Aft-fan engine.  A turbofan engine with the fan mounted  behind the compressor section. The blades of an aft-fan are  normally extensions of the free turbine blades. Afterburner.  A component in the exhaust system of a  turbojet or turbofan engine used to increase the thrust for  takeoff and for special flight conditions. Since much of the air  passing through a gas turbine engine is used only for cooling,  it still contains a great deal of oxygen. Fuel is sprayed into  the hot, oxygen-rich exhaust in the afterburner, where it is  ignited and burned to produce additional thrust. Air bleed (carburetor component).  A small hole in the fuel  passage between the float bowl and the discharge nozzle of  a float carburetor. Air drawn into the liquid fuel through the  air bleed breaks the fuel up into an emulsion, making it easy  to atomize and vaporize. Air cooling.  The removal of unwanted heat from an aircraft  engine by transferring the heat directly into the air flowing  over the engine components. Air-fuel mixture ratio.  The ratio of the weight of the air  to that of the fuel in the mixture fed into the cylinders of  an engine. Air impingement starter.  A turbine engine starter that  basically consists of a nozzle that blows a stream of  compressed air against the turbine blades to rotate the  compressor for starting the engine. Air-oil separator.  A component in a turbine engine  lubrication system that removes the air from the scavenged  oil before it is returned to the oil tank. Airworthiness Directive.  Airworthiness Directives (ADs)  are legally enforceable regulations issued by the FAA  in accordance with 14 CFR part 39 to correct an unsafe  condition in a product. Part 39 defines a product as an aircraft,  engine, propeller, or appliance All-weather spark plug.  A shielded spark plug designed for  high altitude operation. The ceramic insulator is recessed into  the shell to allow a resilient grommet on the ignition harness  to provide a watertight seal. All weather spark plugs, also  called high-altitude spark plugs, are identified by their 3/4- 20 shielding threads. Alpha control range (alpha mode).  The flight operating  mode from takeoff through landing for a turbo-prop engine.  Alpha mode includes operations from 95% to 100% of the  engine’s rated rpm. Anodizing.  A hard, airtight, unbroken oxide film  electrolytically deposited on an aluminum alloy surface to  protect it from corrosion. Annunciator panel.  A panel of warning lights visible to the  flight crew. The lights are identified by the name of the system  they represent and are often covered with colored lenses. Red  lights indicate a dangerous condition and green indicate a  safe condition. Annulus.  A ring or groove around the outside of a circular  body or shaft, or around the inside of a cylindrical hole. Annular orifice.  A ring-shaped orifice, normally one that  surrounds another orifice. Annular duct.  A duct, or passage, that surrounds an object.  The annular fan-discharge duct surrounds the core engine. Annual inspection.  A complete inspection of the airframe  and powerplant required for FAA-certificated aircraft  operating under 14 CFR part 91 General Operating and Flight  Rules, and not on one of the authorized special inspection  programs. An annual inspection must be conducted every  12 calendar months, and it must be conducted by an  aviation maintenance technician who holds an Airframe  and Powerplant rating and an Inspection Authorization.  The scope of an annual inspection is the same as that of a  100-hour inspection.  Angle of attack.  The acute angle between the chord line of  a propeller blade and the relative wind. The angle of attack  is affected by both the engine rpm and the forward speed of  the aircraft.  Analog indicator.  An indicator that shows the value of  the parameter being measured by a number marked on a  graduated dial aligned with a movable pointer. Ambient air pressure.  The pressure of the air that surrounds  an object. Amateur-built aircraft.  Aircraft built by individuals as  a hobby rather than by factories as commercial products.  Amateur-built or homebuilt aircraft do not fall under the  stringent requirements imposed by the FAA on commercially  built aircraft. Altitude engine.  An aircraft reciprocating engine equipped  with a supercharger that allows it to maintain its rated sea- level horsepower to an established higher altitude.  G-2