Proper fueling and defueling procedures are essential for safe aircraft operation and fuel system integrity. Incorrect fueling practices can result in contamination, structural damage, fire hazards, or improper fuel loading. Maintenance personnel involved in aircraft fueling operations must follow approved procedures, observe all safety precautions, and ensure that the correct fuel is handled properly at all times.
Fueling
Always fuel aircraft outside, not in a hangar where fuel vapors may accumulate and increase the risk and severity of an accident. Generally, there are two types of fueling procedures: over-the-wing refueling and pressure refueling.
Over-the-wing refueling is accomplished by opening the fuel tank cap on the upper surface of the wing or fuselage, if equipped with fuselage tanks. The fueling nozzle is carefully inserted into the fill opening and fuel is pumped into the tank. This procedure is similar to refueling an automobile gas tank. When finished, the cap is secured, and subsequent tanks are opened and refilled until the aircraft has the desired fuel load onboard.
Pressure refueling is accomplished through a fueling receptacle located at the bottom, front, or rear of the aircraft. A pressure refueling nozzle locks onto the fueling port at the aircraft fueling station. Fuel is pumped into the aircraft through this secured and sealed connection. Gauges are monitored to ascertain when the tanks are properly loaded. An automatic shutoff system may be incorporated into the aircraft fueling system. It closes the fueling valve when the tanks are full. [Figure 1]
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| Figure 1. A float switch installed in a fuel tank can close the refueling valve when the tanks are full during pressure fueling of an aircraft. Other more sophisticated automatic shutoff systems exist |
Precautions should be used with either type of fueling. First and foremost, it is absolutely essential that the correct fuel be put in the aircraft. The required fuel type is placarded near the fill port on over-the-wing systems and at the fueling station on pressure refueled aircraft.
If there is any question about which fuel to use, the pilot in command, other knowledgeable personnel, or the manufacturer’s maintenance/operations manual should be consulted before proceeding. An over-the-wing refueling nozzle for turbine engine fuel should be too large to fit into the fill opening on an aircraft utilizing gasoline.
Clean the area adjacent to the fill port when refueling over the wing. Ensure the fuel nozzle is also clean. Aviation fuel nozzles are equipped with static bonding wires that must be attached to the aircraft before the fuel cap is opened. [Figure 2]
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| Figure 2. An AVGAS fueling nozzle with static bonding grounding wire |
Open the cap only when ready to dispense the fuel. Insert the nozzle into the opening with care. The aircraft structure is much more delicate than the fuel nozzle, which could easily damage the aircraft. Do not insert the neck of the nozzle deeply enough to hit bottom. This could dent the tank, or the aircraft skin, if it is an integral tank. Exercise caution to avoid damage to the surface of the airframe by the heavy fuel hose. Lay the hose over your shoulder or use a refueling mat to protect the paint. [Figure 3]
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| Figure 3. Over-the-wing refueling a Cessna |
When pressure refueling, the aircraft receptacle is part of a fueling valve assembly. When the fueling nozzle is properly connected and locked, a plunger unlocks the aircraft valve so fuel can be pumped through it. Normally, all tanks can be fueled from a single point. Valves in the aircraft fuel system are controlled at the fueling station to direct the fuel into the proper tank. [Figure 4]
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| Figure 4. This panel at the pressure refueling station has valve position switches and quantity gauges to be used during refueling. Valve open position lights are adjacent to the switches for each tank |
Ensure that the pressure developed by the refueling pump is correct for the aircraft before pumping fuel. Although similar, pressure fueling panels and their operation are different on different aircraft. Refueling personnel should be guided through the correct use of each panel. Do not guess how the panel and associated valves operate.
When fueling from a fuel truck, precautions should be taken. If the truck is not in continuous service, all sumps should be drained before moving the truck, and the fuel should be visually inspected to be sure it is clean and bright. Turbine fuel should be allowed to settle for a few hours if the fuel truck tank has recently been filled or the truck has been jostled, such as when driven over a bumpy service road at the airport. Properly maneuver the fuel truck into position for refueling.
The fuel truck should approach the aircraft slowly. The truck should be parked parallel to the wings and in front of the fuselage if possible. Avoid backing toward the aircraft. Set the parking brake and chock the wheels. Connect a static bonding cable from the truck to the aircraft. This cable is typically stored on a reel mounted on the truck.
There are several additional good practices that should be employed when refueling an aircraft. A ladder should be used if the refuel point is not accessible while standing on the ground. Climbing onto the aircraft to access fueling ports is possible, but it does not provide the stability of a ladder and may not be appreciated by the aircraft owner. If it is necessary to walk on the wings of the aircraft, do so only in designated areas, which are safe.
Filler nozzles should be treated as the important tools that they are. They should not be dropped or dragged across the apron. Most have attached dust caps that should be removed only for the actual fueling process and then immediately replaced.
Nozzles should be clean to avoid contamination of the fuel. They should not leak and should be repaired at the earliest sign of leak or malfunction. Keep the fueling nozzle in constant contact with the filler neck spout when fueling. Never leave the nozzle in the fill spout unattended. When fueling is complete, always double-check the security of all fuel caps and ensure that bonding wires have been removed and stowed.
Defueling
Removing the fuel contained in aircraft fuel tanks is sometimes required. This can occur for maintenance, inspection, or due to contamination. Occasionally, a change in flight plan may require defueling. Safety procedures for defueling are the same as those for fueling. Always defuel outside.
Fire extinguishers should be on hand. Bonding cables should be attached to guard against static electricity buildup. Defueling should be performed by experienced personnel, and inexperienced personnel must be checked out before doing so without assistance.
Remember that there may be a sequence in defueling an aircraft’s fuel tanks just as there is when fueling to avoid structural damage. Consult the manufacturer’s maintenance/ operations manual(s) if in doubt.
Pressure fueled aircraft normally defuel through the pressure fueling port. The aircraft’s in-tank boost pumps can be used to pump the fuel out. A fuel truck pump can also be used to extract fuel. These tanks can also be drained through the tank sump drains, but the large size of the tanks usually makes this impractical. Aircraft fueled over the wing are normally drained through the tank sump drains. Follow the manufacturer’s procedure for defueling the aircraft.
What to do with the fuel coming out of a tank depends on a few factors. First, if the tank is being drained due to fuel contamination or suspected contamination, it should not be mixed with any other fuel. It should be stored separately from uncontaminated fuel, treated if possible, or disposed of properly. Take measures to ensure that contaminated fuel is never placed onboard an aircraft or mixed with serviceable fuel.
Second, the manufacturer may have requirements for serviceable fuel that has been defueled from an aircraft, specifying whether it can be reused and the type of storage container in which it must be stored. Above all, fuel removed from an aircraft must not be mixed with any other type of fuel.
Serviceable fuel removed from an aircraft must be handled with all precautions used when handling any fuel. It must only be put into clean tanks and efforts must be made to keep it clean. It may be put back in the aircraft or another aircraft if the manufacturer allows. Large aircraft can often transfer fuel internally from one tank to another to avoid the defueling process.
Fire Hazards When Fueling or Defueling
Due to the combustible nature of AVGAS and turbine engine fuel, the potential for fire while fueling and defueling aircraft must be addressed. Always fuel and defuel outside, not in a hangar where vapors can accumulate to a combustible level. Clothing worn by refueling personnel should not promote static electricity buildup. Synthetics, such as nylon, should be avoided. Cotton has proved to be safe for fuel handling attire.
The most controllable of the three ingredients required for fire is the source of ignition. It is absolutely necessary to prevent a source of ignition anywhere near the aircraft during fueling or defueling. Any open flame, such as a lit cigarette, must be extinguished. Operation of nonessential electrical or electronic equipment should be avoided in the fueling area.
It is important to note that fuel vapors proliferate well beyond the actual fuel tank opening and a simple spark, even one caused by static electricity, could be enough for ignition. All potential ignition sources must be eliminated.
Spilled fuel poses an additional fire hazard. A thin layer of fuel vaporizes quickly. Small spills should be wiped up immediately. Larger spills should be handled in accordance with approved airport or operator spill-response procedures. Do not sweep fuel that has spilled onto the ramp.
Class B fire extinguishers need to be charged and accessible nearby during the fueling and defueling processes. Fueling personnel must know their locations and proper operating procedures. In case of an emergency, the fuel truck, if used, may need to be quickly driven away from the area. For this reason, it should be positioned correctly on the ramp relative to the aircraft.