Aircraft Servicing and Fueling

1-20 performed in accordance with applicable local regulations. control towers to control and expedite the taxiing of aircraft. The following section provides detailed instructions on taxi signals and related taxi instructions. Taxi Signals Many ground accidents have occurred as a result of improper technique in taxiing aircraft. Although the pilot is ultimately responsible for the aircraft until the engine is stopped, a taxi signalman can assist the pilot around the flight line. In some aircraft configurations, the pilot’s vision is obstructed while on the ground. The pilot cannot see obstructions close to the wheels or under the wings and has little idea of what is behind the aircraft. Consequently, the pilot depends upon the taxi signalman for directions. Figure 1-23 shows a taxi signalman indicating his readiness to assume guidance of the aircraft by extending both arms at full length above his head, palms facing each other.

The standard position for a signalman is slightly ahead of and in line with the aircraft’s left wingtip. As the signalman faces the aircraft, the nose of the aircraft is on the left. [Figure 1-24] The signalman must stay far enough ahead of the wingtip to remain in the pilot’s field of vision. It is a good practice to perform a foolproof test to be sure the pilot can see all signals. If the signalman can see the pilot’s eyes, the pilot can see the signals. published in the Federal Aviation Administration (FAA) Aeronautical Information Manual (AIM). There are other standard signals, such as those published in Advisory Circular 00-34, as revised, and by the International Standards (ICAO) Annex 2, Appendix 1 and the Armed Forces. Furthermore, operation conditions in many areas may call for a modified set of taxi signals. The signals shown in Figure 1-24 represent a minimum number of the most commonly used signals.

Whether this set of signals or a modified set is used is not the most important consideration, as long as each flight operational center uses a suitable, agreed-upon set of signals. helicopter operating signals. The taxi signals to be used must be studied until the taxi signalman can execute them clearly and precisely. The signals are to be given in such a way that the pilot cannot confuse their meaning. Remember that the pilot receiving the signals is always some distance away and often look out and down from a difficult angle. Thus, the signalman’s hands must be kept well separated, and signals are to be over-exaggerated rather than risk making indistinct signals. If there is any doubt about a signal, or if the pilot does not appear to be following the signals, use the “stop” sign and begin the series of signals again.

The signalman is to always try to give the pilot an indication of the approximate area that the aircraft is to be parked. The signalman must glance behind himself or herself often when walking backward to prevent backing into a propeller or tripping over a chock, fire bottle, tie-down line, or other obstruction. Taxi signals are usually given at night with the aid of illuminated wands attached to flashlights. [Figure 1-26] Night signals are made in the same manner as day signals with the exception of the stop signal. The stop signal used at night is the “emergence stop” signal. This signal is made by crossing the wands to form a lighted “X” above and in front of the head.

Servicing Aircraft

Servicing Aircraft Air/Nitrogen Oil & Fluids Checking or servicing aircraft fluids is an important maintenance function. Before servicing any aircraft, consult the specific aircraft maintenance manual to determine the proper type of servicing equipment and procedures. In general, aircraft engine oil is checked with a dipstick or a sight gauge. There are markings on the stick or around the sight gauge to determine the correct level. Reciprocating engines are to be checked after the engine has been inactive, while the turbine engine must be checked just after shutdown. Dry sump oil systems tend to hide oil that has seeped from the oil tank into the gearcase of the engine. This oil does not show up on the dipstick until the engine has been started or motored.

If serviced before this oil is pumped back into the tank, the engine overfills. Never overfill the oil tank. Oil foams as it is circulated through the engine. The expansion space in the oil tank allows for this foaming (oil mixing with air). Also the correct type of oil must be used for the appropriate engine being serviced. Hydraulic fluid, fuel, and oil, if spilled on clothes or skin, must be removed as soon as possible because 1-21 Lights Meaning Flashing green Cleared to taxi Steady red Stop Flashing red Taxi clear of runway in use Flashing white Return to starting point Alternating red and green Exercise extreme caution of fire danger and health reasons.

When servicing a hydraulic reservoir, the correct fluid must be used. Normally, this can be determined by the container or by color. Some reservoirs are pressurized by air that must be bled off before servicing. Efforts must be made to prevent any type of contamination during servicing. Also, if changing hydraulic filters, assure that the pressure is off the system before removing the filters. After servicing the filters (if large amounts of fluids were lost) or system quantity, air must be purged and the system checked for leaks. While servicing tires or struts with high-pressure nitrogen, the technician must use caution while performing maintenance. Clean areas before connecting filling hose and do not overinflate.

Ground Support Equipment

Electric Ground Power Units Ground support electrical APUs vary widely in size and type. However, they can be generally classified by towed, stationary, or self-propelled items of equipment. Some units are mainly for in-hangar use during maintenance. Others are designed for use on the flight line, either at a stationary gate area or towed from aircraft to aircraft. The stationary type can be powered from the electrical service of the facility. The movable type ground power unit (GPU) generally has an onboard engine that turns a generator to produce power. Some smaller units use a series of batteries. The towed power units vary in size and range of available power.

The smallest units are simply high-capacity batteries used to start light aircraft. These units are normally mounted on wheels or skids and are equipped with an extra-long electrical line terminated in a suitable plug-in adapter. Larger units are equipped with generators. Providing a wider range of output power, these power units are normally designed to supply constant-current, variable voltage DC electrical power for starting turbine aircraft engines and constant-voltage DC for starting reciprocating aircraft engines. Normally somewhat top-heavy, large towed power units are towed at restricted speeds, and sharp turns are avoided. An example of a large power unit is shown in Self-propelled power units are normally more expensive than the towed units and, in most instances, supply a wider range of output voltages and frequencies. The stationary power unit, shown in Figure 1-28, is capable of supplying DC power in varying amounts, as well as 115/200-volt, 3-phase, 400-cycle AC power continuously for 5 minutes.

When using ground electrical power units, it is important to position the unit to prevent collision with the aircraft being serviced, or others nearby, in the event the brakes on the unit fail. It must be parked so that the service cable is extended to near its full length away from the aircraft being serviced, but not so far that the cable is stretched or undue stress is placed on the aircraft electrical receptacle. Observe all electrical safety precautions when servicing an aircraft. Additionally, never move a power unit when service cables are attached to an aircraft or when the generator system is engaged.

1-22 Start engines Slow down Flagman directs pilot to signalman if traffic conditions require Stop Come ahead Emergency stop Cut engines Pull chocks Insert chocks All clear (O.K.) Left turn Right turn Night operation Signalman directs towingSignalman's position Hydraulic Ground Power Units Portable hydraulic test stands are manufactured in many sizes and cost ranges. [Figure 1-29] Some have a limited range of operation, while others can be used to perform all the system tests that fixed-shop test stands are designed to perform. Hydraulic power units, sometimes called a hydraulic mule, provide hydraulic pressure to operate the aircraft systems during maintenance. They can be used to: • Drain the aircraft hydraulic systems.

• Filter the aircraft hydraulic system fluid. • Refill the aircraft hydraulic system with clean fluid. • Check the aircraft hydraulic systems for operation and leaks. This type of portable hydraulic test unit is usually an electrically-powered unit. It uses a hydraulic system 1-23 Take off Go down Move back Move forward Move right Move left Landing direction Go up Swing tail to right Swing tail to left StopEngage rotorStart engine Stop rotor capable of delivering a variable volume of fluid from zero to approximately 24 gallons per minute at variable pressures up to 3,000 psi. Operating at pressures of 3,000 psi or more, extreme caution must be used when operating hydraulic power units. At 3,000 psi, a small stream from a leak can cut like a sharp knife.

Therefore, inspect lines used with the system for cuts, frays, or any other damage, and keep them free of kinks and twists. When not in use, hydraulic power unit lines are to be stored (preferably wound on a reel) and kept clean, dry, and free of contaminants. Ground Support Air Units Air carts are used to provide low-pressure (up to 50 psi high volume flow) air that can be used for starting the engines and heating and cooling the aircraft on the ground (using the onboard aircraft systems). It generally consists of an APU 1-24 built into the cart that provides bleed air from the APU’s compressor for operating aircraft systems or starting engines.

[Figure 1-30] Ground Air Heating and Air Conditioning Most airport gates have facilities that can provide heated or cooled air. The units that cool or heat the air are permanent installations that connect to the aircraft’s ventilation system by use of a large hose. Portable heating and air conditioning units can also be moved close to the aircraft and connected by a duct that provides air to keep the cabin temperature comfortable. Oxygen Servicing Equipment Before servicing any aircraft, consult the specific aircraft maintenance manual to determine the proper types of servicing equipment to be used. Two personnel are required to service an aircraft with gaseous oxygen. One person is stationed at the control valves of the servicing equipment, and one person is stationed where they can observe the pressure in the aircraft system. Communication between the two people is required in the event of an emergency.

Do not service aircraft with oxygen during fueling, defueling, or other maintenance work that could provide a source of ignition. Oxygen servicing of aircraft is to be accomplished outside hangars. Oxygen used on aircraft is available in two types: gaseous and liquid. The type to use on any specific aircraft depends on the type of equipment in the aircraft. Gaseous oxygen is stored in large steel cylinders, while liquid oxygen (commonly referred to as LOX) is stored and converted into a usable gas in a liquid oxygen converter. Oxygen is commercially available in three general types: aviator’s breathing, industrial, and medical. Only oxygen marked “Aviator’s Breathing Oxygen” that meets Federal Specification BB-0-925A, Grade A, or its equivalent is to be used in aircraft breathing oxygen systems. Industrial oxygen may contain impurities that could cause the pilot, crew, and/ or passengers to become sick. Medical oxygen, although pure, contains water that can freeze in the cold temperatures found at the altitudes where oxygen is necessary.

1-25 Oxygen Hazards Gaseous oxygen is chemically stable and is nonflammable. However, combustible materials ignite more rapidly and burn with greater intensity in an oxygen-rich atmosphere. In addition, oxygen combines with oil, grease, or bituminous material to form a highly-explosive mixture that 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 and 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 A VGAS, and turbine fuel, also known as JET A fuel. Aviation gasoline (A VGAS) is used in reciprocating engine 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 A VGAS, the 80 is the lean mixture rating and 87 is the rich mixture rating number. To avoid confusing the types of A VGAS, it is generally identified as grade 80, 100, 100LL, or 115. A VGAS can also be identified by a color code. The color of the fuel needs to match the color band on piping and fueling equipment. [Figure 1-31] 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, made from kerosene, and JET B, a blend of kerosene and A VGAS.

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. Before mixing A VGAS and turbine fuel, refer to the Type Certificate Data Sheet for the respective powerplant. Adding jet fuel to A VGAS causes a decrease in the power developed by the engine and could cause damage to the engine (through detonation) and loss of life. Adding A VGAS to jet fuel 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 can still occur inside the fuel system.

However, the filter, separators, and screens remove most of the contamination. Water in aviation fuels 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. 1-26 Color Grade Red 80 Green 100 Blue 100LL Purple 115 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 give the fuel a cloudy look. The entrained water settles 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 1⁄20 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 best way to prevent microbial growth is to keep the fuel dry.

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. Fueling Hazards The volatility of aviation fuels creates a fire hazard that has plagued aviators and aviation engine designers since the beginning of powered flight. V olatility is the ability of a liquid to change into a gas at a relatively low temperature. In its liquid state, aviation fuel does not burn. It is, therefore, the vapor or gaseous state that the liquid fuel changes that is not only useful in powering the aircraft, but also a fire hazard.

Static electricity is a byproduct of one substance rubbing against another. Fuel flowing through a fuel line causes a certain amount of static electricity. The greatest static electricity concern around aircraft is that during flight, the aircraft moving through the air causes static electricity to build in the airframe. If that static electricity is not dissipated prior to refueling, the static electricity in the airframe attempts to return to the ground through the fuel line from the servicing unit. The spark caused by the static electricity can ignite any vaporized fuel. Breathing the vapors from fuel can be harmful and must be limited. Any fuel spilled on the clothing or skin must be removed as soon as possible.

Fueling Procedures The proper fueling of an aircraft is the responsibility of the owner/operator. This does not, however, relieve the person doing the fueling of the responsibility to use the correct type of fuel and safe fueling procedures. There are two basic procedures when fueling an aircraft. Smaller aircraft are fueled by the over-the-wing method. This method uses the fuel hose to fill through fueling ports on the top of the wing. The method used for larger aircraft is the single point fueling system. This type of fueling system uses receptacles in the bottom leading edge of the wing to fill all the tanks. This decreases the time it takes to refuel the aircraft, limits contamination, and reduces the chance of static electricity igniting the fuel. Most pressure fueling systems consist of a pressure fueling hose and a panel of controls and gauges that permit one person to fuel or defuel any or all fuel tanks of an aircraft. Each tank can be filled to a predetermined level. These procedures are illustrated in Figures 1-32 and 1-33.

Prior to fueling, the person fueling must check the following: 1. Ensure all aircraft electrical systems and electronic devices, including radar, are turned off. 2. Do not carry anything in the shirt pockets. These items could fall into the fuel tanks. 3. Ensure no flame-producing devices are carried by anyone engaged in the fueling operation. A moment of carelessness could cause an accident. 4. Ensure that the proper type and grade of fuel is used. Do not mix A VGAS and JET fuel. 5. Ensure that all the sumps have been drained. 6. Wear eye protection. Although generally not as critical as eye protection, other forms of protection, such as rubber gloves and aprons, can also protect the skin from the effects of spilled or splashed fuel.

1-27 Ground wire 7. Do not fuel aircraft if there is danger of other aircraft in the vicinity blowing dirt in the direction of the aircraft being fueled. Blown dirt, dust, or other contaminants can enter an open fuel tank, contaminating the entire contents of the tank. 8. Do not fuel an aircraft when there is lightning within 5 miles. 9. Do not fuel an aircraft within 500 feet of operating ground radar. When using mobile fueling equipment: 1. Approach the aircraft with caution, positioning the fuel truck so that if it is necessary to depart quickly, no backing needed. 2. Set the hand brake of the fuel truck, and chock the wheels to prevent rolling.

3. Ground the aircraft and then ground the truck. Next, ground or bond them together by running a connecting wire between the aircraft and the fuel truck. This may be done by three separate ground wires or by a “Y” 1-28 cable from the fuel truck. 4. Ensure that the grounds are in contact with bare metal or are in the proper grounding points on the aircraft. Do not use the engine exhaust or propeller as grounding points. Damage to the propeller can result, and there is no way of quickly ensuring a positive bond between the engine and the airframe. 5. Ground the nozzle to the aircraft, then open the fuel tank.

6. Protect the wing and any other item on the aircraft from damage caused by spilled fuel or careless handling of the nozzle, hose, or grounding wires. 7. Check the fuel cap for proper installation and security before leaving the aircraft. 8. Remove the grounding wires in the reverse order. If the aircraft is not going to be flown or moved soon, the aircraft ground wire can be left attached. When fueling from pits or cabinets, follow the same procedures as when using a truck. Pits or cabinets are usually designed with permanent grounding, eliminating the need to ground the equipment. However, the aircraft still must be grounded, and then the equipment must be grounded to the aircraft as it was with mobile equipment.

Defueling Defueling procedures differ with different types of aircraft. Before defueling an aircraft, check the maintenance/service manual for specific procedures and cautions. Defueling can be accomplished by gravity defueling or by pumping the fuel out of the tanks. When the gravity method is used, it is necessary to have a method of collecting the fuel. When the pumping method is used, care must be taken not to damage the tanks, and the removed fuel cannot be mixed with good fuel. General precautions when defueling are: • Ground the aircraft and defueling equipment. • Turn off all electrical and electronic equipment.

• Have the correct type of fire extinguisher available. • Wear eye protection.