuel leak or a fuel-gauge fault. An error in computation at flight planning or in the actual fuel amount up-lifted at departure may have been the cause of the shortfall. Aircraft have run short of fuel. Very strong un-forecast headwinds have been encountered. Pounds to kilograms, kilograms to pounds, have been erroneously converted and specific gravities applied incorrectly!
Special Cases 1 – Decision Point Procedure
There is a special case when we may get airborne without sufficient contingency fuel for the planned trip to the destination. This is called decision point procedure.
Decision Point Procedure - ATypical Scenario
Consider the ‘Howgozit’ in Figure 2.6. A flight from Oxford to Faro, in southern Portugal, is planned. There are alternates near Faro - Seville or Jerez, for instance. The total of the final reserve fuel and the alternate fuel is 3000 kg. The trip fuel is exactly 10 000 kg. There is a suitable en route diversion at Lisbon, so contingency fuel is 3%, which comes to 300 kg. This means that we need 13 300 kg at take-off.
Unfortunately, the maximum capacity of our fuel tanks means that we can get in only 13 150 kg at take-off. This is 150 kg short of the minimum requirement. Does this mean that we cannot do this flight? Not necessarily, if there is a suitable en route alternate.
We define the top of descent for going into Lisbon, our alternate, as the Decision Point. We have plenty of fuel to proceed to Lisbon, so this is legal. At this Decision Point, we carry out a fuel check. Unless unforeseen circumstances have arisen, we will probably not have used the contingency fuel and so will still have 150 kg above the expected consumption line for Faro.
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The requirement for contingency fuel is 3% above the trip fuel required for the remainder of the flight, not the start trip fuel. At this stage of the trip, the required contingency fuel is only 55 kg. If the fuel remaining includes this 55 kg contingency fuel plus the remainder of the trip fuel for Faro (along with the usual alternate fuel and final reserve fuel), we continue to Faro. If the fuel remaining comes to less than this figure, we divert to our alternate, Lisbon.
Fuel Policy and Fuel Monitoring 2
Figure 2.5 Oxford to Faro
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Figure 2.6 Oxford to Faro
Decision Point Procedure should not be attempted unless the departure fuel is sufficient to guarantee a reasonable expectation of there being enough fuel remaining at the Decision Point to permit continuation to the scheduled destination. The success of a Decision Point Procedure will depend on whether unforeseen events, such as not being cleared to the optimum cruise level or avoidance of weather, have caused the contingency fuel allowance to be used. The normal non-consumption of contingency fuel, which can be a considerable amount (usually 3% at least of the fuel between departure and Decision Point), permits Decision Point Procedure to be feasible and safe.
Departure |
Decision |
Destination |
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Point |
Airport |
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Destination |
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Alternate |
Alternate |
Figure 2.7 Decision point procedure
Comparing the Decision Point Procedure fuel requirement with the normal fuel requirements, the maximum fuel reduction available is the contingency fuel (3% or 5% of trip fuel) between Departure and Decision Point.
Alternatively, we can say that contingency fuel can be reduced down to that required between Decision Point and Destination.
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Special Cases 2 – Isolated Aerodrome Procedure
An ‘Isolated’ aerodrome is defined as an aerodrome for which there is no Destination Alternate. An island in an ocean is a good example, for instance, Easter Island in the South Pacific. In this case the aircraft might have to hold for longer than usual (e.g. in the case of a blocked runway or a tropical storm passing through) with no option of diverting. Reserves normally consist of contingency fuel, alternate fuel and final reserve fuel. In the case of an Isolated aerodrome there is no alternate, so there is no alternate fuel. Instead, for a jet or turboprop aircraft, the combination of final reserve fuel and additional fuel must comprise enough fuel to fly for two hours at normal cruise consumption after arriving at the destination aerodrome. CS-OPS 1 specifies that the fuel must include:
•Taxi fuel
•Trip fuel
•Contingency fuel
•Additional fuel if required but not less than:
•For aeroplanes with reciprocating engines, fuel to fly for 45 minutes plus 15% of the flight time planned to be spent at cruising level, or two hours, whichever is less.
•For aeroplanes with turbine engines, fuel to fly for two hours at normal cruise consumption after arriving overhead the destination aerodrome, including the final reserve fuel.
Fuel Policy and Fuel Monitoring 2
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