FUEL SYSTEM SERVICING

General: Aircraft fuelling is an extremely important operation for a service facility, but it is often assigned to a person just getting started into the aviation service business. It is important from a business standpoint because the line service per­sonnel are the direct contact between the facility and the customer. And, economically, line servic­ing is important because it takes only one impro­perly fuelled aircraft to generate enough lawsuits to wipe out most businesses.

Checking Fuel for Contaminants: When servicing an aircraft fuel system, you must be extremely sure that you are furnishing the correct grade of fuel for the aircraft and that the fuel is free from contamination. Some of the business aircraft flight crews will demand a check -of the fuel before it is pumped into their aircraft. This is a good policy as it assures that the fuel is free from water and other types of contamination that could cause engine failure

. Types of contaminants:

a.   Solid particles: Sand blown into the storage tanks or into the aircraft tank during the fuelling operation or rust from unclean storage tanks are solid particles which can clog strainers and restrict the flow of fuel.

b.                                    Surficant:                These are partially soluble compounds which are by-products of the fuel processing, or they may come from fuel additives. They have the tendency to adhere to other contaminants and cause them to drop out of the fuel and settle to the bottom of the fuel tank as sludge.

c. Water:            Although it has always been present in avia­tion fuel, water is now considered to be a major source of contamination since aircraft fly at alti­tudes; where the temperature is low enough to cause water entrained, or “dissolved,” in the fuel to precipitate out and form free water. This free, water can freeze and clog the fuel screens.

d.                                    Micro organisms: Tiny micro organisms grow from airborne bacteria and gather in the fuel. They lie dormant until they can come into contact with free water, but then they grow at a prodigious rate as they live in the water and feed on the hydrocarbon fuel, and on some of the surficant contaminants. The scum which they form holds water against the walls of the fuel tanks and causes corrosion.

2. Detection of contaminants:

Draining a sample of fuel from the main strainers of an aircraft has in the past been con­sidered an acceptable method of assuring that the fuel in the system is clean. But the fuel cleanli­ness requirements for modern aircraft engines re­quire more extensive testing than this.

One test recommended by the FAA for check­ing for fuel contaminants is to drain about a quart of fuel into a spotlessly clean ten-quart white enamel bucket. Stir the fuel with a clean paddle and swirl it in the form of a vortex cone. All of the contaminants will gather at the centre of the vortex and can be easily seen. A few drops of food colouring will dye any water that is in the fuel so it will be readily visible, but the food colouring will not colour the fuel.

A commercial water test kit is used far more often than the white-bucket test. This kit con­tains a small glass jar and a supply of capsules containing a grayish-white powder, and a 100-cc sample of fuel is taken from the truck and put in­to the jar. Then one of the test capsules is dumped into this fuel, the lid is screwed on, and the contents are shaken for about ten seconds. If the powder changes its colour from gray-white to pink or purple, the fuel has more than 30 parts per million of water, and it is not considered safe for use. It may be pumped through the water traps and filters in the truck and another sample taken. This test is fail-safe, because any error in performing the test will cause it to give an unsafe indication.

If the fuel sample is taken from the aircraft, the fuel should be drawn from the main strainer and some fuel should be allowed to flow from every one of the tanks. Drawing fuel from the main strainer when the tank selector is in the both position will not necessarily get fuel from all of the tanks.

Fire Hazards: when Fuelling and De fuelling Aviation fuels are both highly flammable and volatile, and special care must be exercised when transferring them into or out of an aircraft. Be sure that the proper type of fire extinguisher is available at the aircraft and that it has been pro­perly serviced and has not been used, even par­tially, since it was last serviced.

Never service an aircraft with fuel inside a hangar or in any other closed area. If fuel is stored in containers other than the fuel service truck or the aircraft fuel tanks, be sure that the containers are closed, not only to prevent the en­try of contaminants, but also to prevent the re­lease of fuel vapours.

If any fuel is spilled, wipe it up immediately; or, if too much has been spilled to wipe up, wash it away with water or cover it with sand.

Be sure that there are no open fires, gasoline motor exhausts, or electrical equipment opera­ting in the vicinity of fuelling or defuelling opera­tions, and be sure that all electrical power on the aircraft except that required for the fuelling opera­tion is turned off.

Wear only a type of shoes that will not cause sparks and clothing that will not produce sparks from static electricity. And, be sure that the air­craft and fuel truck or hydrant are properly bond­ed electrically.

Static electricity builds up when fuel flows through the fuel lines and its discharge must be guarded against.) About fifteen minutes is needed for a tank full of fuel, especially turbine fuel, to relax itself of the charges of static electricity after the tank has been filled.

When fuelling or refuelling an aircraft, first connect the fuelling vehicle or fuel cabinet to the aircraft with a static ground wire, and then con­nect the nozzle to the grounding point at the tank filler opening. Only after this has been done should the filler cap be removed.

If a fire does occur, always fight it from up­wind and use a steady sweeping motion at the leading edge of the flames.;. Flammable liquids have a tendency to flash back if they are not suffi­ciently cooled after the flame has been extin­guished.

 Fuelling Procedures: If you are to fuel an aircraft from a fuel truck, approach the aircraft from the front, parallel to the wings, and park the truck in front of the air­craft in such a direction that if it should roll, it cannot possibly roll into the aircraft being ser­viced, or into any other aircraft.

Be sure that only the proper grade of fuel is used. This is extremely important, as servicing an aircraft with the incorrect grade of fuel can cause serious damage to the engine.

Remove the fire extinguisher from the fuel truck and place it where it is immediately accessi­ble. Then connect the static bonding wire be­tween the truck and the aircraft.

If a ladder is used to reach the top of the wing, be sure it is padded so it cannot damage the finish on the wing or the de-icer boots if they are installed. Put a wing mat in place over the wing and connect the bonding wire between the fuel nozzle and the tank, and then remove the fuel tank cap. This is called over-wing fuelling.

De fuelling: When fuel is removed from an aircraft, follow all of the safety procedures required for fuelling, and be sure that all of the fuel removed from the aircraft tanks is returned to the proper fuel truck, or, if it is to be stored in drums or other con­tainers, that these are clean. After they are filled and properly closed, they should be stored in a designated storage area.

Fuel Leakage

When leakage or spillage of fuel has occurred, care must be taken to ensure that all traces of fuel and vapour are removed.    Where lagging has become contaminated with fuel in areas adjacent to passenger cabins and crew com­partments, the lagging should be removed and cleaned, and any residual fuel should be mopped up. Where fuel has leaked into a compartment which is vented and drained, the venting and drainage arrangements should be checked to ensure that they are functioning correctly and that there is a flow of air through the compartment. It is sometimes specified that a check of the venting system of such a compartment should be carried out with the cabin pressurised. In the event of a gross leakage, consideration should be given to the effects that fuel may have on other materials and components, such as cable insulation, seals, transparencies and bearings.