Aircraft Systems

Refueling Procedures switch prevents fuel from flowing unless the fan is working. Outside the combustion chamber, a second, larger diameter Static electricity is formed by the friction of air passing tube conducts air around the combustion tube’s outer surface, over the surfaces of an aircraft in flight and by the flow of and a second fan blows the warmed air into tubing to direct fuel through the hose and nozzle during refueling. Nylon, it towards the interior of the aircraft. Most gasoline heaters Dacron, or wool clothing is especially prone to accumulate can produce between 5,000 and 50,000 British Thermal Units and discharge static electricity from the person to the funnel (BTU) per hour. or nozzle. To guard against the possibility of static electricity igniting fuel fumes, a ground wire should be attached to the Fuel fired heaters require electricity to operate and are aircraft before the fuel cap is removed from the tank. Because compatible with a 12-volt and 24-volt aircraft electrical both the aircraft and refueler have different static charges, system. The heater requires routine maintenance, such as bonding both components to each other is critical. By bonding regular inspection of the combustion tube and replacement of both components to each other, the static differential charge is the igniter at periodic intervals. Because gasoline heaters are equalized. The refueling nozzle should be bonded to the aircraft required to be vented, special care must be made to ensure the before refueling begins and should remain bonded throughout vents do not leak into the interior of the aircraft. Combustion the refueling process. When a fuel truck is used, it should be byproducts include soot, sulfur dioxide, carbon dioxide, and grounded prior to the fuel nozzle contacting the aircraft. some carbon monoxide. An improperly adjusted, fueled, or poorly maintained fuel heater can be dangerous. If fueling from drums or cans is necessary, proper bonding and grounding connections are important. Drums should be Exhaust Heating Systems placed near grounding posts, and the following sequence of Exhaust heating systems are the simplest type of aircraft connections observed: heating system and are used on most light aircraft. Exhaust 1. Drum to ground heating systems are used to route exhaust gases away from 2. Ground to aircraft the engine and fuselage while reducing engine noise. The exhaust systems also serve as a heat source for the cabin 3. Drum to aircraft or nozzle to aircraft before removing and carburetor. the fuel cap The risks of operating an aircraft with a defective exhaust When disconnecting, reverse the order. heating system include carbon monoxide poisoning, a decrease in engine performance, and an increased potential The passage of fuel through a chamois increases the charge for fire. Because of these risks, technicians should be aware of static electricity and the danger of sparks. The aircraft of the rate of exhaust heating system deterioration and should must be properly grounded and the nozzle, chamois filter, thoroughly inspect all areas of the exhaust heating system to and funnel bonded to the aircraft. If a can is used, it should look for deficiencies inside and out. be connected to either the grounding post or the funnel. Under no circumstances should a plastic bucket or similar Combustion Heater Systems nonconductive container be used in this operation. Combustion heaters or surface combustion heaters are often used to heat the cabin of larger, more expensive aircraft. Heating System This type of heater burns the aircraft’s fuel in a combustion There are many different types of aircraft heating systems that chamber or tube to develop required heat, and the air are available depending on the type of aircraft. Regardless of flowing around the tube is heated and ducted to the cabin. which type or the safety features that accompany them, it is A combustion heater is an airtight burner chamber with a always important to reference the specific aircraft operator’s stainless-steel jacket. Fuel from the aircraft fuel system is manual and become knowledgeable about the heating system. ignited and burns to provide heat. Ventilation air is forced Each has different repair and inspection criteria that should over the airtight burn chamber picking up heat, which is then be precisely followed. dispersed into the cabin area. Fuel Fired Heaters When the heater control switch is turned on, airflow, ignition, A fuel fired heater is a small mounted or portable space- and fuel are supplied to the heater. Airflow and ignition are heating device. The fuel is brought to the heater by using constant within the burner chamber while the heater control piping from a fuel tank, or taps into the aircraft’s fuel system. switch is on. When heat is required, the temperature control A fan blows air into a combustion chamber, and a spark plug is advanced, activating the thermostat. The thermostat (which or ignition device lights the fuel-air mixture. A built-in safety 7-29