For anyone that has never seen how the process of refueling an aircraft takes place, reading the words in the title might create a picture of an aircraft in a gas station being refueled like a car or other vehicles.
However, there are significant differences. First, the type of fuel used is different, and then the way it is done will depend on whether the aircraft is on the ground or flying. Yes, aircraft can be refueled in the air, but this is mainly used in military aviation.
We invite you to keep reading to learn all you need to know about refueling an aircraft and the risks associated with it as well as the safety measures required to mitigate the risk.
What is aircraft refueling?
Refueling an aircraft can be described as the process of adding fuel to the tank of the aircraft or at least providing enough fuel for the aircraft to complete the flight.
A common practice in aviation is to plan a long flight with an adequate stopover to have the aircraft fueled without passengers leaving their seats. Of course, appropriate equipment and measures must be used to guarantee these operations are performed safely, as we will describe below.
What are the types of fuel used in aircraft?
Generally speaking, there are two main types of fuel. The fuel used by aircraft with turbine engines and the fuel used by aircraft with piston engines.
The fuel is known as kerosene fuel for turbine engines, but it is also called jet fuel. One of the most relevant properties of this fuel is its higher ignition point.
In the case of piston engines, the so-called aviation gasoline is used. However, the truth is that this type of fuel is mainly diesel fuel.
What are the two types of methods of refueling?
As we mentioned above, the two major categories to classify refueling methods can be refueling on the ground and in-air refueling. While in-air refueling is mostly reserved for military aviation, we want to describe the fascinating process. Yet, we will describe ground refueling since it is the most common in passenger aircraft.
Generally, fuel is stored in facilities that are around or near the airport. From these facilities, the fuel is transported through a piping system, usually called a transfer fuel line, to the points at the airport where the fuel is needed. This could be one of two options:
Underground hydrants are usually located in a specific area where refueling takes place.
Loading stations where trucks called refuelers have their tanks loaded to take the fuel to the airplanes.
This first step of the process of moving the fuel from the storage to the area where it is needed usually depends on the airport. It is also important to highlight that the procedures that will be described below may vary among airlines. However, third parties and their personnel generally offer these services, and they commonly follow the same procedures.
The process usually takes place this way:
Upon the airplane’s arrival, a refueler is sent to its position. This could be a tank refueler or what is known as a hydrant car or towable unit, depending on the airport. In any case, small tank trucks are usually available as a backup.
Positioning the refueler
The refueler is positioned under the wing or close to it in the case of small jets. Most airplanes have the fueling connection in one of their wings, although some small ones have it on top of it.
After the refueler is positioned and before the hoses are rolled out to connect them, the system is grounded with a special cable in a process known as electrical bonding.
This is an essential step for safety since it creates protection against a possible electrostatic discharge that the fuel flow might generate. This type of discharge could ignite fuel vapors, resulting in fire and possible explosion, even with the tiniest spark.
According to Airbus’s guide on safe refueling, electrical bonding also prevents “any spark from appearing when the ground operator connects the refueling hose to the aircraft coupling.”
Connecting the fuel hoses
This is the final step before the airplane tank can start receiving the fuel. A trained technician carefully places and secures the hose to the fueling point to connect the fuel hose. These are called single-point fueling systems, and they allow to fill with fuel all the tanks on both wings and in the fuselage if that is the case. The main intention is to reduce the possibility of contamination and the possibility of a spark igniting the fuel and its vapors while connecting different hoses.
It is essential to highlight that lifting equipment may be necessary for the technician to reach the connection point when fueling the tank of a big airplane.
Filling the tanks with the right amount of fuel
The final step of the whole process is ensuring the tank gets an adequate amount of fuel. This requires accurate calculation based on different aspects such as the airplane’s weight, number of passengers, and range. It also requires good communication between the airline and the cabin crew so they can pass on the information to the operators to optimize both the flight and the refueling schedules.
How does in-flight refueling work?
Many things are fascinating in aviation, and this is definitely one of them. While it has been done for a long time already, the also called aerial refueling could be considered both a science and an art.
It requires a big airplane (the tanker) to fly in formation with a smaller one, usually the jet that needs refueling. The pilots need to be very accurate to make sure the system’s connection, generally consisting of a hose with a drogue and a retractable probe in the receiver, is a success.
We won’t go into further detail here, but you get the picture of how difficult and dangerous this could be and why it is not used with passengers.
What are the risks associated with aircraft refueling?
There is always some risk when working with a flammable substance. Still, the operators need to consider other aspects to avoid accidents like dropping tools or any device from the heights or inside the hydrant pit.
Also, we already mentioned how an electrostatic discharge can be generated and how it should be avoided. In addition, personal electronic devices (PEDs) are not permitted near the area where refueling takes place because they can quickly generate or induce a spark or interfere with the operation of gauges and carry the risk of using the wrong pressure, among other things.
Finally, even with the right measures in place, it is always necessary to have an emergency shutdown system and evacuation plan for the crew and the passengers in case of imminent risk.
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Jet pilot @NASA
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