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Fuel must be removed from an aircraft’s fuel tank when maintenance must be done on the fuel system, when the fuel level gages are to be calibrated, and when work on the aircraft requires use of electrical equipment or other equipment that might generate heat or sparks. The tank must also be defueled if the aircraft is to be shipped or stored. Defueling is more dangerous than fueling because, even though relatively small amounts of fuel are involved, the procedure is more difficult and drainage provisions are usually inconvenient. All safety precautions must be observed. The general rule of defueling is that it must be done outdoors without damage to the aircraft or its fuel system, without fuel waste, and without safety violations. Aircraft fuel tanks must be defueled by power or by gravity. For speed and efficiency, power should be used to remove most of the fuel and only final draining should be done by gravity. These methods are described below.

Power Defueling

The bulk of the fuel in an aircraft’s tanks should be removed by suction. A pump/engine assembly or the pump of a refueler provides the power. The aircraft can be defueled either with a defueling tube or by using a piece of salvaged suction hose.

  • Defueling tube. A defueling tube is fitted onto the suction hose. The tube is inserted into the tank and most of the fuel is pumped out.
  • Suction hose. A piece of 1- or 1 1/2-inch salvaged suction hose may also be used to defuel an aircraft. The end that will be inserted into the tank is cut at an angle so that the reinforcing wire is cut only once. The cut end of the reinforcing wire is also rounded to keep it from damaging the fuel tank. The hose is inserted into the tank and most of the fuel is pumped out.

Gravity Defueling

Gravity defueling is the process of draining the tanks by opening the drain valves or petcocks of the aircraft fuel system. It is a slow and dangerous process. Some suitable container must be placed under the valves to catch the fuel. Except in an emergency, this method should be used only to complete the draining of the aircraft fuel system after the bulk of the fuel has been removed by a pump.


Aircraft refueling must be done outdoors, except when the responsible commander directs indoor defueling. When defueling is done outdoors, general safety precautions must be followed. Defueling may be into a tank vehicle or into a container.

General Safety Precautions

The general safety precautions for outdoor defueling are as follows:

  • Aircraft fuel tank openings must be at least 50 feet from any hangar or building. They must be the proper minimum distance from radar equipment.
  • No aircraft, vehicle, electrical equipment, open-flame device, or any other spark generator must be allowed to operate within 50 feet of the aircraft.
  • No smoking is allowed within 50 feet of the aircraft.
  • Aircraft engines and radios must be shut down.
  • Only those personnel actually required to conduct the defueling operation and to operate the fire equipment are allowed within 50 feet of the aircraft.
  • All defueling operations must be stopped if there is an electrical storm in the immediate area or if there is a fire, fuel spill, crash, or accident at the refueling point or airfield.
  • The fire chief or senior fire officer will decide when a defueling operation warrants a fire truck and personnel present. Fuel service personnel will man fire extinguishers for all defueling operations.

Tank Vehicle Defueling

The procedures for defueling into a tank vehicle are as follows:

  • Drive the tank vehicle into the same position as when refueling, but park it as far from the aircraft as the length of the hose will permit. Park the tank vehicle so that there is a clear and open route to drive away from the aircraft in an emergency.
  • Ground the tank vehicle by connecting one clip of the ground cable’s Y-cable to a ground rod. If there is no ground rod in place at the site, drive the vehicle’s ground rod to the specified depth. See Chapter 2 for more information.
  • Ground the aircraft by connecting the clip at the other end of the Y-cable to an unpainted surface of the aircraft other than the radio antenna or propeller.
  • Bond the defueling tube to the aircraft with a bonding plug or clip. A length of suction hose may be used if a defueling tube is not available.
  • Remove the plug from the aircraft fuel port, if appropriate, or slide the shield off the open port adapter opening of the CCR receiver.
  • Insert the defueling tube or length of suction hose into the tank. If the aircraft has a drain port, attach the suction hose to the aircraft’s drain port using the required adapters.
  • Start the pump and pump the fuel out. As soon as the flow stops, shut down the pump.
  • Remove the defueling tube or length of suction hose from the tank, and close the tank.
  • Remove the bond and reel up the hose.
  • Remove the ground connection to the aircraft, then the ground connection between the tank vehicle and the ground rod. Reel up the grounding cable.
  • Drive the tank vehicle away.

Container Defueling

Gravity defueling is the procedure to place fuel into a container. It is a dangerous procedure. The fuel builds considerable static charge as it falls into the container. It also splashes and agitates the fuel already in the container. The soldier who opens the fuel system’s drain valves or petcocks is likely to get his arm and sleeve wet with fuel. Fuel soaked clothing should be removed with care. Observe all safety precautions. Fuel should be washed off the skin with soap and water. A fire truck (as required) or personnel with fire extinguishers must stand by during the entire operation. The procedures for defueling into containers are as follows:

  • Ground the container by attaching the grounding wire clip to the container on one end and a ground rod at the other end.
  • Ground the aircraft to the ground rod by connecting a cable to an unpainted surface of the aircraft, other than the radio antenna or propeller, and to a ground rod driven to the specified depth.
  • Open the valves or petcocks, and drain the remaining fuel from the aircraft fuel system.
  • Remove the ground to the aircraft after draining is complete, and then remove the ground to the container of the fuel.


When an aircraft is scheduled for maintenance, the fuel system may have to be drained. Whenever possible, the aircraft should be defueled outdoors before it is moved into a hangar or maintenance tent. However, during routine maintenance disassembly, an unexpected condition can be discovered that makes defueling necessary. If the aircraft is either in a jig or on jacks when the discovery is made, moving the aircraft outdoors is probably impossible. In such a situation, the responsible commander must be notified immediately and all alternatives to indoor defueling should be considered. If indoor defueling is to occur, follow the procedures described below.

Preparing to Defuel

A number of procedures must be followed when preparing to defuel indoors. These are as follows:

  • Move all aircraft that can be moved out of the hangar and park them at least 50 feet away from the hangar.
  • Open the main doors of the hangar, and close any office or shop doors that open into a hangar. Opening the main doors provides maximum ventilation and will allow the force of an explosion to dissipate.
  • Turn off all engines, electrical equipment, or other possible spark sources within 50 feet. Do not start or continue the operation if there is an electrical storm in the immediate area or a fuel spill, crash, fire, or any other emergency at the airfield.
  • Clear at least 50 feet of all personnel and equipment that are not required for defueling.


In a hangar, a water pipe or a buried grid usually provides the ground connection to an aircraft. In a tent, a ground rod provides this ground connection.


Procedures to defuel an aircraft indoors are the same as those for defueling into a tank vehicle or container outdoors.


Drained fuel should be disposed of properly. Dispose of all drained fuel according to AR 710-2. See Chapter 13 for more information.

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