Fuel planning is an essential activity for air transportation and the general aviation industry since fuel consumption is at the top of the list when it comes to the costs of flying. From the business point of view, optimizing the amount of fuel used in each flight is vital so that such costs are kept as low as possible to increase profitability.
However, even for the recreational pilot fuel planning is relevant. With the high costs involved, it is not as simple as filling the tank and taking off, there are other aspects to consider.
We invite you to keep reading as we share the most critical aspects of fuel planning and the terms you should be familiar with when planning for your next flight.
What is fuel planning?
Fuel planning can be described as the activity of calculating the total amount of fuel required to complete a flight safely. This usually includes:
Final reserve fuel
From the list above, trip fuel and contingency fuel may be the easiest to understand. The first one refers to the amount of fuel needed to actually get from departure to destination, including takeoff, climb, cruise flight, descent, approach, and until touchdown at the destination. The second refers to the amount of fuel to account for bad weather, ATM-related extra movements, or flight level variations.
Recommended minimum contingency fuel
The minimum contingency fuel required is established by the International Civil Aviation Organization (ICAO) as the greater out of 5% of the trip fuel or 5 minutes holding consumption at 1500′ above destination airfield elevation computed based on calculated arrival weight. However, other authorities have changed the requirement and either decreased or increased the amount of contingency fuel.
We will now see the details of the other components of fuel planning listed above.
Before any flight, pilots are required to file for an alternate airport. This is a legal IFR requirement intended to guarantee there is enough fuel to reach another airport in the event that landing at the initial destination becomes impossible.
Therefore, alternate fuel refers to the amount pilots would need from the missed approach point at the destination aerodrome until the landing at the alternate aerodrome.
When planning alternate fuel, the necessary amount to achieve the following must be considered:
Time of missed approach at the destination airport.
Climb to enroute altitude, cruise, and descent at an alternate aerodrome.
Approach at alternate.
Landing at the alternate aerodrome.
Extra 45 minutes at normal cruising speed.
Sometimes two alternates are required by the corresponding authority. In such a case, alternate fuel will be planned to guarantee the farthest alternate can be reached.
Although the alternate airport or airports are filed in advance, the pilot may divert the flight to any other depending on the specific situation. The priority is safety, not what was initially filed. Also, it is important to highlight that the planning must include enough fuel to land with reserves onboard according to regulations.
Planning the fuel needed for a flight must consider more than just the time in the air. Aircraft consume fuel at every stage of the flight, and this includes taxiing at the airport.
So, taxi fuel refers to the amount needed before takeoff and after landing. It will normally include fuel for pre-start APU consumption, engine start, and the actual taxiing. It is generally planned as a fixed quantity for an average taxi time.
However, apart from the average taxi time at the corresponding airport, other specific aspects like normal ground delays and any anticipated deicing delays should be considered to adjust the taxi fuel accordingly.
Ballast fuel and zero fuel weight
Firstly, it is important to remember that the stability of aircraft while in the air is critical for safety, so keeping the center of gravity within limits is essential. This is achieved with an amount of fuel considered ballast fuel. In general, this is the fuel that is not used for any stage of the flight, and it will be used only if emergency circumstances require it.
Then, there are some airplane types where a zero fuel weight above a defined threshold requires a minimum amount of fuel to be carried in the wings through all phases of flight to prevent excessive wing bending.
The truth is that there is no such thing as too much fuel when it comes to safety. As many pilots, especially flight instructors like to say, “nothing is more useless during a flight than the fuel left on the ground.”
Therefore, extra fuel refers to the amount added at the captain’s or dispatcher’s discretion. The pilot in command may ask for extra fuel beyond the minimum fuel required legally if deemed necessary given the possible scenarios and variables for the planned flight.
Final reserve fuel
As it was mentioned above, some authorities require enough fuel to hold for 45 minutes. However, final reserve fuel usually refers to the minimum fuel required to fly for 30 minutes 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.
How do you calculate the fuel needed to fly?
Finally, after determining the amounts for each of the fuel requirements described above, those amounts must be added up to calculate the total amount of fuel needed to fly. However, this takes more than a simple addition.
In general, the trip fuel component is calculated based on the relation of fuel consumption of the aircraft with the time it takes to get to the destination, plus legally required fuel reserves for diversions and delays. This is done by multiplying the estimated flight time by the rate of consumption of the aircraft.
To illustrate this, for an Airbus A380, the rate of consumption is 4,050 Gallons/hour. So, for a flight leg of 8 hours and a half, the fuel required would be 8.5 x 4,050 = 34,425 gallons of fuel required for the flight leg. Then the other components are added to this result, and they usually represent percentages of the calculated leg which are given by the regulations.
As you can see, it takes more than just filling the tank.
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A mechanical engineer and aviation enthusiast dedicated to share some knowledge by creating top-notch content, especially in engineering and aviation topics.
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