What is reserve fuel in Aviation

Flight crews shall ensure that the pre-flight calculation of fuel required for a given flight includes:

Taxi Fuel

Taxi fuel is the fuel used prior to take-off and must include pre-start APU consumption, engine start and taxi fuel. It shall not be less than the amount expected to be used prior to take-off. Taxi fuel is usually a fixed quantity for average taxi duration. Local operating conditions at the departure aerodrome shall be taken into consideration and the taxi fuel adjusted accordingly. These conditions shall include at least average taxi time, any known ground delays, expected runway combinations, NOTAM’s, meteorological conditions, air traffic services procedures (e.g. LVP, CDM) delays and any anticipated de-icing delays.

Trip Fuel / Fuel to Destination

The Trip fuel is the required fuel quantity from brake release on take-off at the departure aerodrome to the landing touchdown at the destination aerodrome. This quantity includes the fuel required for: take-off, climb to cruise level, flight in level cruise including any planned step climb or step descent, flight from the beginning of descent to the beginning of approach, approach, landing at the destination.

Trip fuel must be adjusted to account for any additional fuel that would be required for known ATS restrictions that would result in delayed climb to or early descent from planned cruising altitude.

Contingency Fuel

Contingency fuel is carried to account for additional enroute fuel consumption caused by unforeseen factors such as wind, routing changes or ATM restrictions. In general terms, the minimum contingency fuel is the greater of 5% of the trip fuel or 5 minutes holding consumption at 1500' above destination airfield elevation computed based on calculated arrival weight. However, some regulators, with special approval, allow reduction to 3% of trip fuel with use of enroute alternates or to specific time increments depending upon demonstrated performance criteria capabilities from the Operator. The Commander may consider refueling should any delay result in the consumption of contingency fuel before take-off. Contingency fuel shall not be planned as a substitute for taxi fuel as defined above.

Contingency fuel required as a result of ETOPS restrictions must not be confused with contingency fuel described in this context.

Alternate Fuel

Alternate fuel is the amount of fuel required from the missed approach point at the destination aerodrome until landing at the alternate aerodrome. It takes into account the required fuel for: missed approach at the destination airport, the longest route from the furthest Missed Approach Point, the cruise and descent at alternate aerodrome according to an expected airway/route, transition (to prevent the possible bottleneck situation in case of airport closure), approach at alternate, and landing at the alternate aerodrome.

When two alternates are required by the Authority, alternate fuel must be sufficient to proceed to the alternate which requires the greater amount of fuel.

Normally a flight shall be planned with an alternate aerodrome. Planning with no alternate shall be restricted to exceptional circumstances.

Provided all three following conditions are fulfilled, it is allowed to plan without destination alternate:

1. It is only allowed to plan without destination alternate, if the flight cannot be planned with all traffic load and alternate fuel. In this rare case, no alternate flight planning can be executed subject to the Commander’s decision; and
2. The duration of the planned flight from take-off to landing or, in the event of in-flight replanning, the remaining flying time to destination does not exceed 2 hours; and
3. Two separate runways are usable at the destination aerodrome, and the appropriate weather reports and/or forecasts for the destination aerodrome indicate that for the period from 1 hour before until 1 hour after the expected time of arrival at the destination aerodrome, the ceiling will be at least 2 000 ft (600 m) or the circling height +500 ft (150 m), whichever is greater, the ground visibility will be at least 5 km, and no thunderstorms or shower activities are present or expected in the vicinity of the aerodrome

Alternate Aerodromes must be adequate, which means they have the necessary RFF and ATC services and facilities available, meet aircraft performance requirements and are operational at the expected time of use.

Final Reserve Fuel / Fixed Reserve Fuel / Holding Fuel

Final reserve fuel is the minimum fuel required to fly for 45 minutes[1] at 1,500 feet above the alternate aerodrome or, if an alternate is not required, at the destination aerodrome at holding speed in ISA conditions. If the flight is planned without alternate, the final reserve fuel should be no less than 60 minutes holding fuel.

Reserve Fuel / Minimum Diversion Fuel

Reserve fuel or Minimum Diversion fuel is the sum of Alternate fuel plus Final Reserve fuel. Minimum diversion fuel does not imply that a diversion must be initiated. Depending on operational circumstances committing to the destination is also an option.

Additional Fuel

Additional fuel is fuel which is added to comply with a specific regulatory or company requirement. Examples include fuel for technical deficiencies such as engine failure or loss of pressurization, ETOPS fuel, fuel required for a remote or island destination where no alternate is available.

Extra Fuel

Extra fuel is fuel added at the discretion of the Commander. The Commander must consider the viability of the planned route and alternates, and consider whether any statistical contingency is valid to the particular conditions on the day.

Block Fuel / Total Fuel on Board

Block fuel is the total fuel required for the flight and is the sum of the Taxi fuel, Trip fuel, Contingency fuel, Alternate fuel, Final Reserve fuel, Additional fuel and Extra fuel.

[1] Technical University of Munich study: “Risk Analysis of the EASA Minimum Fuel Requirements. Considering the ACARE-defined Safety Target” (2016); currently awaiting publication in a scientific journal. This study specifically supports 45 minutes for Final Reserve Fuel.

Introduction

An aeroplane shall carry a sufficient amount of usable fuel to complete the planned flight safely and to allow for deviation from the planned operation.

In this document we will present only the ICAO requirements. Other areas of the world like FAA, Europe can have additional requirements and restrictions.

The amount of usable fuel carried shall, as a minimum, be based on:

• Aeroplane specific data from a fuel consumption monitoring system or aeroplane manufacturer data
• Operating conditions for the planned flight (mass, weather reports, air traffic services procedures and restrictions, NOTAM …)

The pre-flight calculation of usable fuel required shall include:

• Taxi fuel
• Trip fuel
• Contingency fuel
• Destination alternate fuel
• Final reserve fuel
• Additional fuel
• Discretionary fuel

It is the amount of fuel expected to be consumed before take-off during start-up and taxi operation.

It is the amount of fuel required to enable the aeroplane to fly from take-off, or the point of in-flight re-planning, until landing at the destination aerodrome taking the operating conditions into account.

It is the amount of fuel required to compensate for unforeseen factors.

It shall be 5% of the planned trip fuel based on the consumption rate used to plan the trip fuel and it shall not be lower than the amount required to fly for 5 minutes at holding speed at 450m (or 1500ft) above the destination aerodrome in standard condition.

Unforeseen factors could have an influence on the fuel consumption or could be in deviation of the expected fuel consumption like deviations from forecast meteorological conditions, extended taxi time, extra holding procedures, deviation from planned routing or different cruising levels.

It is the amount of fuel required, where a destination alternate aerodrome is required or planned:

• To perform a missed approach at the destination aerodrome
• To climb to the expected cruising altitude between destination aerodrome and alternate aerodrome
• To fly the expected route between destination aerodrome and alternate aerodrome
• To descend to the point where the expected approach is initiated
• To conduct the approach and landing at destination alternate aerodrome

Where two destination alternate aerodromes are required, the amount of fuel calculated shall take into account the aerodrome which requires the greater amount of alternate fuel.

Where a flight is operated without a destination alternate aerodrome, the amount of fuel required to enable the aeroplane to fly for 15 minutes at holding speed at 1500ft or 450m above destination aerodrome elevation in standard conditions.

Where the destination aerodrome is an isolated aerodrome: (rare cases)

• For a reciprocating engine aeroplane, the amount of fuel required to fly for 45 minutes plus 15% of the flight time planned to be spent at cruising level including the final reserve fuel or 2 hours, whichever is less
• For a turbine-engined aeroplane, the amount of fuel required to fly 2 hours at normal cruise consumption above the destination aerodrome, including the final reserve fuel.

Final reserve fuel

It is the amount of fuel calculated using the estimated mass on arrival at the destination alternate aerodrome, or destination aerodrome when no destination alternate aerodrome is required :

• For a reciprocating engine aeroplane, the amount of fuel required to fly for 45 minutes under speed and altitude specified by the operator of the aircraft
• For a turbine-engined aeroplane, the amount of fuel required to fly 30 minutes at holding speed at 1500ft or 450m above aerodrome elevation in standard conditions.

It is the amount of fuel required if the minimum fuel calculated in Trip + Contingency + Destination alternate + Final reserve fuel is not sufficient to:

• Allow the aeroplane to descend as necessary and proceed to an alternate aerodrome in the event of engine failure or loss of pressurization on the assumption that such a failure occurs at the most critical point along the route
• Fly 15 minutes at holding speed at 1500ft or 450m above destination aerodrome elevation in standard conditions
• Allow EDTO (extended diversion time operations) critical fuel scenario
• Allow other restrictions not covered by previous requirements

It is the extra amount of fuel to be carried at the discretion of the pilot-in-command.

This fuel can be extra fuel you may carry to perform a pilot exam in order to cover all planned exercises, or it can be the extra fuel, you may carry to perform a flight during an ATC exam covering extra holding patterns due to traffic flow.

Management

The fuel should be monitored through all the phases of the flight; it is really important for the pilot in command to ensure the best methods and techniques in order to guarantee a proper operation and the safety of the flight.

The pilot in command shall ensure that there is enough fuel to complete the flight including:

• Ground services vs APU start (Increased fuel burn).
• Departure delays that could result in more use of fuel through the taxi operation. (Weather, delays, NOTAMS should be read in order to get the latest information of the aerodrome)
• De-icing (If De-icing will be performed at a remote position, the taxi fuel should be increased in order to achieve the taxi time fuel for departure)
• Route from the destination airfield to the worst alternate

Weight and balance should be checked in order to ensure the proper distribution of the payload and fuel.

The pilot in command shall take into account these parameters:

• Push-back time should be taken into account, at the same time, the engine start should be delayed until close to or reaching the tug disconnection position to conserve fuel.

In the event of some delays, weather situations, emergencies, traffic flow, the pilot in command should be aware of his minimum brake release fuel, some actions like shut down one engine; change the predicted fuel profile will ensure a better fuel conservation.

When possible, the pilot in command should consider:

• A de-rated take-off.
• The SID route (Opposite direction departures)

Check your V-Speeds and Flaps configuration in order to achieve the planned performance/fuel consumption over the runway.

The PIC should know that the take-off manoeuvre demands a high fuel flow operation from the aircraft. Optimized thrust vs optimized flaps will ensure a conservative fuel flow.

The pilot in command should use:

• Cost index and planned climb speed (must be used all the time).
• High speed climb and altitude level offs increase the fuel consumption, if it is necessary reduce the airspeed, this way the fuel penalty will be decreased.

Cruise

The pilot in command shall adjust the cruise profile when necessary to achieve the best profile:

• Compare cruise profile versus the wind, temperature and weight.
• Over the top of descent, check your fuel reserves in order to be satisfied with the minimum legal fuel required for the approach.

If the optimum cruise altitude could not be reached adjust the cost index/speed to reach a best profile.

The pilot in command shall consider:

• Reduced airspeed through descent guarantees low fuel consumption
• A descent before the top of descent in order to achieve the low speed descent.

The optimum descent profile is the one that it is performed at idle speed.

Once the holding clearance has been received, the pilot should start a speed decrease in order to reduce the fuel consumption at the hold.

It is important to be familiarized with the fuel reserves; this way the pilot could decide if he would be able to hold until the expected further clearance time (EFC). If there is insufficient fuel, the holding clearance must be refused or negotiated to get a better EFC.

A diversion should be initiated if the fuel reaches the diversion requirements.

The pilot in command should try to maintain a clean configuration as long as practical. The pilot in command should consider:

• Reduced final flap setting for the approach (Less drag)
• Reduced landing flap setting which increases the fuel conservation.
• Idle reverse instead of full reverse thrust which results in fuel savings.

It is important to know that a low use of the reverse could result in a higher brake use.

On the ground, the pilot in command shall reduce the APU start time, if possible request the ground services; this will reduce the fuel penalty created by the APU usage.

Pilots should be aware of their fuel regulations and policies in order to achieve the highest standards of safety and awareness.

In-Flight Management and Decision Making

The pilot in command must verify that fuel checks are performed in-flight at several intervals.

The fuel at the destination aerodrome should not be less than the required alternate fuel plus the final reserve fuel, if no alternate aerodrome is required it should not be less than the final reserve fuel.

If during a fuel check the expected fuel at the destination aerodrome will be less than the alternate fuel plus the final reserve fuel, the pic should take the decision to continue taking into account the future factors (delays, ATC instructions …) or divert to the nearest aerodrome.

On the other side, if alternate aerodrome is not required, the pic should be aware that he should not land below the final reserve fuel.

Diversion factors could be:

• Route alteration due to meteorological effects
• Depiction to a lower flight level
• Different route by ATC
• Engine complete or partial failure

Table shows a route plan with the time and trip fuel expectation in lbs

• Standard aircraft weights, Fuel management for general aviation

• ICAO documentation Annex 6 - Operation of Aircraft - Part I - International Commercial Air Transport - Aeroplanes - 10th Edition July 2016 - Chapter 4.3.6

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