What is Defueling?
Some aircraft have such limitations that it is not always possible to load four people with baggage and full fuel for a long trip. This might happen when the airplane was topped up the night before and you arrive with three passengers for a trip the next morning. The only option could then be (apart from a different aircraft) to defuel the airplane. This can be done by:
pumping excess duel into drums by a hand pump, make sure the suction end is clean before inserting it into the aircraft tanks
or by opening the drain points and let the fuel run via a funnel with filter into a container suitable for aviation fuel
if you defuel and store AVgas keep in mind that the shelf life is about a year (commercial operators) due to gum forming caused by oxidation
Make sure to take every safety precaution when defueling the aircraft as the dangers remain the same as with refueling.
In simple understanding, 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. The pump on a fuel truck can also be used to draw fuel out.
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 in a separate container from good fuel, treated if possible, or disposed of properly.
Take measures to ensure that contaminated fuel is never placed onboard an aircraft or mixed with good fuel. Second, the manufacturer may have requirements for good 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.Good 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 from a tank requiring maintenance to another tank to avoid the defueling process.
