Have you ever realised how pilots know how much fuel they need for an aircraft? It is not as simple as it sounds. A lot of people think that it is the same as with the car, you put fuel nozzle into a car and just load the full tank with fuel, but, actually, the situation is different with the aircraft.
We will analyse the way pilots estimate how much fuel they need for their flight. Imagine that the plane has to fly from Warsaw to Vilnius, while choosing the airport in Riga as an alternate airport.
Let’s analyse the situation by types of fuel the aircraft needs to successfully complete the flight:
First of all, trip fuel is needed to take-off, climb, cruise, descend, approach and land. In brief, it is the fuel needed to fly from point A to B.
Secondly, contingency fuel is needed in case the weather or wind changes and the aeroplane has to navigate around or the air controller does not give the permission to fly into the requested flight level and has to stay in the lower level which leads to consuming more fuel.
Contingency fuel has to make up either 5% of the trip fuel or a minimum of 5 extra minutes which is mandatory by law.
Now imagine that while approaching the airport we are rejected from landing on the runway as another plane is blocking the way due to technical issues. That means the aeroplane will have to go around without being able to land at our destination and that is the moment when we need alternate fuel to land at an alternate airport which we have chosen during our briefing.
While approaching Riga airport, we get information that we cannot land either as runway inspection cars have just broken down. As we have used up all the trip fuel, contingency fuel and alternate fuel, we are left with final reserve fuel the amount of which is regulated by law and must make up a minimum of 30 minutes’ flying time and 1500 feet over the airport holding speed.
The time of those 30 minutes is needed to clear the runway and we will be the first for approach as we have declared fuel emergency as soon as we started using the final reserve fuel.
Pilots also have an option of adding extra fuel for situations when aircraft would be holding or doing long transitions as the flight might be affected by either the pilots’ unfamiliarity of a particular airport or its rush hours.
Last but not least, we need taxi fuel which gets us from the gate position to the runway, fuels the auxiliary power unit for air conditioning and starting the engine. Also, we can add even more taxi fuel, especially during winter, when the plane needs de-icing which extends our consumption of taxi fuel.