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EAA's Learn to Fly Newsletter
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Aviation Glossary

Adjustable stabilizer – a kind of horizontal stabilizer that can be adjusted in flight to trim the airplane, thereby allowing the airplane to fly hands-off at any given airspeed.

Adverse Yaw - Yaw generated when the ailerons are used. The lifting wing generates more drag, causing an airplane to yaw (or turn) toward it.

AGL - (Above Ground Level) Altitude expressed as feet above the ground or terrain. It is usually set to indicate the airport field elevation during the pre-takeoff checklist.

Airframe – the structure of an aircraft without the powerplant. It is generally considered to consist of five principle units – the fuselage, wings, stabilizers, flight control surfaces, and landing gear.

Airspeed Indicator - An instrument or device that measures the airspeed of an aircraft through an air mass but not its groundspeed.

Altimeter - An adjustable cockpit instrument used to measure an aircraft’s altitude.

Altimeter Setting - A reference setting on the altimeter so that the instrument indicates an accurate altitude.

Axial - Motion along a real or imaginary straight line on which an object supposedly or actually rotates.

Back pressure – The pressure caused by a reciprocating engine’s exhaust system that opposes the burned gases discharged from the engine’s cylinders.

Balloon – lighter-than-air non-steerable aircraft that is not engine driven. Its rising capability comes from gases or hot air that is used to fill the bag.

Bay - Any specific compartment in the body of the aircraft. It may also refer to a portion of a truss, or fuselage, between adjacent bulkheads, struts or frame positions.

Bench check – a functional check performed on a part that has been removed from an aircraft to determine its condition of serviceability. The equipment is set up on a test bench and operated to find out whether or not it is functioning as it should.

Biplane – An airplane having two wings, one placed above the other.

Blade Angle – The angle between the plane of propeller rotation and the face of the
propeller blade.

Boundary layer – the layer of air immediately adjacent to the surface of an airfoil. Its flow, rather than being laminar, is essentially random, or circulatory, and produces a great deal of aerodynamic drag.

Carburetor – consists of a main air passage through which the engine draws its supply of air, a mechanism to control the quantity of fuel discharged in relation to the flow of air, and a means of regulating the quantity of fuel/air mixture delivered to the engine cylinders.

Center of Gravity (CG) - The longitudinal and lateral point in an aircraft where it is stable; the static balance point.

Class A Airspace - Airspace between 18,000 and 60,000 feet MSL (Mean Seal Level) over the contiguous United States. IFR clearances are required for all aircraft operating in Class A airspace.

Class B Airspace - Airspace area around the busiest U.S. hub airports (i.e. Chicago O’Hare), typically to a radius of 20 nautical miles and up to 10,000 feet AGL (Above Ground Level). Operations within Class B airspace require an ATC clearance (Air Traffic Control) and at least a Private Pilot certificate (local waivers are available), radio communications, and an altitude-reporting transponder (Mode C).

Class C Airspace - Airspace area around busy U.S. airports (other than Class B). Radio contact with approach control is mandatory for all traffic. Typically it includes an area from the surface to 1,200 feet AGL out to 5 miles and from 1,200 to 4,000 feet AGL to 10 miles from the airport.

Class D Airspace - Airspace around an airport with an operating control tower; typically to a radius of 5 miles and from the surface to 2,500 feet AGL. Radio contact with the control tower is required prior to entry.

Class E Airspace - General controlled airspace comprising control areas, transition areas, Victor airways, the Continental Control Area, etc.

Class G Airspace - Uncontrolled airspace, generally the airspace from the surface up to 700 feet or 1,200 feet AGL in most of the U.S., but up to as high as 14,500 feet in some remote Western mountainous and sparsely populated areas.

Controlled Airspace - A generic term including all airspace classes in which ATC services are available. VFR aircraft may operate without ATC contact in most controlled airspace as long as weather conditions will permit them to see and avoid other aircraft.

Conventional Gear – Having two main landing wheels at the front and a tail wheel at the rear (as opposed to a “tricycle gear” with two mains and front or nose wheel.) Conventional gear aircraft are popularly called ”taildraggers”. A Piper J-3 Cub is an example of this.

Common Traffic Advisory Frequency (CTAF) - A communications radio frequency designed for the purpose of carrying out airport advisory practices while operating to or from an airport without an operating control tower. The CTAF may be a UNICOM, MULTICOM, flight service station, or tower frequency and is identified in appropriate aeronautical publications and on all visual flight rules (VFR) sectional maps.

Coriolis Force - The force that is produced when a particle moves a long a path in a plane while the plane itself is rotating.

Data plate – a permanent identification plate affixed to an aircraft, engine, or component.

Detonation – The almost instantaneous release of heat energy from fuel in an engine caused by the fuel-air mixture reaching its critical pressure and temperature. It is an explosion rather than a smooth burning process.


Dial indicator
– A precision linear measuring instrument whose indication is much amplified and is read on a circular dial.

Differential pressure - A difference between two pressures. The measurement of airspeed is an example of the use of a differential pressure.

Dimpling – a process that is used to indent the hole into which a flush rivet is to be installed.

Effective pitch – The actual distance a propeller moves through the air in one revolution. It is the difference between the geometric pitch of the propeller and the prop slip.

Elevator – A horizontal, movable control surface on the tail of an airplane that changes its pitch and therefore, angle of attack.

Empennage - An aircraft’s tail group including the rudder, vertical fin, stabilizers and elevators.

Empty weight – the weight of the structure of an aircraft, its powerplant, and all of the fixed equipment.

Fairing – A smooth covering over a joint or a junction in an aircraft structure to provide a smooth surface for the airflow. Its primary purpose is to reduce drag.

FAR PART 61 - The section or part of the Federal Aviation Regulations (FARs) covering pilot certification and standard flight school operations. FAR PART 61, Sub Part J, outlines in detail all requirements that need to be met by a sport pilot candidate.

FAR PART 91 - The section or part of the Federal Aviation Regulations (FARs) covering the flight rules and regulations pertaining to non-commercial flight operations. FAR PART 91 provides you with the “rules of the sky” that you must comply with to operate as a safe non-commercial pilot.

FBO (Fixed Base Operator) - An airport-based business that parks, services, fuels, and may repair aircraft; often rents aircraft and provides flight training. The term was coined to differentiate FBOs from businesses or individuals without an established place of business on the airport.

Flap - A movable, usually hinged airfoil set in the trailing edge of an aircraft wing, designed to increase lift or drag by changing the camber of the wing or used to slow an aircraft during landing by increasing lift.

Flight Envelope - An aircraft’s performance limits, specifically the curves of speed plotted against other variables to indicate the limits of speed, altitude, and acceleration that a particular aircraft cannot safely exceed.

Fuel pressure gage – a gage that indicates the pressure at which fuel is delivered to the carburetor.

Fuselage – The body of an airplane. That part to which the wing, tail, and landing gear attach, and which, in a single-engine airplane, usually carries the engine.

Gear indicators – a device in the cockpit of an airplane with a retractable landing gear to inform the pilot of the condition of the wheels. It indicates whether they are down and locked, in transit, or up and locked.

General Aviation - The 92 percent of U.S. aircraft and more than 65 percent of U.S. flight hours flown by other than major and regional airlines or the military. Often misunderstood as only small, propeller-driven aircraft. Even a large jet or cargo plane operated under certain federal rules can be a general aviation aircraft.

Gross Weight - The total weight of an aircraft when fully loaded, sometimes referred to as takeoff weight. The aircraft manufacturer, through testing and certification, determines gross weight for the aircraft.

Ground Speed – The actual speed that an aircraft travels over the ground (its “shadow speed”); it combines the aircraft’s airspeed and the wind velocity relative to the aircraft’s direction of flight.

Hangar - A building that is used for the purpose of housing and maintaining aircraft.

Hard landing – An improper landing of an aircraft that has transmitted undue stresses into the structure.

Head wind – A wind that is blowing in the opposite direction the aircraft is flying, thereby impeding its forward airspeed.

Heat load – the amount of heat that the air conditioner is required to remove from an airplane cabin in order to maintain a constant cabin temperature.

High-wing airplane – a monoplane with the single supporting surface mounted on top of the fuselage.

Indicated airspeed - Airspeed as indicated on the airspeed indicator with no corrections applied.

Inertia Force – A force due to inertia, or the resistance to acceleration or deceleration.

Inspection Authorization – An authorization issued by the FAA to experienced A&P technicians meeting certain requirements. This authorization allows them to return aircraft to service after annual inspections or certain major repairs.

Instrument – a device to show visually or aurally the attitude, altitude, or operation of an aircraft or aircraft part. It includes the electronic devices used for automatically controlling an aircraft in flight.

Interphone System – A communication system normally carried out between in-flight crewmembers using microphones and earphones.

Jet A – A kerosene-type turbine engine fuel similar to the military JP-5. It has very low vapor pressure and a relatively high flash point.

Jet propulsion – that form of propulsion produced when a relatively small mass of air is given a large amount of acceleration.

Jumbo jets – the name given to wide-bodied airplanes such as the Boeing 747, 757, McDonald Douglas DC-10, Lockheed L-1011, and the A-300 Airbus, etc.

Knock – A loud banging noise made inside a reciprocating engine cylinder during the compression stroke. The knock is an explosion rather than a smooth burning process, and is caused by the almost instantaneous release of heat energy from fuel in an aircraft engine caused by the fuel air mixture reaching its critical pressure and temperature.

Knot - (Nautical mile per hour) The most common measure of aircraft speed. 100 knots is equal to 115 miles per hour. (For miles per hour, multiply knots by 1.15.)

Kreuger flap - A type of leading edge wing flap hinged at the bottom side of the airfoil. When it is actuated, the leading edge bends downward, increasing the overall wing camber which allows the wing to develop additional lift at lower airspeeds.

Landing flaps – a secondary control surface built into the wing by which the overall wing area, or lift-drag ratio, can be increased. The increased wing area permits a slower landing speed. The increased drag reduces airspeeds on landing and shortens the afterlanding roll.

Landing gear – The wheels, floats, skis, and all of the attachments that support the airplane when it is resting on the ground or water.

Landing roll – the distance an aircraft travels on the ground after touchdown to the point it can be stopped or exits to the taxiway.

Leading edge flap – a portion of the leading edge of an airplane wing which folds downward to increase the camber of the wing to increase both its lift and drag. Leading-edge flaps are extended for takeoffs and landings to increase the amount of aerodynamic lift that is produced at any given airspeed.

Longeron – the main longitudinal strength-carrying member of an aircraft fuselage or engine nacelle.

Maintenance manual – A manual produced by the manufacturer of an aircraft, aircraft engine, or component that details the approved methods of maintenance.

Major overhaul – the complete disassembly, cleaning, inspection, repair, and reassembly of an aircraft, engine, or other component of an aircraft in accordance with the manufacturers specifications, and which will return the device to a serviceable condition.

Maximum takeoff weight – The maximum weight of any aircraft on takeoff without exceeding its load factor. (MTOW)

Nautical Mile - The most common distance measurement in aviation. A nautical mile is equivalent to 1.15 statute (standard U.S.) miles.

Navigation lights – lights on the aircraft consisting of a red light on the left wing, a green light on the right wing, and a white light on the tail. FARs require that these lights be displayed in flight during the hours of darkness.

N-Numbers - Federal government aircraft registration numbers. U.S. registered aircraft numbers begin with “N” (example: N23299F).

Nontowered Airport - An airport without a control tower - the majority of America’s 13,000 airports. Only 680 airports have control towers. Nontowered airports are far from being uncontrolled. Pilots follow traffic pattern procedures and self-announce positions and intentions using the common traffic advisory frequency (CTAF), usually called the UNICOM frequency.

Octane rating - The rating system of aviation gasoline with regard to its antidetonating qualities. Fuel with an octane rating of 87 is made up of a mixture of 87% isooctane and 13% heptane.

Overhang - the distance from the outer strut attachment to the tip of the wing.

Overload – to apply a load in excess of that for which a device or structure is designed.

Overspeed Condition - A condition of the propeller operating system in which the propeller is operating above the RPM for which the governor control is set. This causes the propeller blades to be in a lower angle than that required for constant speed operation.

Pancake landing – an aircraft landing procedure in which the aircraft is on an even plane with the runway. As the aircraft reduces speed and lift, it drops to the ground in a flat or prone attitude.

Pattern – the flight pattern an aircraft must follow when approaching the airport for landing and when leaving the airport after taking off. Aircraft operating from the airport must follow the same flight pattern in order to reduce the danger of an in-flight collision.

Pitch – the rotation of an airplane about its lateral axis.

Prohibited Area - Airspace designated under FAR Part 73 within which no person may operate an aircraft without the permission of the using agency. It is most always distinctly marked on the VFR sectional maps.

Radial engine – A reciprocating aircraft engine in which all of the cylinders are arranged radially, or spoke-like, around a small crankcase. Also referred to as round engines.

Ramp – the apron or paved surface around a hangar used for parking aircraft.

Resistance - Symbol: R. The opposition to the flow of electrons offered by a device or material. Opposition by resistance causes a loss of power.

Rudder – The movable vertical control surface used to rotate the airplane about its vertical axis. The pilot operates the rudder by the movement of the foot pedals in the cockpit.

See-and-Avoid - The FAA requirement that all pilots are ultimately responsible for separation from other aircraft when visual conditions permit spotting traffic.

Service ceiling – The height above standard sea level beyond which an airplane can no longer climb more than 100 ft./min.

Solo - After typically 12-20 hours of initial flight training, qualified student pilots are permitted to undertake some flights to build experience and confidence without a flight instructor on board. A first solo requires a written endorsement by the student’s flight instructor (and a third-class medical certificate) if training for the private pilot certificate. The first solo is a major event for any pilot and traditionally includes three takeoffs and landings at the student’s home airport.

Stall - An aerodynamic condition that has nothing to do with engine operation. It occurs when lift-producing airflow over the wings is disrupted or lost because the angle of the wings to the airflow (angle of attack) is too high. Student pilots are trained in stall prevention, recognition and recovery.

Student Pilot - A pilot who is training for a sport pilot or private pilot certificate, either before or after the first solo. A sport pilot student pilot must obtain a student pilot certificate through the FAA or a designated source, such as the National Association of Flight Instructors headquarters, while a private pilot student must obtain a third-class medial certificate through a medical examination by an FAA-designated aviation medical examiner before being allowed to fly solo in a powered aircraft. The student pilot certificate, once signed by the flight instructor, becomes the official student pilot certificate and must be carried with the student on every solo flight made.

Tachometer – an instrument that measures the rotating speed of an engine in revolutions per minute (RPM) or in percent of the maximum RPM.

Taxi – To move an airplane on the ground under its own power.

Torque - A twisting, gyroscopic force acting in opposition to an axis of rotation, such as with a turning propeller.

Touch-And-Go - Landing practice wherein an aircraft does not make a full stop after a landing, but proceeds immediately to another take-off. This is a frequent practice when learning takeoffs and landings, provided the runway length is long enough to do so safely.

Uncontrolled spin – A spin in an airplane in which the controls are of little or no use in effecting a recovery.

Undercarriage – A term used to describe an airplane’s entire landing gear.

Useful load – Weight of the occupants, baggage, usable fuel, and drainable oil. The difference between maximum and empty weight.

VFR (Visual Flight Rules) - A defined set of FAA regulations and “rules of the road” covering operation of aircraft primarily by visual reference to the horizon (for aircraft control) and see-and-avoid procedures (for traffic separation). VFR is used by more than 70 percent of all flights; it is not, by definition, uncontrolled or out of control.