Flow divider (reciprocating engine).  The valve in an RSA  fuel injection system that divides the fuel from the fuel control  unit and distributes it to all of the cylinders. It compares with  the manifold valve in a Teledyne-Continental fuel injection  system. Gauge pressure.  Pressure referenced from existing  atmospheric pressure. Gas generator.  The basic gas turbine engine. It consists of  the compressor, diffuser, combustor, and turbine. The gas  generator is also called the core engine. Flow divider (turbine engine).  A component in a turbine  engine fuel system that routes all of the fuel to the primary  nozzles or primary orifices when starting the engine or when  the rpm is low. When the engine speed builds up, the flow  divider shifts and opens a passage to send the majority of the  fuel to the secondary nozzles or orifices. Gas turbine engine.  An internal combustion engine that  burns its fuel in a constant-pressure cycle and uses the  expansion of the air to drive a turbine which, in turn, rotates  a compressor. Energy beyond that needed to rotate the  compressor is used to produce torque or thrust. FMC. Flight management computer.  An electronic flight  instrumentation system that enables the flight crew to initiate  and implement a given flight plan and monitor its execution. General Aviation Airworthiness Alerts.  While these  documents are no longer published, they are still available at  www.faa.gov. These are used to alert technicians of problems  that have been found in specific models of aircraft, and  reported on Malfunction and Defect Reports. Airworthiness  Alerts suggest corrective action, but compliance with the  suggestion is not mandatory. FOD.  Foreign object damage. Damage to components in  the gas path of a turbine engine, caused by ingested objects.  Debris from the runway or ramp cause FOD on the ground.  Ice and birds cause most in-flight FOD. general aviation.  A term used to describe the total field of  aviation operation except the military and airlines. Four-stroke cycle.  A constant-volume cycle of energy  transformation that has separate strokes for intake,  compression, power, and exhaust. Geometric pitch.  The distance a propeller would advance  in one revolution if it were rotating in a solid. Fractional distillation.  Procedure used for separating  various components from a physical mixture of liquids. Crude  oil is a mixture of many different types of hydrocarbon fuels  which can be separated by carefully raising its temperature.  The first products to be released, those having the lowest  boiling points, are some of the gaseous fuels; next are  gasoline, kerosene, diesel fuel, heavy fuel oils, lubricating  oils, and finally, tar and asphalt. Geopotential of the tropopause.  The point in the standard  atmosphere where the temperature stops dropping and  becomes constant. This is the tropopause, or the dividing line  between the troposphere and the stratosphere. Frangible.  Capable of being broken. Free-turbine engine.  A gas turbine engine with a turbine  stage on a shaft independent of the shaft used to drive the  compressor. Free turbines are used to drive the propeller  reduction gear in a turboprop engine and the rotor  transmission in a helicopter. Gerotor pump.  A form of constant-displacement pump  that uses an external-tooth drive gear that meshes with and  drives an internal-tooth gear that has one more space for a  tooth than there are teeth on the drive gear. Both gears turn  inside a close-tolerance housing. As the gears rotate, fluid  flows between the teeth that are beginning to un-mesh, and  is carried around the pump as the space continues to open  up. On the discharge side of the pump, the teeth becomes  smaller, fluid is forced out of the pump. Glass cockpit.  An aircraft instrument system that uses a few  color cathode-ray-tube displays to replace a large number of  mechanically actuated instruments. Governor.  A control used to automatically change the pitch  of a constant speed propeller to maintain a constant engine  rpm as air loads vary in flight. GPU.  Ground power unit. A service component used to  supply electrical power and compressed air to an aircraft  when it is operating on the ground. Freezing point.  The temperature at which solids, such as  wax crystals, separate from a hydrocarbon fuel as it is cooled. Fuel-air mixture ratio.  Ratio of the number of pounds of  fuel to the number of pounds of air in the mixture burned in  cylinders of a reciprocating engine. Full-register position.  The position of a magnet in a  magneto when its poles are aligned with the pole shoes and  the maximum amount of magnetic flux is flowing through  the magnetic circuit. G-13