Gross weight. The total weight of a fully loaded aircraft including the fuel, oil, crew, passengers, and cargo.
Ground adjustable trim tab. A metal trim tab on a control surface that is not adjustable in flight. Bent in one direction or another
while on the ground to apply trim forces to the control surface.
Ground effect. A condition of improved performance encountered when an airplane is operating very close to the ground. When an
airplane’s wing is under the influence of ground effect, there is a reduction in upwash, downwash, and wingtip vortices. As a result of
the reduced wingtip vortices, induced drag is reduced.
Ground idle. Gas turbine engine speed usually 60-70 percent of the maximum rpm range, used as a minimum thrust setting for ground
operations.
Ground loop. A sharp, uncontrolled change of direction of an airplane on the ground.
Ground power unit (GPU). A type of small gas turbine whose purpose is to provide electrical power, and/or air pressure for starting
aircraft engines. A ground unit is connected to the aircraft when needed. Similar to an aircraft-installed auxiliary power unit.
Ground track. The aircraft’s path over the ground when in flight.
Groundspeed (GS). The actual speed of the airplane over the ground. It is true airspeed adjusted for wind. Groundspeed decreases
with a headwind, and increases with a tailwind.
Gust penetration speed. The speed that gives the greatest margin between the high and low Mach speed buffets.
Gyroscopic precession. An inherent quality of rotating bodies, which causes an applied force to be manifested 90º in the direction of
rotation from the point where the force is applied.
Hand propping. Starting an engine by rotating the propeller by hand.
Heading bug. A marker on the heading indicator that can be rotated to a specific heading for reference purposes, or to command an
autopilot to fly that heading.
Heading indicator. An instrument which senses airplane movement and displays heading based on a 360º azimuth, with the final zero
omitted. The heading indicator, also called a directional gyro, is fundamentally a mechanical instrument designed to facilitate the use
of the magnetic compass. The heading indicator is not affected by the forces that make the magnetic compass difficult to interpret.
Heading. The direction in which the nose of the aircraft is pointing during flight.
Headwind component. The component of atmospheric winds that acts opposite to the aircraft’s flightpath.
High performance aircraft. An aircraft with an engine of more than 200 horsepower.
Horizon. The line of sight boundary between the earth and the sky.
Horsepower. The term, originated by inventor James Watt, means the amount of work a horse could do in one second. One
horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute.
Hot start. In gas turbine engines, a start which occurs with normal engine rotation, but exhaust temperature exceeds prescribed limits.
This is usually caused by an excessively rich mixture in the combustor. The fuel to the engine must be terminated immediately to
prevent engine damage.
Hung start. In gas turbine engines, a condition of normal light off but with rpm remaining at some low value rather than increasing to
the normal idle rpm This is often the result of insufficient power to the engine from the starter. In the event of a hung start, the engine
should be shut down.
Hydraulics. The branch of science that deals with the transmission of power by incompressible fluids under pressure.
Hydroplaning. A condition that exists when landing on a surface with standing water deeper than the tread depth of the tires. When
the brakes are applied, there is a possibility that the brake will lock up and the tire will ride on the surface of the water, much like a
water ski. When the tires are hydroplaning, directional control and braking action are virtually impossible. An effective anti-skid
system can minimize the effects of hydroplaning.
Hypoxia. A lack of sufficient oxygen reaching the body tissues.
Igniter plugs. The electrical device used to provide the spark for starting combustion in a turbine engine. Some igniters resemble
spark plugs, while others, called glow plugs, have a coil of resistance wire that glows red hot when electrical current flows through the
coil.
Impact ice. Ice that forms on the wings and control surfaces or on the carburetor heat valve, the walls of the air scoop, or the
carburetor units during flight. Impact ice collecting on the metering elements of the carburetor may upset fuel metering or stop
carburetor fuel flow.
Inclinometer. An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It
may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and
centrifugal force in a turn.
Indicated airspeed (IAS). The direct instrument reading obtained from the airspeed indicator, uncorrected for variations in
atmospheric density, installation error, or instrument error. Manufacturers use this airspeed as the basis for determining airplane
performance. Takeoff, landing, and stall speeds listed in the AFM or POH are indicated airspeeds and do not normally vary wit h
altitude or temperature.
Indicated altitude. The altitude read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.
Induced drag. That part of total drag which is created by the production of lift. Induced drag increases with a decrease in airspeed.
Induction manifold. The part of the engine that distributes intake air to the cylinders.
Inertia. The opposition which a body offers to a change of motion.
Initial climb. This stag e of th e climb begins when th e airplane leaves the ground and a pitch attitud e has been established to climb
away from the takeoff area.
Instrument Flight Rules (IFR). Rules that govern th e procedur e for conducting fligh t in weather conditions below VFR weather
minimums. The term “IFR” also is used to define weather conditions and the type of flight plan under which an aircraft is operating.
Integral fuel tank. A portion of the aircraft structure, usually a wing, which is sealed off and used as a fuel tank. When a wing is used
as an integral fuel tank, it is called a “wet wing.”
Intercooler. A device used to reduce th e temperature of th e compressed air befor e it enters th e fuel metering device. Th e resulting
cooler air has a higher density, which permits the engine to be operated with a higher power setting.
Internal combustion engine. An engine that produces power as a result of expanding hot gases from the combustion of fuel and air
within the engine itself. A steam engine where coal is burned to heat up water inside the engine is an example of an external
combustion engine.
International Standard Atmosphere (ISA). Standard atmospheric conditions consisting of a temperature of 59 °F (15 °C), and a
barometric pressure of 29.92 "Hg. (1013.2 mb) at sea level. ISA values can be calculated for various altitudes using a stand ard lapse
rate of approximately 2 °C per 1,000 feet.
Interstage turbine temperature (ITT). The temperature of the gases between the high pressure and low pressure turbines.
Inverter. An electrical device that changes DC to AC power.
Irreversible Deceleration and/or Sink Rate. Unrecoverable depletion of mechanical energy as a result of continuous loss of airspeed
and/or altitude coupled with insufficient excess power available under a given flight condition. Failure to recover above a certain
critical AGL altitude results in the airplane hitting the ground regardless of what the pilot does.
Jet-powered airplane. An aircraft powered by a turbojet or turbofan engine.
Kinesthesia. The sensing of movements by feel.
Kinetic energy. Amount of energy due to the airspeed, expressed as ½mV² where m = airplane’s mass and V = airspeed.
Lateral axis. An imaginary line passing through the center of gravity of an airplane and extending across the airplane from wingtip to
wingtip.
Lateral stability (rolling). The stability abou t the longitudinal axis of an aircraf t. Rolling stability or th e ability of an airplan e to
return to level flight due to a disturbance that causes one of the wings to drop.
Lead-acid battery. A commonly used secondary cell having lead as its negative plate and lead peroxide as its positive plate. Sulfuric
acid and water serve as the electrolyte.
Leading edge devices. High lif t devices which are found on th e leading edge of the airfoil. The most common types are fixed slots,
movable slats, and leading edge flaps.
Leading edge flap. A portion of the leading edge of an airplane wing that folds downward to increase the camber, lift, and drag of the
wing. The leading-edge flaps are extended for takeoffs and landings to increase the amount of aerodynamic lift that is produced at any
given airspeed.
Leading edge. The part of an airfoil that meets the airflow first.
Licensed empty weight. The empty weight that consists of th e airframe, engine(s), unusab le fuel, and undrainab le oil plus standard
and optional equipment as specified in the equipment list. Some manufacturers used this term prior to GAMA standardization.
Lift coefficient. A coefficient representing the lift of a given airfoil. Lift coefficient is obtained by dividing th e lift by the free-stream
dynamic pressure and the representative area under consideration.
Lift. One of the four main forces acting on an aircraf t. On a fixed-wing aircraft, an upward force created by th e effect of airflow as it
passes over and under the wing.
Lift/drag ratio (L/D). The efficiency of an airfoil section. It is the ratio of the coefficient of lift to the coefficient of drag for any given
angle of attack.
Lift-off. The act of becoming airborn e as a resu lt of th e wings lifting th e airplane off th e ground, or th e pilot rotating th e nose up,
increasing the angle of attack to start a climb.
Limit load factor. Amount of stress, or load factor, that an aircraft can withstand before structural damage or failure occurs.
Load factor. The ratio of the load supported by the airplane’s wings to the actual weight of the aircraft and its contents. Also referred
to as G-loading.
Longitudinal axis. An imaginary line through an aircraft from nose to tail, passing through its center of gravity. The longitudinal axis
is also called the roll axis of the aircraft. Movement of the ailerons rotates an airplane about its longitudinal axis.
Longitudinal stability (pitching). Stability about the lateral axis. A desirab le characteristic of an airplan e whereby it tends to return
to its trimmed angle of attack after displacement.
Mach buffet. Airflow separation behind a shock-wave pressure barrier caused by airflow over fligh t surfaces exceeding the speed of
sound.
Mach compensating device. A device to alert the pilot of inadvertent excursions beyond its certified maximum operating speed.
Mach critical. The Mach speed at which some portion of th e airflow over th e wing first equals Mach 1.0. This is also th e speed at
which a shock wave first appears on the airplane.
Mach tuck. A condition that can occur when operating a swept-wing airplane in the transonic speed range. A shock wave could form
in the root portion of th e wing and caus e the air behind it to separate. This shock-induced separation caus es the center of pressur e to
move aft. This, combined with th e increasing amoun t of nos e down force at higher speeds to maintain lef t flight, causes the nos e to
“tuck.” If not corrected, the airplane could enter a steep, sometimes unrecoverable dive.
Mach. Speed relative to the speed of sound. Mach 1 is the speed of sound.
Magnetic compass. A device for determining direction measured from magnetic north.
Main gear. The wheels of an aircraft’s landing gear that supports the major part of the aircraft’s weight.
Maneuverability. Ability of an aircraft to change directions along a flightpath and withstand the stresses imposed upon it.
Maneuvering speed (VA). The maximum speed where full, abrupt control movement can be used without overstressing the airframe.
Manifold pressure (MP). The absolu te pressure of th e fuel/ air mixtur e within th e intake manifold, usually indicated in inch es of
mercury.
Maximum allowable takeoff power. The maximum power an engine is allowed to develop for a limited period of time; usually about
one minute.
Maximum landing weight. The greatest weight that an airplane normally is allowed to have at landing.
Maximum ramp weight. The total weight of a loaded aircraf t, including all fuel. It is greater than th e takeoff weight due to the fuel
that will be burned during the taxi and run-up operations. Ramp weight may also be referred to as taxi weight.
Maximum takeoff weight. The maximum allowable weight for takeoff.
Maximum weight. The maximum authorized weight of the aircraft and all of its equipment as specified in th e Type Certificate Data
Sheets (TCDS) for the aircraft.
Maximum zero fuel weight (GAMA). The maximum weight, exclusive of usable fuel.
Minimum controllable airspeed. An airspeed at which any further increase in angle of attack, increase in load factor, or reduction in
power, would result in an immediate stall.
Minimum drag speed (L/D MAX). The point on the total drag curve where the lift-t o-drag ratio is the greatest. At this speed, total
drag is minimized.
Mixture. The ratio of fuel to air entering the engine’s cylinders.
MMO. Maximum operating speed expressed in terms of a decimal of Mach speed.
Moment arm. The distance from a datum to the applied force.
Moment index (or index). A moment divided by a constant such as 100, 1,000, or 10,000. Th e purpose of using a moment index is to
simplify weight and balance computations of airplanes where heavy items and long arms result in large, unmanageable numbers.
Moment. The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (lb-in). Total moment is
the weight of the airplane multiplied by the distance between the datum and the CG.
Movable slat. A movable auxiliary airfo il on th e leading edg e of a wing. I t is closed in norm al flight but extends at high ang les of
attack. This allows air to continue flowing over the top of the wing and delays airflow separation.
Mushing. A flight condition caused by slow speed where the control surfaces are marginally effective.
N1, N 2, N 3. Spool speed expressed in percent rpm. N 1 on a turboprop is the gas producer speed. N 1 on a turbofan or turbojet
engine is the fan speed or low pressure spool speed. N 2 is the high pressure spool speed on engine with 2 spools and medium pressure
spool on engines with 3 spools with N3 being the high pressure spool.
Nacelle. A streamlined enclosure on an aircraft in which an engin e is mounted. On multiengine propeller-driven airplanes, the nacelle
is normally mounted on the leading edge of the wing.
Negative stat ic stability. The in itial tendency of an aircraf t to continu e away from th e origin al s tate of equilibrium after being
disturbed.
Negative torque sensing (NTS). A system in a turboprop engin e that prevents th e engine from being driven by th e propeller. The
NTS increases the blade angle when the propellers try to drive the engine.
Neutral static stability. The initial tendency of an aircraft to remain in a new condition after its equilibrium has been disturbed.
Nickel-cadmium battery (NiCad). A battery mad e up of alkalin e secondary cells. Th e positiv e p lates are nick el hydroxide, the
negative plates are cadmium hydroxide, and potassium hydroxide is used as the electrolyte.
Normal category. An airplane that has a seating configuration, excluding pilo t seats, of nin e or less, a maximum certificated takeoff
weight of 12,500 pounds or less, and intended for nonacrobatic operation.
Normalizing (turbonormalizing). A turbocharger that maintains sea level pressure in the induction manifold at altitude.
Octane. The rating system of aviation gasoline with regard to its antidetonating qualities.
Overboost. A condition in which a reciprocating engine has exceeded the maximum manifold pressure allowed by the manufacturer.
Can cause damage to engine components.
Overspeed. A condition in which an engin e has produced mor e rpm than th e manufacturer recommends, or a condition in which the
actual engine speed is higher than the desired engine speed as set on the propeller control.
Overtemp. A condition in which a device has reached a temperature above that approved by the manufacturer or any exhaust
temperature that exceeds the maximum allowable for a given operating condition or time limit. Can cause internal damage to an
engine.
Overtorque. A condition in which an engine has produced more torque (power) than the manufacturer recommends, or a condition in
a turboprop or turboshaft engine where the engine power has exceeded the maximum allowable for a given operating condition or time
limit. Can cause internal damage to an engine.
Parasite drag. That par t of to tal drag created by th e design or shap e of airplan e parts. Parasit e drag increas es with an increas e in
airspeed.
Payload (GAMA). The weight of occupants, cargo, and baggage.
P-factor. A tendency for an aircraft to yaw to the left due to the descending propeller blade on the right producing more thrust than the
ascending blade on the left. This occurs when the aircraft’s longitudinal axis is in a climbing attitude in relation to the relative wind.
The P-factor would be to the right if the aircraft had a counterclockwise rotating propeller.
Pilot’s Operating Handbook (POH). A document developed by the airplane manufacturer and contains the FAA-approved Airplane
Flight Manual (AFM) information.
Piston engine. A reciprocating engine.
Pitch. The rotation of an airplane about its lateral axis, or on a propeller, the blade angle as measured from plane of rotation.
Pivotal altitude. A specific altitude at which, when an airplan e turns at a given groundspeed, a projecting of th e sighting reference
line to a selected point on the ground will appear to pivot on that point.
Pneumatic system. The power system in an aircraft used for operating such items as landing gear, brakes, and wing flaps with
compressed air as the operating fluid.
Porpoising. Oscillating around the lateral axis of the aircraft during landing.
Position lights. Lights on an aircraft consisting of a red light on the left wing, a green light on the right wing, and a white light on the
tail. CFRs require that these lights be displayed in flight from sunset to sunrise.
Positive static stability. The initial tendency to return to a state of equilibrium when disturbed from that state.
Potential energy. Amount of energy due to the altitude, expressed as mgh, where m = airplane’s mass, and g = gravitational constant,
and h = altitude.
Power available. The airplane’s rate of energy gain due to maximum available engine thrust at a given airspeed. Expressed as TV,
where T = engine thrust, and V = airspeed. Usually measured in horsepower, foot-pound per minute, or foot-pound per second.
Power distribution bus. See bus bar.
Power lever. The cockpit lever connected to the fuel control unit for scheduling fuel flow to the combustion chambers of a turbine
engine.
Power required. The airplane’s rate of energy loss due to total drag at a given airspeed. Expressed as DV, where D = total drag, and V
= airspeed. Usually measured in horsepower, foot-pound per minute, or foot-pound per second.
Power. Implies work rate or units of work per unit of time, and as such, it is a function of the speed at which the force is developed.
The term “power required” is generally associated with reciprocating engines.
Powerplant. A complete engine and propeller combination with accessories.
Practical slip limit. The maximum slip an aircraft is capable of performing due to rudder travel limits.
Precession. The tilting or turning of a gyro in response to deflective forces causing slow drifting and erroneous indications in
gyroscopic instruments.
Preignition. Ignition occurring in the cylinder before the time of normal ignition. Preignition is often caused by a local hot spot in the
combustion chamber igniting the fuel/air mixture.
Pressure altitude. The altitude indicated when the altimeter setting window (barometric scale) is adjusted to 29.92. This is the altitude
above the standard datum plane, which is a theoretical plane where air pressure (corrected to 15 ºC) equals 29.92 "Hg. Pressure
altitude is used to compute density altitude, true altitude, true airspeed, and other performance data.
Profile drag. The total of the skin friction drag and form drag for a two-dimensional airfoil section.
Propeller blade angle. The angle between the propeller chord and the propeller plane of rotation.
Propeller lever. The control on a free power turbine turboprop that controls propeller speed and the selection for propeller feathering.
Propeller slipstream. The volume of air accelerated behind a propeller producing thrust.
Propeller synchronization. A condition in which all of the propellers have their pitch automatically adjusted to maintain a constant
rpm among all of the engines of a multiengine aircraft.
Propeller. A device for propelling an aircraft that, when rotated, produces by its action on the air, a thrust approximately
perpendicular to its plane of rotation. It includes the control components normally supplied by its manufacturer.
Ramp weight. The total weight of the aircraft while on the ramp. It differs from takeoff weight by the weight of the fuel that will be
consumed in taxiing to the point of takeoff.
Rate of turn. The rate in degrees/second of a turn.
Reciprocating engine. An engine that converts the heat energy from burning fuel into the reciprocating movement of the pistons. This
movement is converted into a rotary motion by the connecting rods and crankshaft.
Reduction gear. The gear arrangement in an aircraft engine that allows the engine to turn at a faster speed than the propeller.
Region of reverse command. Flight regime in which flight at a higher airspeed requires a lower power setting and a lower airspeed
requires a higher power setting in order to maintain altitude.
Registration certificate. A State and Federal certificate that documents aircraft ownership.
Relative wind. The direction of the airflow with respect to the wing. If a wing moves forward horizontally, the relative wind moves
backward horizontally. Relative wind is parallel to and opposite the flightpath of the airplane.
Reverse thrust. A condition where jet thrust is directed forward during landing to increase the rate of deceleration.
Reversing propeller. A propeller system with a pitch change mechanism that includes full reversing capability. When the pilot moves
the throttle controls to reverse, the blade angle changes to a pitch angle and produces a reverse thrust, which slows the airplane down
during a landing.
Roll. The motion of the aircraft about the longitudinal axis. It is controlled by the ailerons.
Roundout (flare). A pitch-up during landing approach to reduce rate of descent and forward speed prior to touchdown.
Rudder. The movable primary control surface mounted on the trailing edge of the vertical fin of an airplane. Movement of the rudder
rotates the airplane about its vertical axis.
Ruddervator. A pair of control surfaces on the tail of an aircraft arranged in the form of a V. These surfaces, when moved together by
the control wheel, serve as elevators, and when moved differentially by the rudder pedals, serve as a rudder.
Runway centerline lights. Runway centerline lights are installed on some precision approach runways to facilitate landing under
adverse visibility conditions. They are located along the runway centerline and are spaced at 50-foot intervals. When viewed from the
landing threshold, the runway centerline lights are white until the last 3,000 feet of the runway. The white lights begin to alternate with
red for the next 2,000 feet, and for the last 1,000 feet of the runway, all centerline lights are red.
Runway cente rline markings. The runway centerlin e identif ies th e center of th e runway and provid es alignment guidance during
takeoff and landings. The centerline consists of a line of uniformly spaced stripes and gaps.
Runway edge lights. Runway edge lights are used to outline the edges of runways during periods of darkness or restricted visibility
conditions. These light systems are classified according to the intensity or brightness they are capable of producing: they are the High
Intensity Runway Lights (HIRL), Medium Intensity Runway Lights (MIRL), and the Low Intensity Runway Lights (LIRL). The HIRL
and MIRL systems have variable intensity controls, whereas the LIRLs normally have one intensity setting.
Runway end identifier lights (REIL). One component of the runway lighting system. Th ese lights are installed at many airfields to
provide rapid and positive identification of the approach end of a particular runway.
Runway incursion. Any occurrence at an airport involving an aircraft, vehicle, person, or object on the ground that creates a collision
hazard or results in loss of separation with an aircraft taking off, intending to takeoff, landing, or intending to land.
Runway threshold markings. Runway threshold markings come in two configurations. They either consist of eight longitudinal
stripes of uniform dimensions disposed symmetrically about the runway centerline, or the number of stripes is related to the runway
width. A threshold marking helps identify the beginning of the runway that is available for landing. In some instances, the landing
threshold may be displaced.
Safety (SQUAT) switch. An electrical switch mounted on on e of th e landing gear struts. I t is used to sens e when the weight of the
aircraft is on the wheels.
Scan. A procedure used by the pilot to visually identify all resources of information in flight.
Sea level. A reference height used to determine standard atmospheric conditions and altitude measurements.
Segmented circle. A visual ground based structure to provide traffic pattern information.
Service ceiling. The maximum density altitud e where th e b est rate- of-climb airspeed w ill produce a 100 feet-per-minu te climb at
maximum weight while in a clean configuration with maximum continuous power.
Servo ta b. An auxiliary contro l mounted on a primary contro l surface, which automatically mov es in th e direction oppos ite the
primary control to provide an aerodynamic assist in the movement of the control.
Shaft horse power (SHP). Turboshaft engines are rated in shaf t horsepower and calculated by us e of a dynamometer device. Shaft
horsepower is exhaust thrust converted to a rotating shaft.
Shock waves. A compression wave formed when a body moves through the air at a speed greater than the speed of sound.
Sideslip. A slip in which th e airplane’s longitudinal axis remains par allel to the original flightpath, but the airplane no longer flie s
straight ahead. Instead, the horizontal component of wing lift forces the airplane to move sideways toward the low wing.
Single engine absolute ceiling. The altitude that a twin engine airplane can no longer climb with one engine inoperative.
Single eng ine serv ice ceiling. The altitude that a twin engin e airplane can no longer climb at a r ate greater than 50 fpm with one
engine inoperative.
Skid. A condition where the tail of the airplane follows a path outside the path of the nose during a turn.
Slip. An intentional maneuver to decreas e airspeed or increas e rate of descent, and to compens ate for a crosswind on landing. A sli p
can also be unintentional when the pilot fails to maintain the aircraft in coordinated flight.
Specific excess power (P S). Measured in feet per minute or feet per second, it represents rate of energy change—the ability of an
airplane to climb or accelerate from a given flight condition. Available specific excess power is found by dividing the difference
between power available and power required by the airplane’s weight.