Chapter 11. Safety, Ground Operations, & Servicing

Oxygen Hazards

Gaseous oxygen is chemically stable and is nonflammable. However, combustible materials ignite more rapidly and burn with greater intensity in an oxygenrich atmosphere. In addition, oxygen combines with oil, grease, or bituminous material to form a highly explosive mixture, which is sensitive to compression or impact. Physical damage to, or failure of oxygen containers, valves, or plumbing can result in an explosive rupture, with extreme danger to life and property. It is imperative that the highest standard of cleanliness be observed in handling oxygen and that only qualified and authorized persons be permitted to service aircraft gaseous oxygen systems.

In addition to aggravating the fire hazard, because of its low temperature (it boils at -297 °F), liquid oxygen causes severe “burns" (frostbite) if it comes in contact with the skin.

Fuel Servicing Of Aircraft

Types of Fuel and Identification

Two types of aviation fuel in general use are aviation gasoline, also known as AVGAS, and turbine fuel, also known as JET A fuel.

Aviation gasoline (AVGAS) is used in reciprocatingengine aircraft. Currently, there are three grades of fuel in general use: 80/87, 100/130, and 100LL (low lead). A fourth grade, 115/145, is in limited use in the large reciprocating-engine aircraft. The two numbers indicate the lean mixture and rich mixture octane rating numbers of the specific fuel. In other words, with 80/87 aviation gasoline, the 80 is the lean mixture rating and 87 is the rich mixture rating number. To avoid confusing the types of AVGAS, it is generally identified as grade 80, 100, 100LL, or 115. AVGAS can also be identified by a color code. The color of the fuel should match the color band on piping and fueling equipment.

Turbine fuel/jet fuel is used to power turbojet and turbo-shaft engines. Three types of turbine fuel generally used in civilian aviation are JET A and JET A-1, which are made from kerosene and JET B, which is a blend of kerosene and aviation gasoline. While jet fuel is identified by the color black on piping and fueling equipment, the actual color of jet fuel can be clear or straw colored.

Never mix AVGAS and turbine fuel. Adding jet fuel to AVGAS will cause a decrease in the power developed by the engine and could cause damage to the engine (through detonation) and loss of life. Adding AVGAS to jet fuel, although allowed, can cause lead deposits in the turbine engine and can lead to reduced service life.

Contamination Control

Contamination is anything in the fuel that is not supposed to be there. The types of contamination found in aviation fuel include water, solids, and microbial growths.

The control of contamination in aviation fuel is extremely important, since contamination can lead to engine failure, or stoppage and the loss of life. The best method of controlling contamination is to prevent its introduction into the fuel system. Some forms of contamination will still occur inside the fuel system.

Either way, the filter, separators, and screens should remove most of the contamination.

Water in aviation fuels will generally take two forms: dissolved (vapor) and free water.

The dissolved water is not a major problem until, as the temperature lowers, it becomes free water. This then poses a problem if ice crystals form, clogging filters and other small orifices.

Free water can appear as water slugs or entrained water. Water slugs are concentrations of water. This is the water that is drained after fueling an aircraft.

Entrained water is suspended water droplets. These droplets may not be visible to the eye, but will give the fuel a cloudy look. The entrained water will settle out in time.

Solid contaminants are insoluble in fuel. The more common types are rust, dirt, sand, gasket material, lint, and fragments of shop towels. The close tolerances of fuel controls and other fuel-related mechanisms can be damaged or blocked by particles as small as onetwentieth the diameter of a human hair.

Microbiological growths are a problem in jet fuel. There are a number of varieties of micro-organisms that can live in the free water in jet fuel. Some variations of these organisms are airborne, others live in the soil. The aircraft fuel system becomes susceptible to the introduction of these organisms each time the aircraft is fueled.

Favorable conditions for the growth of micro-organisms in the fuel are warm temperatures and the presence of iron oxide and mineral salts in the water.

The effects of micro-organisms are:

  • Formation of slime or sludge that can foul filters, separators, or fuel controls.
  • Emulsification of the fuel.
  • Corrosive compounds that can attack the fuel tank’s structure. In the case of a wet wing tank, the tank is made from the aircraft’s structure. They can also have offensive odors.

The best way to prevent microbial growth is to keep the fuel dry.

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