Aviation Glossary: FAA Terms and Acronyms

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1-2-3 rule IFR: A mnemonic for 91.169: from 1 hour before to 1 hour after the ETA, a forecast ceiling of 2,000 feet and visibility of 3 SM exempts a flight from needing an alternate.
100-hour inspection CPL: The inspection 91.409(b) requires of an aircraft carrying persons for hire or used for instruction for hire, within each 100 hours of time in service.
100LLAvgas 100LL PPL: The standard general aviation gasoline: performance number 100, low lead content, dyed blue.
1090ES PPL: Extended squitter: the ADS-B message set carried by a 1090 MHz Mode S transponder with integrated ADS-B.
135-degree point CPL: The checkpoint mirroring the 45-degree point: pitch reaches its maximum descent attitude here, bank about 15 degrees.
300-feet-per-mile rule IFR: A mental check: height above the touchdown zone equals 300 times the distance in nautical miles from the threshold, for a roughly 3-degree glidepath.
3P modelPerceive, Process, Perform IFR: A practical risk-management framework: perceive hazards using PAVE, process what they mean for the flight, then perform the best course of action.
45-degree entry PPL: The recommended pattern entry, intercepting the downwind leg at a 45-degree angle at midfield.
45-degree point CPL: The first checkpoint: pitch reaches its maximum climb attitude here, bank about 15 degrees.
5 PsPlan, Plane, Pilot, Passengers, Programming IFR: An aeronautical decision-making checklist reviewed at several points in a flight to catch a changing risk picture before it becomes an emergency.
500/1,000/2,000Standard cloud clearance PPL: The standard distance from clouds below 10,000 ft MSL: 500 ft below, 1,000 ft above, 2,000 ft horizontal.
7600the lost-communications transponder code IFR: The four-digit code squawked to tell every radar controller watching the target that two-way radio contact has been lost.
7700 PPL: The transponder code for an emergency, set together with the transmission on 121.5 when the situation becomes threatening.
90-degree point CPL: The midpoint of the chandelle where pitch reaches its maximum and bank begins to decrease; the pivot between the maneuver's two halves.
91.213(d) deferral PPL: The part 91 provision allowing a non-required inoperative item to be deactivated or removed and placarded INOPERATIVE rather than repaired before flight.

A

A TOMATO FLAMESDay VFR equipment mnemonic PPL: Memory aid for the equipment required in day VFR flight by 91.205(b).
Aborted start PPL: An immediate shutdown during or after starting because oil pressure, the starter, the brakes, or an abnormal indication requires it.
Absolute altitude PPL: The actual height of the aircraft above the ground directly beneath it (AGL).
Absolute ceiling CPL: The density altitude at which the rate of climb has fallen to zero and only one airspeed sustains level flight; Vx and Vy converge there.
Accelerated stall PPL: A stall occurring above the normal unaccelerated stall speed because load factor, not low airspeed, drove the wing past critical AOA.
Accelerometer PPL: An instrument that measures load factor directly; uncommon on training airplanes, which is why pilots learn to judge Gs from seat pressure.
ACS code CPL: A unique identifier for an element, made of the certificate, the Area of Operation, the task, the element type, and its number.
ADCair data computer PPL: A solid-state computer that calculates airspeed, altitude, and vertical speed from pitot and static pressure, replacing mechanical pitot-static linkages.
Adiabatic process IFR: A temperature change caused by expansion or compression alone, with no heat added or removed - what happens to every rising or descending parcel.
ADMAeronautical Decision-Making PPL: A systematic approach to the mental process pilots use to consistently choose the best course of action given available information.
ADS-BAutomatic Dependent Surveillance-Broadcast PPL: Surveillance in which the aircraft broadcasts its GPS-derived position once a second to ground stations and other aircraft, on 978 or 1090 MHz.
Advection fog PPL: Fog that forms when warm, moist air moves horizontally over a colder surface; needs some wind to form, but lifts into stratus above about 15 knots.
Adverse yaw PPL: A yaw opposite the direction of roll, caused by the extra induced drag of the down-going aileron.
Aerial work CPL: Compensated activity that does not consist of carrying a customer from one point to another: spraying, patrol, photography, jump operations.
After-landing checklist PPL: The AFM/POH list of configuration changes made once the airplane is stopped clear of the runway.
Agonic line PPL: The isogonic line of zero variation, where true north and magnetic north coincide; it passes near Chicago.
AHRSattitude and heading reference system PPL: A solid-state sensor package that replaces mechanical gyros for attitude and heading on electronic flight displays.
Aiming point PPL: The spot on the runway a constant-angle glide path would strike without a round out; it appears stationary in the windscreen while everything else moves.
Air carrier certificate CPL: A certificate issued to a company, distinct from a pilot certificate, required by Part 119 to conduct common carriage.
Air mass PPL: A large body of air that has taken on the temperature and moisture characteristics of the surface region it formed over.
Air Route Traffic Control CenterARTCC (Center) IFR: The facility responsible for separating IFR traffic in the en route structure, organized into sectors and, often, high and low altitude layers.
Aircraft approach categoryapproach category IFR: A grouping (A through E) based on reference landing speed or actual circling speed flown, that determines which line of minimums an aircraft must use.
Airman Knowledge Test Report CPL: The document issued after the test, showing the score and the reference standard codes tied to the missed questions.
Airman Knowledge Testing SupplementFigures supplement CPL: A booklet of illustrations supplied on test day: charts, performance tables, diagrams, referenced by many test questions. The FAA is progressively moving these illustrations into the questions themselves, exam by exam.
AIRMETAirmen's Meteorological Information PPL: An advisory covering weather hazards significant to lighter aircraft, issued every 6 hours as Sierra (IFR/mountain obscuration), Tango (turbulence/wind), or Zulu (icing).
Airworthiness directiveAD PPL: A mandatory FAA order correcting an unsafe condition on a type of aircraft.
Airworthy PPL: Conformance of the aircraft to its type certificate and safe condition for flight, checked by the pilot in command under 91.7.
Alternate airport IFR: An airport listed on an IFR flight plan to which the flight can divert if landing at the destination becomes impossible.
Alternate static source PPL: A backup static pressure port, usually inside the cabin, selected if the primary static port becomes blocked.
Alternator PPL: The engine-driven generator that supplies electrical current in flight and keeps the battery charged.
Ammeter PPL: A zero-centered gauge showing whether the battery is charging or discharging.
ANDSAccelerate North, Decelerate South IFR: A memory aid for the magnetic compass acceleration error seen on easterly and westerly headings.
Angle of attackAOA PPL: The acute angle between the wing's chord line and the relative wind.
Angle of attack indicatorAOA indicator PPL: An instrument that measures the current AOA directly and displays its proximity to the critical AOA.
Anti-collision light systembeacon / strobes CPL: Rotating beacon and/or strobe lights required for night VFR by 14 CFR 91.205(c); may be turned off by the PIC under 91.209(b) if safety requires it.
Antiservo tab PPL: A tab on a stabilator that moves in the same direction as its trailing edge, reducing sensitivity and acting as trim.
Approach gate IFR: An imaginary point 1 NM from the final approach fix, on the side away from the airport and no closer than 5 NM from the threshold, used as the normal minimum vectoring point onto the final approach course.
Approach light systemALS IFR: A lighting system extending out from the runway threshold, one of the ten visual references sufficient on its own under 91.175; ALSF-2 is a specific configuration with sequenced flashing lights.
Approach with vertical guidanceAPV IFR: An instrument approach providing course and glidepath guidance that does not meet the ICAO Annex 10 precision standard, such as LPV or LNAV/VNAV.
Approved course CPL: A training program approved by the FAA at a Part 141 school, whose minimum content is set in that part's appendices.
Area of Operation CPL: A major subdivision of the standard, numbered with Roman numerals and ordered to match the chronological flow of a flight.
Arm PPL: The horizontal distance from the datum to an item's center of gravity; positive aft, negative forward of the datum.
ARROWRequired aircraft documents PPL: Airworthiness certificate, Registration, Radio station license, Operating limitations, Weight and balance data.
ASOS/AWOSAutomated Surface/Weather Observing System IFR: Automated sensor systems that broadcast current surface weather by voice and printed report, without a human observer.
ASRSAviation Safety Reporting System PPL: A voluntary incident reporting system offering limited immunity from enforcement action in exchange for the report.
ATCRBSAir Traffic Control Radar Beacon System PPL: Secondary surveillance radar: an interrogator, the aircraft transponder and a radarscope, reinforcing and identifying targets.
ATISAutomatic Terminal Information Service PPL: A looped recording of weather and airport information, identified by a phonetic letter.
Atmospheric stability IFR: The atmosphere's ability to resist vertical motion; stable air damps small vertical disturbances, unstable air lets them grow.
Attitude indicator PPL: A gyroscopic instrument, typically vacuum driven, displaying pitch and bank attitude.
Attitude instrument flying PPL: Controlling pitch, bank, power and trim by reference to the instruments rather than the outside horizon.
Autokinesis PPL: The illusion that a stationary light is moving, caused by staring at it for more than about 8 to 10 seconds in the dark.
Automatic direction finderADF IFR: The airborne receiver whose needle points continuously toward the tuned NDB station.
Autorotation PPL: The self-sustaining rotation of a spin, produced by different lift and drag on each wing once one is stalled and yawed.
Available landing distance CPL: The distance from the threshold to the hold-short point on a LAHSO runway, published and shorter than the full runway length.
AVEFAssigned, Vector, Expected, Filed IFR: The priority order for choosing a route after a two-way radio failure.
AWOSAutomated Weather Observing System PPL: An automated weather broadcast, printed on the chart in place of a tower or ATIS frequency at many non-towered fields.

B

Back courseBack course approach IFR: An approach flown on the reverse side of a localizer beam, toward the opposite runway, with no usable vertical guidance and a risk of reverse-sensing needle indications.
Ballistic parachute PPL: A rocket-deployed canopy that lowers the whole airplane; deployment destroys the airframe and is intended to save the occupants.
Baro-aiding PPL: A method of substituting a current altimeter setting for one satellite in RAIM calculations.
Base key position CPL: A convenient point in the air on base leg, high enough and close enough to glide to the runway; not a fixed landmark.
Basic empty weight PPL: Standard empty weight plus any optional or special equipment installed, including unusable fuel and full oil.
Basic radar service PPL: Safety alerts, traffic advisories, limited vectoring when requested and sequencing where established, provided to VFR aircraft in contact and in coverage.
BasicMed PPL: An alternative to the medical certificate for certain general-aviation operations, with limits on aircraft and altitude.
Before-takeoff check PPL: The systematic AFM/POH procedure for checking engine, controls, systems, instruments and avionics before flight, done at a run-up position near the runway.
Best angle-of-climb speedVx CPL: The speed that gains the most altitude over the shortest horizontal distance; it increases in indicated airspeed as density altitude rises.
Best glide speedBest glide speed (Vg) PPL: The airspeed giving the greatest glide distance per unit of altitude lost, engine out.
Best rate-of-climb speedVy CPL: The speed that gains the most altitude per unit of time; it decreases in indicated airspeed as density altitude rises, meeting Vx at the absolute ceiling.
Black hole approach PPL: An illusion during approach to an isolated runway with no intermediate lighting, which pushes the pilot to fly too low.
Black-hole approachfeatureless terrain illusion CPL: An illusion on approach to an isolated runway with no surrounding lights, making the aircraft feel higher than it actually is and producing a dangerously low approach.
Blackout landing CPL: A landing practiced or flown with flight-deck lights off or a landing light unusable, judged on the runway lights' perspective alone.
Blade twist PPL: The change in a propeller blade's angle of incidence from a high value at the hub to a low value at the tip, which keeps angle of attack efficient along the whole blade.
Block altitudealtitude window IFR: A crossing restriction given as two stacked values: at or below the top value, at or above the bottom value.
Boost pumpAuxiliary fuel pump PPL: An electrically driven backup fuel pump used for starting and in case the engine-driven pump fails.
Bus bar PPL: A common electrical distribution point connecting the aircraft's power source to the equipment that uses it.

C

Cabin altitude CPL: The altitude, in terms of standard atmospheric pressure, that corresponds to the actual pressure inside a pressurized cabin; the only figure that matters physiologically.
Cabin heater PPL: A system that warms cabin air by circulating it around the exhaust, and the usual entry route for CO into the cabin of a light airplane.
Calendar month PPL: A regulatory deadline unit: validity runs through the last day of the month in which it is due.
Calibrated airspeed (CAS) PPL: Indicated airspeed corrected for instrument and position error.
Camber PPL: The curvature of an airfoil's mean camber line; more camber increases the coefficient of lift at a given AOA, at the cost of more drag.
Carbon dioxideCO2 PPL: The gas whose blood concentration regulates breathing rate; excessive elimination of it, not a lack of oxygen, causes hyperventilation.
Carbon monoxideCO PPL: A colorless, odorless gas produced by every internal combustion engine, from incomplete combustion.
Carburetor heat PPL: A system that routes unfiltered, exhaust-warmed air into the induction system to prevent or melt carburetor ice.
Carburetor icingCarburetor ice PPL: Ice forming inside the carburetor from the temperature drop caused by the venturi's pressure loss and fuel vaporization.
CDICourse Deviation Indicator PPL: The needle showing the aircraft's position relative to the radial selected on the OBS.
Ceiling PPL: The height above the ground of the lowest broken or overcast cloud layer, or the vertical visibility into an obscuration.
Center of gravityCG PPL: The point at which the airplane would balance if suspended there; total moment divided by total weight.
Chandelle CPL: A maximum performance 180-degree climbing turn, flown in two 90-degree halves, ending wings-level just above stall speed.
Changeover pointCOP IFR: The point along an airway where a pilot switches navigation reference from the station behind to the station ahead; near the midpoint unless otherwise charted.
Chart Supplement PPL: The FAA publication listing detailed airport data - hours, services, remarks - that a sectional chart does not have room to print.
Charted visual flight procedureCVFP IFR: A visual approach published with defined fixes, altitudes, and ground track, often built for noise, terrain, or traffic reasons, still not an instrument approach procedure.
Chemical CO detectorSpot detector PPL: A low-cost chemical detector that changes color in the presence of carbon monoxide and has a limited, dated service life.
Chord line PPL: A straight reference line from an airfoil's leading edge to its trailing edge, used to measure angle of attack.
CHTcylinder head temperature PPL: A direct, immediate reading of cylinder metal temperature, used to detect overheating before it causes damage.
Circling approach areacircling protected area IFR: The obstacle clearance area around an airport within which a circling maneuver is protected, sized by approach category and, under current design criteria, by height above airport (HAA).
Circling Minimums Decision AltitudeCMDA IFR: The MDA published for a circling approach, below which the aircraft may not descend until positioned for a normal descent and landing on the intended runway.
Circuit breaker PPL: A resettable device that opens a circuit under an overload, protecting the circuit and equipment from damage.
Civil twilight PPL: The period bracketing sunrise and sunset used to define loggable night flight time.
Class B airspace PPL: Controlled airspace, individually shaped, around the nation's busiest airports, requiring a specific ATC clearance to enter.
Class C airspace PPL: Radar-serviced airspace with a 5 NM core and a 10 NM outer ring up to 4,000 ft above the airport. Two-way radio contact must be established.
Class D airspace PPL: Airspace around a towered airport, up to 2,500 ft above the airport. Two-way radio contact must be established.
Class G airspace PPL: Uncontrolled airspace, extending from the surface to the base of the overlying Class E.
Clear ice PPL: Glossy, dense, transparent ice formed from larger supercooled droplets or freezing rain, typically in warmer sub-freezing temperature bands; the hardest to see and most airfoil-distorting type.
Clearance limit IFR: The point to which a clearance authorizes flight, most often the destination airport.
Clearance void time IFR: The time by which an aircraft must be airborne, after which an unused clearance becomes void and reserved airspace is released.
Clearing the engine CPL: Briefly advancing the throttle during a prolonged idle descent to prevent spark plug fouling and excessive cooling.
Climb gradientft/NM IFR: A required rate of climb expressed as feet gained per nautical mile of ground track, convertible to feet per minute using groundspeed.
CLMAX PPL: The peak value of the coefficient of lift for a given airfoil, reached at the critical angle of attack.
Coefficient of liftCL PPL: A dimensionless number representing how much lift an airfoil produces at a given AOA, for a given dynamic pressure.
Cold front PPL: The boundary where advancing cold air pushes under and lifts retreating warmer air, producing a narrow, often violent band of weather.
Common carriage CPL: An offer made to the public to transport persons or property from one point to another for compensation; all four elements must be present together.
Common purpose PPL: An FAA test: the pilot must have an independent reason for making the trip to the destination.
Compass locator IFR: A low-power NDB collocated with an ILS outer or middle marker, identified by the first two (outer) or last two (middle) letters of the localizer identifier.
Compass rose PPL: A set of lines painted on a ramp or taxiway at 30-degree intervals, oriented to magnetic north, used to swing the compass.
Complex airplane CPL: An airplane with retractable landing gear, flaps, and a controllable-pitch propeller, all three at once; for a seaplane, flaps and a controllable-pitch propeller alone are enough.
Compulsory reporting point IFR: A charted fix, shown as a solid triangle, over which a position report is required on every IFR flight using that route, regardless of altitude.
Cone of confusion IFR: The volume of airspace directly above a VOR station where CDI indications become erratic before the TO/FROM flag flips.
Cones PPL: Retinal receptors concentrated at the center of the retina, responsible for daylight vision, fine detail, and color.
Confirmation bias CPL: Weighing new information by whether it agrees with a decision already made, so that deteriorating reports are read as holding steady.
Constant radius CPL: The goal of the maneuver: holding the same distance from the reference point despite groundspeed changing with heading relative to the wind.
Constant-speed propeller PPL: A controllable-pitch propeller whose governor automatically adjusts blade angle to hold a selected rpm constant.
CONTACT PPL: The hand-propping command meaning the magnetos are ON, chosen because it cannot be confused with SWITCH OFF.
Contact approachcontact approach clearance IFR: A pilot-requested-only authorization to deviate from the published instrument approach and proceed to the airport by visual reference to the surface, remaining clear of clouds with at least 1 SM flight visibility.
Continuous descent final approachCDFA IFR: A technique flying a steady rate of descent from the FAF to the MDA, arriving there near the point the runway should become visible, instead of leveling off early.
Control effectiveness PPL: The response produced by a given control movement; it falls with airspeed because less air flows over the surfaces.
Convective currents CPL: Local updrafts and downdrafts produced by uneven surface heating; they build through the day and are strongest by midafternoon.
Convective OutlookAC PPL: The Storm Prediction Center's forecast of severe thunderstorm potential in five categories, defined by tornado, 50-knot gust or one-inch hail thresholds.
Convective SIGMETConvective Significant Meteorological Information PPL: An FAA weather advisory issued for severe thunderstorm criteria (50-knot surface winds, three-quarter-inch hail, or a tornado) or for widespread thunderstorm coverage; issued at 55 past the hour, valid 2 hours.
Coriolis illusion CPL: A false sensation of turning or accelerating on a different axis, caused by head movement during a sustained turn.
Corkscrewing slipstreamSpiraling slipstream CPL: The spiral rotation the propeller imparts to the slipstream, which strikes the vertical fin and yaws the nose left, and also produces a rolling moment.
Course sensitivity IFR: The angular or linear deviation that produces full-scale deflection on the course deviation indicator - about 10-12 degrees for a VOR, 2.5 degrees for a localizer.
Cowl flaps PPL: Hinged panels that control the airflow exiting the engine cowling, opened to increase cooling and closed to retain heat.
Crab method PPL: A crosswind technique that holds a wings-level heading into the wind and removes the crab with rudder the instant before touchdown.
CRAFT IFR: A clearance-copying technique for the fixed order of a departure clearance: Clearance limit, Route, Altitude, Frequency, Transponder.
Crankcase breather PPL: A vent that relieves crankcase pressure and through which excess oil is expelled overboard.
Critical angle of attack PPL: The angle of attack, fixed for a given airfoil (typically 16 to 20 degrees), at which CLMAX is reached and lift begins to drop off sharply.
Cross-checkSCAN PPL: The trained habit of moving attention between instruments so that no single one is believed on its own.
Cross-control stall PPL: A stall entered in uncoordinated flight, with aileron and rudder applied in opposite directions -- classically during an overshot base-to-final turn.
Cross-country flight CPL: A flight that includes a landing at a point other than the point of departure; the minimum distances required vary by certificate.
Crosswind component PPL: The part of the wind acting perpendicular to the course or runway, equal to wind speed multiplied by the sine of the angle off the nose.
Cruise clearance IFR: A clearance authorizing any altitude from the minimum IFR altitude up to a stated ceiling, with climbs and descents within that block at pilot discretion.
CTAFCommon Traffic Advisory Frequency PPL: The self-announce frequency used at a non-towered airport, or at a towered airport when the tower is closed.
Cumulative hour PPL: Total transmitter run time, added across activations, which is what triggers ELT battery replacement rather than a calendar date.
CWACenter Weather Advisory IFR: A short-fused, roughly 2-hour nowcast issued by an ARTCC, supplementing an existing advisory or flagging conditions approaching advisory criteria.
Cyanosis PPL: A blue discoloration of the fingernails and lips caused by desaturated (oxygen-poor) blood.
Cylinder head temperatureCHT PPL: The temperature of a cylinder head, a direct and immediate indicator of engine thermal load.

D

Dark adaptation CPL: The roughly 30-minute process by which the eye reaches maximum night sensitivity; destroyed within about a second by a bright light.
Data link service providerDLSP IFR: The commercial supplier of weather and other data to an EFB, whose disclaimer and product limitations the pilot is expected to know.
DatumReference datum PPL: The imaginary vertical plane, fixed by the manufacturer, from which every arm and the CG range are measured.
Dead reckoning PPL: Navigation by computation from a known position, using heading, true airspeed, wind, and elapsed time.
DECIDE modelDetect, Estimate, Choose, Identify, Do, Evaluate PPL: A six-step, continuous-loop decision process for responding to a change that has already occurred in flight.
Decision altitudeDA IFR: The altitude on a precision or APV approach at which the missed approach must begin if the required visual references are not in sight; a small overshoot during the missed approach is expected and accounted for.
Decision altitude / decision heightDA/DH IFR: A decision point on an approach with vertical guidance, at which a brief continued descent during the transition to a climb is accounted for in the procedure design.
Decision point CPL: A specific, predetermined location, time, or value at which a pilot commits to continuing a flight or abandoning the plan.
Decompression sicknessDCS PPL: Nitrogen coming out of solution as bubbles when pressure falls; the bends are joint pain, and scuba diving before flight loads the body with the nitrogen that causes it.
Decompression sickness after diving CPL: Nitrogen absorbed during a scuba dive coming out of solution as bubbles at altitude; prevented by waiting 12 or 24 hours depending on the dive and the flight altitude.
Dehydration PPL: A critical loss of body water; first sign is fatigue, and thirst arrives only at about a 1.5 quart deficit.
Deicing boots CPL: Inflatable rubber leading-edge covers that crack accumulated ice by pneumatic inflation, cycled from the flight deck.
Demonstrated crosswind component CPL: The 90-degree crosswind, at least 0.2 times the power-off stall speed, in which the airplane was shown controllable during certification; published in the AFM or POH.
Density altitude PPL: Pressure altitude corrected for non-standard temperature; the altitude in the standard atmosphere at which the airplane's actual performance would be found.
Departure End of RunwayDER IFR: The end of the runway available for the ground run of a departing aircraft; the reference point climb gradients and obstacle distances are measured from.
Descend viadescend via clearance IFR: An ATC clearance instructing the pilot to follow the lateral path and altitudes published on a STAR without individual altitude clearances at each fix.
Design maneuvering speedVA PPL: The speed below which a single full control deflection, on a single axis, in smooth air, will not damage the airplane. Falls with decreasing weight.
Detonation PPL: An uncontrolled, explosive ignition of the fuel-air mixture that produces destructive pressure spikes in the cylinder.
Developed phase PPL: The spin in equilibrium: rotation rate, airspeed and vertical speed stabilized on a nearly vertical flightpath.
Deviation PPL: A compass error specific to one aircraft, caused by its own magnetic fields and wiring, and recorded on a correction card for each heading.
Dew point PPL: The temperature to which air must cool, at constant pressure, to become saturated with water vapor.
Differential braking PPL: Independent left and right brakes that supplement nosewheel or tailwheel steering on the ground.
Differential pressurepsid CPL: The difference between cabin pressure and outside atmospheric pressure, limited by the structural certification of the fuselage.
Dihedral PPL: The upward angle of the wings from horizontal, which produces a restoring roll when a sideslip develops.
Direct entrydirect entry procedure IFR: A holding entry flown when the arrival heading lets the aircraft fly straight to the fix and turn immediately to follow the pattern.
Direction finding assistanceDF PPL: A service in which the controller plots the aircraft from timed transmissions and then vectors it to a suitable landing site.
Direction finding steerDF CPL: A bearing to the aircraft taken from its own transmissions by a ground facility, used to plot its position and give vectors when radar cannot.
Disqualifying medical condition CPL: A condition listed in the regulations whose presence bars issuance or use of a medical certificate absent an FAA decision.
Ditching CPL: A forced landing on water, a specific risk of night flight over large bodies of water in a single-engine airplane.
Diversion PPL: Abandoning the planned destination for an alternate, for weather, a malfunction, or a plan that no longer works.
DMEDistance Measuring Equipment PPL: A UHF navigation aid, paired with a VOR or VORTAC, that reads slant-range distance to the station in nautical miles.
DME arcdistance arc IFR: An approach segment flown at a constant distance from a VOR or VORTAC, curving the aircraft from its arrival direction onto the intermediate or final approach course.
Downlock CPL: A mechanical device that holds the gear leg in the extended position independent of hydraulic or electrical pressure.
Downwind key position CPL: The point abeam the landing spot on the downwind leg where the throttle is closed to begin a power-off approach.
Downwind leg PPL: The pattern leg parallel to the runway, opposite the landing direction, flown at traffic pattern altitude.
Drag PPL: The rearward force resisting an airplane's motion through the air, opposing thrust.
Drift angle PPL: The angle between the aircraft's heading and its actual track over the ground when no wind correction has been applied.
Dual ignition PPL: Two separate magnetos, each firing one of two spark plugs per cylinder, for redundancy and faster combustion.
Dual-purpose fixIAF/IF fix IFR: A single charted fix that serves as an IAF when a course reversal is being flown from it, and as an IF once the aircraft is established inbound past it.
Dutch roll PPL: A coupled rolling and yawing oscillation caused by strong dihedral relative to directional stability.
Dynamic stability PPL: How an airplane's disturbed motion evolves over time: damped (shrinking), neutral, or divergent (growing) oscillations.

E

E6BFlight computer PPL: A circular slide rule built for aeronautical calculations, with a calculation side and a wind side; also available as an electronic calculator.
Ear block PPL: Pain and reduced hearing when the middle ear cannot equalize through the Eustachian tube, worst on descent when the partial vacuum constricts the tube.
EFCExpect Further Clearance IFR: A time, given by ATC before contact is lost, at which the pilot should expect a new clearance if nothing else has been heard.
EGTExhaust Gas Temperature PPL: The temperature of the exhaust gases, used as the primary reference for setting the mixture.
Electrohydraulic system CPL: A hydraulic gear retraction system whose pump is powered electrically rather than by the engine.
Electronic flight bagEFB IFR: A device displaying charts, documents and often weather in place of paper; the pilot remains responsible for its proper use.
Elevator trim stall PPL: A stall produced when full go-around power is applied with the trim set nose-up for the approach and the pilot does not hold the nose down.
ELTEmergency Locator Transmitter PPL: Distress beacon required by 91.207, inspected every 12 calendar months.
Embedded thunderstorm IFR: A cumulonimbus cell hidden inside a broader stratiform cloud layer, invisible to a pilot inside the layer.
Emergency AutolandEAL PPL: A system that stabilizes the airplane, checks for pilot responsiveness, and if there is none, descends, selects an airport and lands, broadcasting its intentions.
Emergency gear extension CPL: An alternate means of lowering the gear — free-fall release, compressed gas, or a manual hand crank — used when the normal system fails; generally not reversible in flight.
Emergency locator transmitterELT PPL: A self-contained radio transmitter that transmits automatically on the impact of a crash, required by 14 CFR 91.207.
Empty-field myopia PPL: A relaxed, short focal distance the eye settles into when there is nothing specific to focus on outside the aircraft, such as above a cloud layer.
Endorsement PPL: A signed entry by an instructor in a pilot's logbook, certifying a skill or authorizing an operation.
Endorsement (61.31) PPL: A logbook authorization to fly a complex, high-performance, tailwheel, or pressurized aircraft.
Erection mechanism PPL: The gravity-driven system inside an attitude indicator that brings the gyro to a vertical spin axis after startup, and that also produces its acceleration and deceleration errors.
Essential bus PPL: A priority electrical bus that keeps critical instruments and radios powered from the battery if normal electrical generation is lost.
Expect further clearanceEFC IFR: The time by which a pilot holding can expect to receive further clearance from ATC; used to plan fuel and, if communications are lost, to determine when to leave the hold.
Expectation bias CPL: Hearing or seeing what one expected rather than what was said or shown; in taxi, reading back the runway you always use instead of the one assigned.
Explosive decompression CPL: A cabin pressure loss faster than the lungs can decompress on their own, generally under about 0.5 seconds.

F

FADECFull Authority Digital Engine Control CPL: A digital computer and associated accessories that manage engine and propeller together; included in the complex airplane definition even without a separate propeller lever.
False glideslopeFalse glideslope course IFR: A steeper, spurious glidepath radiated by the glideslope antenna above the real path, near 9-12 degrees, avoided by intercepting the real glidepath from below.
FDC NOTAMFlight Data Center NOTAM PPL: A NOTAM issued by the National Flight Data Center carrying regulatory information such as chart changes, interim IFR procedures, and temporary flight restrictions.
Feathering CPL: Rotating propeller blades edge-on to the relative wind to minimize drag on a stopped engine; standard on many multiengine airplanes, not present on most single-engine installations.
Final approach fixFAF IFR: The point, marked by a Maltese cross on a non-precision approach, where the final descent segment begins.
FIS-BFlight Information Service-Broadcast PPL: The ground-to-air data link over 978 MHz UAT that delivers weather and aeronautical information to the flight deck, for information only.
Five dosing intervals PPL: The handbook's rule of thumb for waiting after a medication with adverse side effects: five times the dosing interval, so 30 hours for a 6-hour drug.
Fixed-pitch propeller PPL: A propeller whose blade angle is set by the manufacturer and cannot be adjusted; available as a climb or cruise design.
FLAPSNight VFR equipment mnemonic PPL: Memory aid for the additional equipment required at night by 91.205(c).
Flight followingVFR radar traffic advisory service PPL: Radar traffic advisories provided to VFR flights on request, workload permitting.
Flight log CPL: The planning form carrying course, heading, groundspeed, distance, time and fuel for each leg, on which actual times are written and compared with the plan.
Flight reviewSometimes called BFR (biennial flight review) PPL: The recurrent check required by 61.56: one hour of ground training and one hour of flight training within 24 calendar months.
Flight Service StationFSS IFR: A facility providing pilot briefings, flight plan filing and relay, NOTAM origination, and weather broadcasts -- usually a pilot's first ATC contact.
Flight visibility PPL: The average distance at which unlighted objects can be identified by day from the cockpit.
Flow and check CPL: A checklist method in which the flight deck is configured from memory in a fixed pattern, then the checklist is read to confirm nothing was missed.
Forced landing PPL: An immediate landing, on or off an airport, made necessary by an inability to continue flight, flown at the slowest airspeed compatible with control.
Forward slip PPL: An intentional slip that keeps the airplane on its original flightpath with the nose yawed away from it, used to lose altitude without gaining airspeed.
Fowler flap PPL: A slotted flap that slides aft on tracks, increasing wing area and camber with little drag before it deflects.
Freezing level IFR: The altitude at which air temperature reaches 0C; can occur twice when an inversion creates a warm layer between two colder ones.
FSSFlight Service Station IFR: The primary source of preflight and inflight weather briefings, reachable 24 hours a day at 1-800-WX-BRIEF.
Fuel flowage limitation PPL: An AFM/POH restriction on slip duration or fuel quantity, intended to prevent fuel starvation when fuel is forced to one side of a tank.
Fuel reserve PPL: 30 minutes of flight at cruise speed by day, 45 minutes by night, counted after the first point of intended landing.
Fuel starvation CPL: Fuel aboard that is not reaching the engine, from a dry tank on the selector, a blocked vent, a mispositioned selector or a failed pump; often restored by switching tanks.
Fuel sump check PPL: Draining fuel at the low points of the system to check for water, sediment, and the wrong fuel type.
Fuel vent PPL: A passage that keeps a fuel tank at atmospheric pressure as fuel is drawn out; if blocked, fuel flow can stop even with fuel remaining.
Full stall PPL: The critical angle exceeded: an uncommanded nose-down pitch that cannot be readily arrested, possibly with an uncommanded roll.

G

Get-there-itis PPL: A fixation on reaching the original destination that overrides consideration of any safer alternative.
GlidepathGP IFR: A computed vertical guidance path from WAAS or barometric VNAV, printed as an angle over a threshold crossing height, distinct from a true ILS glideslope (GS).
GlideslopeGS IFR: The UHF component of the ILS providing vertical guidance, normally near a 3-degree path, automatically paired to the localizer frequency.
GNSS MEAG-suffix MEA IFR: A minimum en route altitude built assuming GPS/RNAV navigation rather than VOR signal reception, printed with a trailing G.
Governor PPL: The device that senses engine rpm and adjusts propeller blade angle to hold the pilot-selected rpm constant.
GRABCARD IFR: A memory aid for the equipment 91.205(d) and (e) add for IFR flight: generator, radios, attitude indicator, ball, clock, altimeter, rate of turn indicator, DME.
Graphical Forecasts for AviationGFA PPL: The interactive tool that replaced the textual Area Forecast outside Alaska, spanning 18 hours back and 18 hours forward with switchable layers.
Graveyard spiral PPL: A descending turn the pilot does not perceive as a turn, sustained by a false or missing attitude reference and the vestibular illusion of level flight.
Gravity-feed system PPL: A fuel system, typical of high-wing airplanes, in which the tanks sit above the engine and fuel flows to it by gravity alone.
Green arc CPL: The tachometer range marking normal continuous engine operation; sustained rpm below it usually means the propeller is windmilling and driving the engine.
Ground Communication OutletGCO IFR: An unstaffed ground-to-ground facility that lets a pilot reach ATC or FSS by radio through a telephone connection, used to get a clearance or close a flight plan.
Ground effect PPL: A change in a wing's aerodynamics caused by the surface restricting airflow, reducing induced drag and increasing CL at a constant AOA, most noticeable within about one wingspan of the ground.
Ground fog halohalo/glow CPL: A glow appearing around ground lights at night, an early and reliable sign of ground fog forming.
Ground loop PPL: An uncontrolled swerve on the ground in which the aft center of gravity of a tailwheel airplane tries to get ahead of the main wheels.
Ground power unitGPU PPL: External electrical power connected through an aircraft receptacle to provide energy for starting, especially useful in cold weather.
Ground reference maneuver PPL: A maneuver flown to a track over the ground rather than a heading through the air, generally between 600 and 1,000 feet AGL.
Ground roll PPL: The distance the airplane travels along the runway surface before lifting off; the first performance number that stretches as density altitude rises.
Ground visibility PPL: Visibility observed from the airport, required at 3 SM to take off or land within surface-designated airspace.
Groundspeed PPL: Speed over the earth; with bank angle, it determines the radius of a turn relative to the ground.
Guard PPL: 121.5 MHz, the emergency frequency monitored by most facilities and many airliners.
Gust factor PPL: The difference between the gust and steady wind speeds; the AFH adds at most one half of it to the approach speed in gusty air.
Gust front PPL: The leading edge of rain-cooled downdraft air spreading out ahead of a thunderstorm, capable of reaching 15 miles ahead of the storm's precipitation.
Gust lock PPL: A device securing the flight controls on the ground so wind cannot slam them against their stops.
Gyroscopic precession PPL: A spinning propeller's tendency to respond to an applied force 90 degrees later, in the direction of rotation.

H

HAAHeight Above Airport IFR: A circling minimum expressed as height above the airport elevation, published alongside the MSL circling altitude, and one of the factors that sizes the modern circling protected area.
Hand propping PPL: Starting an engine by pulling the propeller through by hand; a two-person procedure with serious to fatal hazards, reserved for airplanes built without an electric starter.
HATHeight Above Touchdown IFR: The MDA or DA expressed as a height above the TDZE rather than as an MSL altitude; published alongside the MSL minimum on the chart.
Hazardous attitudes PPL: Five recurring thought patterns identified as interfering with sound pilot judgment, each paired with a specific antidote.
Heading indicator PPL: A directional gyroscope, typically vacuum driven, displaying heading and periodically reset against the magnetic compass.
Height above touchdownHAT IFR: The published minimum altitude expressed as height above the touchdown zone elevation, rather than above sea level.
Hemispheric rule PPL: The 14 CFR 91.159 requirement that VFR cruising altitudes above 3,000 ft AGL follow odd-thousand-plus-500 for magnetic courses 0-179 degrees and even-thousand-plus-500 for 180-359 degrees.
Hemoglobin PPL: The blood molecule that transports oxygen; carbon monoxide binds to it roughly 200 times more readily than oxygen does.
High-performance airplane CPL: An airplane with an engine rated at more than 200 horsepower, regardless of its equipment.
Histotoxic hypoxia PPL: Hypoxia caused by the cells' inability to use the oxygen delivered to them, typically from alcohol or drugs.
Hold for release IFR: A restriction prohibiting takeoff until ATC explicitly releases the flight, independent of having already received the clearance.
Hold-in-lieu of procedure turnHILPT IFR: A holding pattern depicted at a dual-purpose IF/IAF that substitutes for a procedure turn; flown only when a course reversal is actually needed to establish inbound.
Hold-in-lieu-of-procedure-turnHILPT IFR: A standard holding pattern flown at an IF/IAF as the course-reversal maneuver on an RNAV approach, in place of a conventional procedure turn.
Holding out PPL: Offering a transportation service to the public, which shifts an operation under the air-carriage rules.
Holding position markings PPL: The painted line beyond which the airplane is clear of the runway; the point after which after-landing items may begin.
Hot Spot PPL: A location on an airport diagram, marked with an open circle, that has a documented history of runway incursions or confusing geometry.
Hypemic hypoxia PPL: Hypoxia caused by the blood's inability to carry enough oxygen, most commonly from carbon monoxide, anemia, or recent blood loss.
Hyperventilation PPL: Excessive rate and depth of breathing that causes an abnormal loss of carbon dioxide from the blood.
Hypoxic hypoxia PPL: Hypoxia caused by an insufficient supply of oxygen to the body as a whole, typically from reduced partial pressure of oxygen at altitude.

I

ICAO Cold Temperature Error Table IFR: A table giving the altitude correction, in feet, for a given reported temperature and height above the reporting station.
Immediate action items PPL: The short list of emergency steps a pilot performs from memory before reading the checklist that verifies them.
Impact icing PPL: Ice forming on the exterior of the aircraft that blocks an air intake, possible on both carbureted and fuel-injected engines.
Impending stall PPL: The angle of attack has produced a stall warning, buffet, shaker or horn, but has not yet reached the critical angle.
IMSAFEIllness, Medication, Stress, Alcohol, Fatigue, Emotion PPL: A self-evaluation checklist a pilot runs before every flight.
In-slotin-slot position IFR: For Category C/D turbine airplanes, being wings level on an approximately three-degree descent path not less than 1 NM from the intended touchdown point during the circling maneuver.
Incipient phase PPL: From the stall and start of rotation until the spin fully develops, typically two to four turns; recovery is initiated before 360 degrees of rotation.
Indicated altitude PPL: The altitude read directly off the altimeter with the current local altimeter setting dialed in.
Induced drag PPL: Drag that is an unavoidable byproduct of producing lift, caused by the spanwise flow that creates wingtip vortices. Grows as AOA increases.
Information overload IFR: A named EFB limitation: layered products that raise cognitive workload instead of lowering it.
Initial approach fixIAF IFR: The fix where the initial segment of an instrument approach begins, often with a published holding pattern and speed limit.
Instructor endorsement CPL: An authorized instructor's signature certifying the required instruction was given and the candidate is ready to test.
Instrument currencyRecent instrument experience IFR: The set of tasks under 61.57(c) that must be accomplished within the preceding six calendar months to exercise IFR privileges.
Instrument flight deck check IFR: The sequence of checks of every instrument and its power source, run before any flight involving control by instrument reference.
Instrument proficiency checkIPC IFR: An inflight evaluation by a qualified instrument flight instructor, using instrument rating practical test tasks, that restores IFR privileges after more than twelve months of inactivity.
Instrument rating IFR: An addition to a private or commercial pilot certificate authorizing flight under IFR and in weather below VFR minimums.
Instrument scan IFR: The habitual, repeated cross-check of the flight instruments that catches an attitude change before it becomes an unusual attitude.
Intercept angle IFR: The angular difference between the heading flown and the desired course, chosen to close on the course without overshooting it.
Interception CPL: A military or law enforcement aircraft taking position on an unidentified or non-communicating aircraft; the intercepted pilot follows, rocks wings, uses 121.5 MHz and squawks 7700.
Intermediate fixIF IFR: The fix marking the start of the intermediate segment, where the aircraft aligns with and descends toward the final approach course.
International Standard AtmosphereISA PPL: The reference atmosphere: 15 degC and 29.92 inHg at sea level, with a defined temperature and pressure lapse rate, against which performance data is standardized.
Interpolation CPL: Computing an intermediate value between two published data points, typically by averaging them proportionally.
Inversion IFR: A layer in which temperature increases with altitude instead of decreasing, resisting vertical motion and trapping moisture and haze beneath it.
ISAInternational Standard Atmosphere PPL: The fixed reference model of pressure and temperature by altitude (29.92 inHg and 15 C at sea level) that altimeters and performance charts are calibrated against.
Isobaric mode CPL: The pressurization regime in which the controller holds a constant selected cabin altitude despite the airplane's own climb, used below the maximum differential.
Isogonic line PPL: A line on the chart connecting points of equal magnetic variation; the line of zero variation is the agonic line.
IVSIinstantaneous vertical speed indicator PPL: A VSI fitted with an accelerometer that removes most of the several-second lag of a standard VSI.

J

Jet routeJet route (J-route) IFR: A high-altitude route existing only in Class A airspace, from 18,000 feet MSL to FL450, built on NAVAIDs up to 260 NM apart.

K

Keel effect PPL: A high-wing airplane's tendency to roll back level in a sideslip because most of its side-facing area sits above the CG, like a ship's keel.
Knowledge test validity CPL: The 24 calendar month period during which a passing result allows the candidate to sit for the practical test.
KOELKinds of Operations Equipment List PPL: A list, in the aircraft flight manual, of equipment required for a given type of operation.
Kollsman windowbarometric scale window PPL: The altimeter's small window where the pilot dials in the reference barometric pressure.

L

L over D maxL/DMAX PPL: The minimum drag speed; above it more power is needed to go faster, below it more power is needed to go slower.
L/D maxMaximum lift-to-drag ratio CPL: The angle of attack at which lift divided by drag is greatest; the point of minimum total drag, best glide, and maximum range for a propeller airplane.
L/DMAXMaximum lift-to-drag ratio PPL: The airspeed at which total drag is smallest and lift-to-drag ratio is highest; the best-glide speed with no power.
LAHSOLand and Hold Short Operations PPL: An ATC procedure allowing simultaneous operations on intersecting runways; the pilot-in-command may always decline the clearance.
Land and hold short operationsLAHSO CPL: An ATC procedure at intersecting runways in which a landing aircraft agrees to stop before the intersecting runway; the pilot may decline.
Landing expectancy PPL: The anticipatory belief that conditions are not as threatening as they are and that the approach is sure to end in a safe landing; one of the two named causes of a delayed go-around.
Lapse rate IFR: The rate at which temperature decreases with an increase in altitude: 2 degrees C per 1,000 feet on average, 3 degrees C dry adiabatic, 1.1 to 2.8 degrees C moist adiabatic.
Latent heat of evaporation IFR: The heat absorbed from the nearest available source when liquid water changes to vapor, and released again when the vapor condenses.
Lateral axis PPL: The wingtip-to-wingtip axis about which an airplane pitches, controlled by the elevator.
Lazy eight CPL: Two opposite 180-degree turns, each combining a climbing and a descending 90-degree segment, with pitch, bank, and airspeed all continuously changing.
Lead radiallead-in radial IFR: A charted radial, shown as a thin line, marking where a pilot should begin turning off a DME arc to intercept the next course, used when the turn exceeds 90 degrees.
Lean of peakLOP PPL: A mixture setting leaner than peak EGT, used for economy on engines and installations approved for it.
Leaning PPL: Manually reducing fuel flow with the mixture control to compensate for the lower air density found at altitude.
Leeward CPL: The side of a ridge the wind blows away from and down; it produces increasingly turbulent, terrain-following flow and can push an airplane toward the mountainside.
Lenticular cloudlenticularus CPL: A lens-shaped cloud that forms over mountains in strong winds, appearing motionless because it continuously re-forms on the upwind edge of a wave crest.
Letter of AgreementLOA IFR: A negotiated agreement between two facility managers fixing the location and altitude for handoffs at their shared airspace boundary.
Lift PPL: The force produced by the wing, acting perpendicular to the relative wind, that opposes weight in level flight.
Light gun signals PPL: Signals sent by the tower to an aircraft without a radio, with different meanings in flight versus on the ground.
Limit load PPL: The load factor beyond which the structure suffers permanent deformation.
LNAV/VNAVLateral and Vertical Navigation IFR: An APV line flown to a DA, using WAAS or approach-approved Baro-VNAV, with wider protection than LPV and a possible cold-temperature restriction on Baro-VNAV systems.
Load factorn, in Gs PPL: The ratio of the lift the wing is producing to the airplane's weight. n = 1 in straight, unaccelerated flight.
Loadmeter CPL: An instrument showing the total percentage of load placed on the alternator or generator's capacity by all electrical accessories and the battery.
LOC approachLocalizer approach IFR: A non-precision approach using the localizer signal without a glideslope, flown to a minimum descent altitude.
LocalizerLOC IFR: The VHF component of the ILS providing lateral guidance, transmitting 108.10-111.95 MHz on odd tenths, about 2.5 degrees full-scale deflection each side of the runway centerline.
Localizer-type directional aidLDA IFR: An aid with localizer-comparable signal accuracy, not part of a complete ILS, whose course is offset from the runway centerline.
Locator outer markerLOM IFR: A low-power NDB collocated with an ILS outer marker, sometimes also used, as at Peoria, as the initial and final approach fix for an NDB approach.
Logbook endorsement CPL: A signed, dated entry certifying a pilot's proficiency on a category of airplane; carries no expiration date and requires no test.
Longitudinal axis PPL: The nose-to-tail axis about which an airplane rolls, controlled by the ailerons.
Low-level wind shear PPL: A sudden, drastic change in wind speed or direction over a small area near the ground, associated with fronts, thunderstorms, inversions and strong winds aloft.
LPLocalizer Performance IFR: A WAAS-only line providing angular lateral guidance with no vertical guidance, flown to an MDA, being phased out at most locations.
LPVLocalizer Performance with Vertical guidance PPL: A WAAS-enabled approach type providing vertical guidance and minimums as low as 200 ft HAT at qualifying airports, without ground equipment at the airport.
LUAWLine Up and Wait PPL: An ATC instruction to enter the runway and hold in position; it is not a clearance for takeoff.

M

Mag drop PPL: The decrease in rpm observed when the engine runs on a single magneto instead of both, checked against AFM/POH limits during the runup.
Magnetic bearingMB IFR: The direction to or from a station measured relative to magnetic north, equal to magnetic heading plus relative bearing.
Magnetic dip PPL: The angle at which the Earth's magnetic field lines point into or out of the ground away from the magnetic equator; the underlying cause of the compass's turning and acceleration errors.
Magneto PPL: A self-contained, engine-driven generator that supplies high-voltage current to the spark plugs, independent of the aircraft electrical system.
Maneuvering speedVA CPL: The maximum speed at which full or abrupt control deflection will not exceed the design load limit; it is an upper bound on turn speed, not a target airspeed to fly at.
Manifold pressureMAP PPL: The pressure of the fuel-air mixture in the intake manifold; the power indicator on constant-speed installations.
Master switch PPL: The main electrical switch, typically split into separate battery and alternator halves.
Maximum authorized altitudeMAA IFR: The highest altitude on a route at which reliable navigation signal reception is assured.
Maximum demonstrated crosswind PPL: The strongest crosswind used during the manufacturer's flight testing of the aircraft, published in the POH as an operational reference, not a structural limit.
Maximum elevation figure CPL: The number in each sectional chart quadrangle giving the altitude that clears the highest terrain or obstacle in that box, in thousands and hundreds of feet.
Maximum holding airspeedMHA IFR: The fastest indicated airspeed permitted in a holding pattern at a given altitude, designed to keep the aircraft inside the protected holding airspace.
Maximum performance maneuver PPL: A takeoff or landing flown at the limit of the airplane's capability: shortest roll, steepest climb, slowest touchdown.
MEAMinimum En Route Altitude IFR: The lowest published altitude that guarantees navigation signal reception and obstacle clearance along a route segment.
MELMinimum Equipment List PPL: An approved list of equipment that may be inoperative on a specific aircraft, backed by a letter of authorization.
METARMeteorological Aerodrome Report PPL: A routine, hourly surface weather observation report in standardized format.
MFDmulti-function display PPL: The secondary glass-cockpit screen showing engine data, moving map, charts, weather, and traffic.
MIAMinimum IFR Altitude IFR: A general term for the lowest altitude usable under IFR in a given area (MEA, MOCA, MVA, or a similar published minimum), referenced alongside the MVA for vectored visual approach minimums.
Microburst PPL: A small, intense, short-lived downdraft that spreads out at the surface, producing severe, rapidly reversing wind shear.
Minimum crossing altitudeMCA IFR: A charted altitude a pilot must reach by a specific fix, usually where a higher MEA begins ahead due to terrain.
Minimum descent altitudeMDA IFR: The lowest altitude authorized on a non-precision approach or during circling, with no electronic glidepath; a hard floor with no overshoot allowance.
Minimum en route altitudeMEA IFR: The charted altitude guaranteeing both obstacle clearance and reliable navigation signal along an airway or route segment.
Minimum equipment listMEL IFR: An aircraft-specific approved document listing which equipment may be inoperative, and under what conditions, for a given flight.
Minimum fuel IFR: A specific advisory to ATC that fuel has reached a state where any undue delay cannot be accepted, said plainly rather than assumed from context.
Minimum obstruction clearance altitudeMOCA IFR: The charted altitude matching MEA's obstacle clearance, but guaranteeing signal reception only within 22 NM of the defining NAVAID.
Minimum reception altitudeMRA IFR: The lowest altitude at which an intersection can be reliably identified from an off-course NAVAID.
Minimum Safe AltitudeMSA IFR: An emergency-use-only altitude, shown as a circle on an approach chart, that guarantees obstacle clearance within a stated radius of a facility.
Minimum sink speed CPL: The airspeed giving the lowest rate of altitude loss; a few knots below best glide, with less distance; used when time in flight matters more than distance.
Missed approach pointMAP IFR: The point at which the missed approach procedure must begin if the visual references are not acquired; the DA itself on a PA/APV approach, or a separately identified fix, NAVAID, or time on an NPA.
MOAMilitary Operations Area PPL: A military training zone, open to VFR flight but with a high risk of fast-moving traffic.
Mode C CPL: The transponder mode that reports pressure altitude to ATC and to other aircraft's collision-avoidance systems.
Mode C veil PPL: The 30 NM cylinder around a Class B primary airport within which a Mode C transponder is required.
Moment PPL: The product of an item's weight and its arm, in pound-inches; sometimes divided into a moment index for readability.
Mountain wave CPL: A standing oscillation of air downwind of a ridge, produced when strong wind crosses the terrain beneath a stable layer aloft.
MVAMinimum Vectoring Altitude IFR: The lowest altitude, shown on a controller's facility map, at which ATC may vector an IFR aircraft in a given area, used as the reference for a vectored visual approach's ceiling requirement.

N

NA (alternate minimums not authorized)Alternate minimums NA IFR: A chart notation prohibiting use of an airport, or a specific approach, as an alternate -- often because weather reporting or NAVAID monitoring is unavailable.
Negative contact IFR: The standard phrase confirming to ATC that a pilot in IMC cannot see traffic that has been called out.
Night (14 CFR 1.1)night CPL: The period between the end of evening civil twilight and the beginning of morning civil twilight, as published in the Air Almanac.
Night currency61.57(b) currency CPL: Three full-stop takeoffs and landings within the preceding 90 days, as sole manipulator, between 1 hour after sunset and 1 hour before sunrise, required to carry passengers at night.
No-gyro vector IFR: ATC-issued heading guidance given as "turn left/right" and "stop turn" calls, used when a pilot has no reliable heading reference of their own.
Non-precision approach IFR: An approach providing lateral course guidance only, flown to a minimum descent altitude with no electronic glidepath.
Nondirectional beaconNDB IFR: A ground radio beacon transmitting an omnidirectional signal on low or medium frequency, in the range of about 190 to 535 kHz.
NoPTno procedure turn IFR: A label on a route or IAF indicating no course reversal is required or authorized from that direction of arrival.
Normal maneuvers, normal descent rate IFR: The 91.175 requirement that the aircraft remain continuously positioned for a landing using ordinary flying technique, not an abrupt correction at the last moment.
NOTAMNotice to Airmen PPL: Time-critical aeronautical information, temporary or too recent for publication, disseminated through the National NOTAM System.
NOTAM (D) PPL: A NOTAM given distant dissemination, covering navigational facilities and public-use airports, seaplane bases, and heliports; always begins with a required keyword.
Notice of Disapproval CPL: The document issued on a failed practical test, naming the unsatisfactory tasks and forming the basis for retesting.
Notices to Airmen PublicationNTAP IFR: FAA publication listing current NOTAMs, including the list of Cold Temperature Restricted Airports and their threshold temperatures.
NTAPNotices to Airmen Publication PPL: The baseline NOTAM publication, republished every 28 days.
NTSB Part 83049 CFR Part 830 PPL: The regulation requiring notification of certain accidents and serious incidents and preservation of the wreckage.

O

OBSOmni Bearing Selector PPL: The course selector dial of a VOR receiver.
Obstacle Departure ProcedureODP IFR: A departure procedure developed solely to provide obstacle clearance; it carries no ATC-related climb requirements.
Occluded front PPL: A front formed when a faster cold front overtakes a slower warm front ahead of it, lifting the warm air off the surface.
Off-center viewing PPL: A scanning technique of looking 5 to 10 degrees away from an object at night so the more sensitive peripheral rods can detect it.
Off-route obstruction clearance altitudeOROCA IFR: An off-route altitude providing a 1,000-foot (2,000-foot in mountainous terrain) obstacle buffer, without any guarantee of signal, radar, or communications coverage.
Oil pressure PPL: The pressure of oil circulating through the engine; a drop signals a real or imminent lubrication failure.
On-speed CPL: The governor state in which engine rpm exactly matches the rpm set by the propeller control; no blade angle correction is being made.
One-way strip CPL: A runway operated in a single fixed direction because slope or terrain make the opposite direction unsafe or unusable, regardless of wind.
Operational control CPL: The exercise of authority over initiating, conducting, and terminating a flight; whoever exercises it is the operator in the regulatory sense.
Operations specificationsOperations specifications (OpSpecs) CPL: A document unique to each certificated operator, listing exactly what routes, aircraft, and operations it is approved to conduct.
Otto cycleFour-stroke cycle PPL: The intake-compression-power-exhaust sequence completed over two crankshaft revolutions in a four-stroke engine.
Outflow valve PPL: The valve that regulates air leaving a pressurized cabin, maintaining a cabin altitude of about 8,000 feet at cruise.
Overbanking tendency PPL: At steep bank angles, the airplane continues rolling into the bank unless deliberate opposite aileron pressure is held.

P

P-factorAsymmetric propeller loading PPL: A left-yawing tendency at high AOA, caused by the descending propeller blade producing more thrust than the ascending blade.
P-lead PPL: The wire that grounds a magneto's primary circuit to stop it firing; if it is broken, the magneto stays live even with the switch OFF.
P-staticPrecipitation static IFR: Static electricity that builds up as an aircraft encounters rain or snow particles and discharges from the airframe's extremities, degrading radios and the magnetic compass.
PAPIPrecision Approach Path Indicator PPL: A single row of lights, usually on the runway left side, showing red and white segments to indicate glidepath position.
Parasite drag PPL: Drag not associated with producing lift: form, interference, and skin-friction drag. Grows with the square of airspeed.
Partial panel PPL: Flying without the attitude or heading indicator, using airspeed, vertical speed, turn coordinator, and magnetic compass instead.
Passenger briefing CPL: The briefing 14 CFR 91.107 requires on safety belts and shoulder harnesses, extended by a commercial pilot to doors, exits, emergency equipment and what to do if the pilot is incapacitated.
PAVEPilot, Aircraft, enVironment, External pressures PPL: A risk-management checklist that widens preflight planning beyond the pilot alone.
Personal minimums PPL: Numeric limits set by a pilot in advance, while calm, that are stricter than the regulatory minimums.
PFDprimary flight display PPL: The main glass-cockpit screen combining attitude, airspeed, altitude, heading, and vertical speed in one display.
Pilot in commandPIC PPL: The person vested with final authority and responsibility for the conduct of the flight, under 91.3.
Pilot reportPIREP IFR: An in-flight report of observed conditions - ride, icing, cloud tops - built from aircraft type, location, altitude, and the condition observed.
Pilot-controlled lighting PPL: A system letting a pilot turn on an uncontrolled airport’s lighting with radio clicks on the CTAF.
Pilotage PPL: Navigation by direct reference to landmarks identified on the chart.
PIREPPilot Report PPL: A report of observed weather conditions made by a pilot in flight; coded UA (routine) or UUA (urgent).
Pitot-static system IFR: The combination of the pitot tube and the static ports that feeds the airspeed indicator, altimeter, and vertical speed indicator.
Pivotal altitude CPL: The height above the pylon at which the sighting reference line appears to pivot on the pylon: groundspeed squared, divided by 11.3 (knots) or 15 (mph).
Placard PPL: The INOPERATIVE label placed on deferred equipment under 91.213(d), which removes the item from the pilot's scan before the flight rather than during it.
Position lights PPL: Red left, green right, and white tail navigation lights, required from sunset to sunrise.
Postflight inspection PPL: The walkaround performed after shutdown, looking for fluid streaks, gear and tire damage, and obstructions.
Power, attitude, configuration CPL: The three cardinal principles of the go-around in the order the Airplane Flying Handbook gives them.
Practical slip limit PPL: The bank at which full rudder is needed to hold heading; further bank would turn the airplane despite full opposite rudder.
Practical testAlso called a checkride PPL: The oral and flight examination conducted by a designated pilot examiner, graded against the Airman Certification Standards (ACS).
Pre-ignition PPL: Spontaneous ignition of the fuel-air mixture before the spark fires, usually caused by a hot spot such as a carbon deposit or a cracked plug insulator.
Precautionary landing PPL: A premeditated landing, on or off an airport, when further flight is possible but inadvisable; deteriorating weather is a named cause.
Precession PPL: A gyroscope's response to an applied force, felt 90 degrees later in the direction of rotation rather than at the point of application.
Precision approachPA IFR: An instrument approach providing course and glidepath guidance meeting the ICAO Annex 10 precision standard: ILS, GLS, and PAR.
Preflight action PPL: The information a pilot in command must gather before a flight under 14 CFR 91.103: weather, fuel requirements, alternatives, and known ATC delays.
Pressure altitude PPL: Height above the plane where pressure equals 29.92 inHg; the entry value for most performance tables and charts.
Prevailing visibility IFR: The greatest horizontal visibility equaled or exceeded over at least half the horizon circle, as determined by a ground observer or automated station.
Preventive maintenance CPL: Simple or minor preservation operations and replacement of small standard parts, listed in part 43 appendix A, which a certificated pilot may perform on an aircraft they own or operate.
Private carriage CPL: A specific, individually negotiated arrangement with one customer or a small closed group, without holding out to the public at large.
Pro rata share PPL: The minimum portion of expenses a private pilot must pay: the total divided by the number of occupants.
Procedure turnPT IFR: A maneuver used to reverse course and establish an aircraft inbound on the intermediate or final approach course, flown as a 45/180, 80/260, racetrack, or teardrop shape on the charted maneuvering side.
Proficiency CPL: The skill to fly the airplane and the mission to standard; not defined by regulation and not proved by being current.
Progressive taxi PPL: Step-by-step taxi instructions provided by ATC as the airplane moves, requested when unsure of the route.
Prominent ground feature PPL: A recognizable point used to start a diversion, so the estimate begins from a known position.
Propeller governor CPL: A pump-and-flyweight assembly that holds the pilot-selected rpm by directing engine oil pressure to change propeller blade angle.
Published missed approach IFR: The charted altitude, course, and holding fix that protect an aircraft climbing away from an approach that was not completed.
Pylon CPL: A prominent ground reference point around which the figure-eight pattern is flown.

Q

Quartering tailwind PPL: A wind from behind and to one side, the condition most likely to hold wake vortices along the runway and final approach.

R

Radar contact / radar contact lost IFR: The phrases that start and stop the requirement for compulsory-point position reporting.
Radar traffic advisories CPL: Traffic calls by clock position, distance, direction and type, provided to VFR aircraft in radar contact; a supplement to see and avoid, never a substitute.
Radial PPL: A magnetic bearing line extending outward from a VOR station, independent of the aircraft's heading.
Radiation fog PPL: Fog that forms on clear, calm nights as the ground radiates heat away and cools the air directly above it.
Radius of turn PPL: The size of the circle flown; proportional to the square of the velocity, so doubling airspeed quadruples the radius at a given bank.
RAIMReceiver Autonomous Integrity Monitoring PPL: A GPS receiver function that checks the plausibility of its own position solution using redundant satellite measurements; needs 5 satellites to detect a fault, 6 to exclude it (one fewer of each with baro-aiding).
Random RNAV route IFR: A direct, ATC-approved point-to-point route based on aircraft RNAV capability, requiring radar monitoring but pilot-flown navigation.
Rate of turnROT PPL: Degrees of heading change per second, a function of bank angle and airspeed: about 5.25 degrees per second at 120 knots and 30 degrees of bank.
Readback PPL: Repeating the critical elements of a control instruction back to the controller to catch a misunderstanding.
Recent flight experiencecurrency CPL: The takeoffs and landings 14 CFR 61.57 requires within the preceding 90 days before a pilot may carry passengers, by day or by night.
Rectangular course PPL: The principal ground reference maneuver: equal distance from all four sides of a rectangular reference, flown to replicate the airport traffic pattern.
Red Xinvalid-data flag IFR: A red X drawn across an instrument or value on a glass panel to show the system no longer trusts that data.
Reference point CPL: A prominent point on the horizon, 90 degrees from the entry heading, used to judge the symmetry of the figure.
Region of reverse command PPL: The flight regime, below L/DMAX, in which flying slower requires MORE power to hold altitude, not less.
Region of reversed command CPL: The speed range below the best-endurance speed, down to stall speed, in which holding altitude at a slower airspeed requires more power rather than less.
REILRunway End Identifier Lights PPL: A pair of synchronized flashing lights at the runway threshold that give rapid identification of the approach end.
Rejected takeoff PPL: Discontinuing a takeoff on the runway, at idle power with maximum braking and directional control, when a pre-chosen airborne point is reached without lift-off or an abnormal situation arises.
Relative bearingRB IFR: The angle, measured clockwise from the nose of the aircraft, between the aircraft heading and the direction to the station.
Relative humidity PPL: The ratio of the actual water vapor in the air to the maximum the air could hold at that temperature, expressed as a percentage.
Remote Communications OutletRCO IFR: An unstaffed radio relay that lets a pilot reach a Flight Service Station from an airport with no direct frequency coverage.
Reserve fuel PPL: The minimum fuel required beyond the flight to the first point of intended landing: 30 minutes by day, 45 minutes at night under VFR (14 CFR 91.151).
Resume own navigation IFR: The instruction that returns navigation responsibility for the cleared route to the pilot after a period of radar vectors.
Reverse sensing IFR: A CDI deflection pointing opposite the correction actually needed, avoided by setting the localizer's front course at the OBS or by using a receiver with reverse-sensing capability.
Rhodopsinvisual purple CPL: The light-sensitive pigment in the rods; bleached out by bright light and regenerated during dark adaptation.
Rigidity in space PPL: The tendency of a fast-spinning gyro to keep its spin axis pointed in a fixed direction, independent of how its mounting moves.
Rime ice PPL: Milky white, rough, brittle ice formed from small supercooled droplets freezing on contact, typically in colder temperature bands.
Risk management element CPL: A risk the candidate must identify, assess, and mitigate for a given task, evaluated through the decisions made.
RNAV routeT-route / Q-route IFR: A charted area navigation route: "T" prefix at low altitude, "Q" prefix at high altitude, depicted in aeronautical blue.
RNAV T-routeT-route IFR: A low altitude RNAV route defined by GPS/RNAV waypoints rather than VOR radials, depicted in blue.
Rods PPL: Peripheral retinal receptors, highly sensitive in dim light, with no color perception, that provide most of night vision.
Roll cloud PPL: A low, horizontal, spinning cloud along the leading edge of an advancing thunderstorm, marking an area of extreme turbulence.
Rollout lead CPL: Beginning the rollout before the target heading is reached, by about half the bank angle in degrees, so wings-level coincides with the heading.
Rotating beaconairport beacon CPL: A flashing light identifying an airport from a distance; its color combination identifies the airport type.
Rotation PPL: The gradual back-elevator input that raises the nosewheel slightly off the runway to establish the lift-off attitude once the flight controls become effective.
Rotation point PPL: The point on the runway where an airplane lifts its nose wheel and becomes airborne, used as a reference for wake avoidance.
Rotor CPL: The severely turbulent zone on the leeward side of a ridge where wave-driven air follows the terrain downward; the term pilots commonly use for this leeward turbulent flow.
Round outFlare PPL: The slow, smooth transition from the approach attitude to the landing attitude, started 10 to 20 feet above the ground.
Runway and terrain slope illusionslope illusion CPL: Upsloping runway or terrain creates the illusion of being higher than actual; downsloping runway or terrain creates the opposite illusion.
Runway entrance lightsREL CPL: Red in-pavement lights along the taxiway centerline at the hold position that illuminate when the runway is unsafe to enter.
Runway environment IFR: Any of the ten visual references listed in 91.175(c)(3), one of which must be visible and identifiable to leave DA/DH or MDA.
Runway gradientrunway slope CPL: The change in runway elevation over its length, expressed as a percentage; positive for an upslope, negative for a downslope.
Runway incursion PPL: Any occurrence in the runway environment creating a collision hazard or a loss of required separation with an aircraft taking off or landing.
Runway width illusion CPL: A narrower-than-usual runway creates the illusion of being higher than actual, producing a lower approach; a wider runway has the opposite effect.
RVRRunway Visual Range IFR: An instrumentally derived value, in hundreds of feet, of the horizontal distance a pilot should see down a specific runway from the approach end.

S

SAFETY briefing PPL: The PHAK passenger briefing list: Seat belts, Air vents, Fire extinguisher, Exits, Traffic and talking, Your questions.
Safety pilot IFR: A qualified pilot occupying the other seat during simulated instrument flight, responsible for the outside lookout the view-limiting device takes away.
Scotopic vision PPL: Vision under low light, using rods only, with no color perception and acuity around 20/200 or worse.
Second-class medical certificate CPL: The certificate required to exercise commercial pilot privileges; its commercial privileges last 12 calendar months.
Secondary stall PPL: A second stall triggered by pulling up too abruptly during recovery from a first stall.
Sectional chart PPL: The primary VFR chart, at 1:500,000 scale, revised semiannually in the conterminous United States.
Segmented circle PPL: A ground installation showing wind direction and pattern turn direction for each runway, readable without a radio.
Self-certification CPL: The pilot's ongoing duty to verify fitness to fly before every flight, independent of the certificate's formal validity.
Service ceiling PPL: The altitude at which an airplane's maximum rate of climb has fallen to 100 feet per minute.
Servo CPL: A hydraulic cylinder and piston that converts fluid pressure into mechanical work; single-acting in one direction only, or double-acting in both.
Shock cooling PPL: An abrupt drop in cylinder temperature, typically from a high-speed descent with power reduced too quickly.
Side-skipping PPL: A series of small bounces during a crosswind roll as the airplane tries to fly and settles back while drifting sideways, imposing severe side loads on the gear.
Sideslip PPL: An intentional slip in which the longitudinal axis stays parallel to the original flightpath while the airplane drifts toward the low wing; the crosswind landing technique.
Sighting reference line CPL: An imaginary line from the pilot's eyes, parallel to the lateral axis, used to judge position relative to the pylon; not necessarily the wingtip.
SIGMETSignificant Meteorological Information PPL: An advisory covering severe, non-convective weather hazards significant to all aircraft, identified alphabetically from November through Yankee.
Simplified directional facilitySDF IFR: A directional aid with a fixed beam width of 6 or 12 degrees, possibly offset from the runway, providing no vertical guidance.
Simulated instrument time CPL: Instrument flying performed with a device that restricts outside vision, with a qualified instructor or safety pilot aboard.
Sinus block PPL: A sinus opening plugged by congestion as the pressure difference grows, usually on descent, producing severe pain over the sinus.
Skid PPL: Uncoordinated flight with the ball toward the outside of the turn, caused by excessive rudder for the bank angle in use.
Slaved gyrocompass IFR: A heading indicator corrected automatically from a remote magnetic sensor, checked for slaving action against known headings.
SLDSupercooled large droplets IFR: Large, liquid droplets below 0C, found in or below clouds, that produce rapid clear icing outside any aircraft's certification envelope.
Slip PPL: Uncoordinated flight with the ball toward the inside of the turn, caused by insufficient rudder for the bank angle in use.
Slotted flap PPL: The most common flap: a duct between the flap well and the flap ducts high-energy air over the upper surface, delaying separation and raising maximum lift far more than a plain or split flap.
Slow flight PPL: Maneuvering at an airspeed at which the airplane is still capable of controlled flight without activating the stall warning.
Somatogravic illusion CPL: A rapid acceleration felt as a nose-up pitch, which can prompt a disoriented pilot to push the nose down.
Spatial disorientation PPL: The loss of correct orientation with regard to the position, attitude, or movement of the airplane in space.
SPECI PPL: A special weather report issued between routine METARs when conditions change significantly.
Special flight permitFerry permit PPL: A one-time authorization to move a nonconforming aircraft to a place where it can be repaired.
Special VFR PPL: 1 SM visibility and clear of clouds, within surface-designated airspace. At night it requires an instrument rating.
Specific range PPL: A measure of fuel efficiency, expressed as nautical miles flown per gallon or per pound of fuel.
Speed instability PPL: The behaviour below minimum drag speed in which a decrease in airspeed tends to continue unless the pilot reduces angle of attack or adds power.
Spin PPL: An aggravated stall in which the airplane follows a downward corkscrew path, rotating about its vertical axis with at least one wing stalled.
Spiral dive PPL: A descending turn that tightens and accelerates on its own; pulling before levelling the wings makes it worse.
Spiral instability PPL: A slow, gradually steepening descending spiral caused by directional stability that is strong relative to dihedral.
Squall line PPL: A continuous, often violent line of thunderstorms that can form as far as 200 miles ahead of a fast-moving cold front.
Squat switchLanding gear safety switch CPL: A switch on a main gear shock strut that opens the retraction circuit whenever the airplane's weight compresses the strut; inactive once weight is off the wheels.
Squawk PPL: The word used by ATC to request a transponder code or function.
St. Elmo's fire IFR: A faint, harmless glow caused by electrical discharge, often seen on the windscreen or wingtips during a P-static buildup.
Stabilized approach PPL: An approach meeting fixed criteria for glide path, heading, airspeed, configuration, descent rate, power, and completed checklists.
Stagnant hypoxia PPL: Hypoxia caused by oxygen-rich blood failing to circulate to the tissues that need it, as with high G-forces or poor circulation.
Stall PPL: A rapid loss of lift caused by airflow separation from the wing when the critical angle of attack is exceeded.
Standard alternate minimumsAlternate minimums IFR: The forecast ceiling and visibility required to file an airport as an alternate: 600-2 with a published precision approach, 800-2 otherwise.
Standard atmosphereISA CPL: The reference model of pressure and temperature versus altitude that all aircraft performance charts are built against: 15°C at sea level, falling roughly 2°C per 1,000 feet.
Standard holding patternright-turn hold IFR: A holding pattern using right turns throughout; the default unless ATC specifies left turns for a nonstandard pattern.
Standard Instrument DepartureSID IFR: An ATC-requested and developed departure route, built primarily to increase capacity and organize traffic flow in busy terminal airspace.
Standard Terminal Arrival RouteSTAR IFR: A published arrival route that organizes traffic flow into a busy terminal area, often built from several transitions merging onto one common route.
Standard-rate turn PPL: A turn of 3 degrees per second: 2 minutes for a complete 360-degree turn.
Standby battery IFR: A battery that powers essential instruments for a limited time after an alternator or generator failure.
Starter duty cycle PPL: The cranking limit of an electric starter: about 30 seconds of continuous operation followed by a cool-down of 30 seconds to a minute, or longer per the AFM/POH.
Static stability PPL: The initial tendency of an airplane to return toward, stay at, or diverge from its trimmed condition after a disturbance.
Static system and altimeter testPitot-static / altimeter test IFR: A 24-calendar-month inspection under 91.411 confirming the altimeter and altitude-reporting equipment remain accurate.
Static wick IFR: A small discharge device on a wingtip, tail, or control surface trailing edge that bleeds off static charge harmlessly before it builds to a discharge.
Stationary front PPL: A frontal boundary where neither air mass is dense enough to displace the other, so the front remains nearly in place.
Steep spiral CPL: A gliding turn of at least three complete 360-degree turns around a ground reference point, flown at idle power with a constant radius and airspeed.
Sterile flight deck PPL: A period with no communication between pilot and passengers in either direction, from departure to the first intermediate altitude and from the first arrival vector to landing.
Stuck microphone CPL: A transmit switch held closed, which blocks the frequency for everyone else and is invisible from the aircraft causing it.
Sublimation IFR: The change from ice directly to water vapor, bypassing the liquid stage; with evaporation, one of the only two processes that add water vapor to the atmosphere.
Suction gauge IFR: The indication of vacuum available to drive the gyro instruments; the check is that suction is appropriate for the instruments in that particular airplane.
Sump PPL: A low point in a fuel tank or fuel line where water and sediment collect and can be drained and inspected.
Surface analysis chart PPL: A chart transmitted every three hours depicting current surface weather: pressure systems, fronts, and station models for reporting points across the country.

T

TAFTerminal Aerodrome Forecast PPL: A forecast of expected conditions within about 5 statute miles of an airport, typically valid 24 hours.
Tailplane stall PPL: A stall of the horizontal stabilizer caused by ice accretion, often triggered by flap extension, producing an uncommanded nose-down pitch opposite the symptoms of a wing stall.
Takeoff hold lightsTHL CPL: Red in-pavement lights on the runway at the departure position that illuminate when the runway ahead is unsafe for takeoff.
Task CPL: An evaluation unit within an Area of Operation, identified by a letter, carrying its references, objective, and elements.
Task management PPL: Completing routine tasks as early as possible so that attention is available in the later, more critical phases of flight.
TDZETouchdown Zone Elevation IFR: The highest elevation in the first 3,000 feet of the landing surface, used as the reference point for HAT and VDP calculations.
Teardrop entryteardrop entry procedure IFR: A holding entry flown by tracking outbound on a 30-degree offset from the inbound course, on the holding side, for 1 minute, before turning to intercept the inbound course.
Technically advanced airplaneTAA CPL: An airplane fitted with an integrated avionics suite: a primary flight display, a multi-function display with a moving map, and a two-axis autopilot coupled to navigation.
Temperature inversion PPL: A layer in which temperature increases with altitude instead of the normal decrease, trapping moisture and pollutants beneath it.
Terminal Arrival AreaTAA IFR: A T-shaped RNAV procedure structure with a straight-in sector and two base sectors, each carrying its own minimum altitude, allowing entry from nearly any direction.
Terminal Radar Approach ControlTRACON IFR: The radar facility handling arrivals and departures in the busier terminal areas, between the tower and Center.
The impossible turnImpossible turn PPL: A low-altitude turn back to the runway after an engine failure on takeoff; high risk of an accelerated stall without specific training.
The leans PPL: A false sensation of banking, felt after leveling the wings following a slow turn that went unnoticed.
Threshold crossing heightTCH IFR: The height of the glidepath above the runway threshold, published on the chart alongside the glideslope angle.
Thrust PPL: The forward force produced by the propeller or engine, opposing drag and acting generally along the longitudinal axis.
Time of useful consciousnessTUC PPL: The maximum time a pilot deprived of oxygen can act rationally and effectively at a given altitude before becoming incapable of useful action.
Tingling sensationParesthesia PPL: A pins-and-needles sensation in the extremities and face, a symptom shared by both hypoxia and hyperventilation.
Torque reaction PPL: Newton's third-law reaction to the engine and propeller's rotation, tending to roll (airborne) or yaw (on the ground) the airplane opposite the propeller's direction of spin.
Total pressuretotal (pitot) pressure PPL: The sum of static and dynamic pressure, captured by the pitot tube facing into the relative wind.
Tower En Route ControlTEC IFR: An ATC program using overlapping approach-control radar to route IFR flights between airport towers without a Center handoff.
Traffic advisory PPL: A controller's call of an observed target by clock position relative to your track, distance, direction of movement, and type and altitude if known.
Traffic pattern altitudeTraffic pattern altitude (TPA) PPL: The published pattern altitude, typically 1,000 feet AGL for light airplanes, higher for large or turbine aircraft.
TransitionSTAR transition IFR: One of several named starting routes onto a STAR, each beginning at a different fix or navaid and converging onto the arrival's common route.
Transponder testATC transponder test IFR: A 24-calendar-month inspection under 91.413 confirming the transponder replies correctly to ATC interrogation.
Trend vector PPL: A magenta line on the airspeed or altitude tape showing a 6-second projection of where the value is heading.
Trim runaway CPL: Electric trim running without command; held with elevator, stopped with the disconnect or breaker, then retrimmed manually.
Trim tab PPL: A small hinged surface on the trailing edge of a primary control that moves opposite to it, relieving the pilot of holding pressure.
TRSATerminal Radar Service Area PPL: An area offering voluntary radar separation to participating VFR aircraft, with a Class D primary airport at its center.
True airspeedTAS CPL: The airplane's actual speed through the air mass; it grows relative to indicated airspeed as density altitude increases, which is why ground roll lengthens even though rotation speed does not change.
True airspeed (TAS) PPL: Calibrated airspeed corrected for altitude and nonstandard temperature; the speed used for flight planning.
True altitude PPL: The actual height of the aircraft above mean sea level (MSL).
True course (TC) PPL: The direction of the line drawn between two points on a chart, measured clockwise from true north.
Turbulence penetration speed IFR: The airspeed published in the POH/AFM that minimizes structural load if severe turbulence is encountered.
Turn radius CPL: The radius of the circular path flown in a turn; it shrinks with a steeper bank angle and grows with higher airspeed at a fixed bank angle.
Turning error IFR: A magnetic compass error, worst near north and south, caused by magnetic dip acting on the compass float assembly during a turn.

U

Ultimate load PPL: The load factor, 1.5 times the limit load, at which the structure actually breaks.
Undesired aircraft state CPL: The airplane at an attitude, airspeed, altitude or heading the pilot did not intend, typically while attention is on a malfunction; the accident forming.
UNICOM PPL: A private airport radio station providing ground services, often also serving as the CTAF.
Unusual attitude PPL: Any pitch or bank the airplane has reached that the pilot did not command, usually after distraction, disorientation or turbulence.
Useful load PPL: Maximum gross weight minus basic empty weight: occupants, usable fuel, drainable oil, and baggage, on a general aviation aircraft.

V

Vacuum (suction) PPL: The pressure differential created by the pump that spins the gyroscopic instruments, measured in inches of mercury.
Vacuum pump PPL: An engine-driven pump that creates the suction used to spin pneumatic gyroscopic instruments.
Vacuum system IFR: The pump-driven suction system that spins the gyros inside a conventional attitude indicator and heading indicator.
Valsalva maneuver CPL: Closing the mouth, pinching the nose and gently blowing to force air up the Eustachian tube and equalize middle ear pressure.
Variation PPL: The angular difference between true north and magnetic north at a given location, shown on charts by isogonic lines.
VASIVisual Approach Slope Indicator PPL: A set of light bars beside the runway that show red or white to indicate whether the airplane is above, below, or on the glidepath.
Venturi PPL: A narrowed throat in the carburetor where accelerating air loses pressure, which draws fuel into the airstream.
Vertical axis PPL: The top-to-bottom axis about which an airplane yaws, controlled by the rudder.
Vertical visibility IFR: The reported height penetrable into a layer that totally obscures the sky, with no defined cloud base -- distinct from a ceiling.
Vestibular system PPL: The balance-sensing organs of the inner ear, which detect acceleration but not steady motion, and become unreliable without visual references.
VFR flight plan PPL: A voluntary filing, held by the FSS for search-and-rescue purposes, activated by reporting an actual departure time and closed by the pilot on arrival.
VFR waypoint PPL: A five-letter, "VP"-prefixed navigation point for VFR use, charted with the same star symbol as IFR waypoints.
Vg diagramV-n diagram PPL: A graph of airspeed against load factor showing an airplane's structural operating envelope, valid for a specific weight and altitude.
Victor airway PPL: A federal airway flown VOR to VOR, charted as a thin magenta line on the sectional.
View-limiting deviceHood / foggles IFR: A device blocking outside visual reference so a pilot can practice or log simulated instrument flight while remaining VFR.
Virga CPL: Rain that evaporates before reaching the ground, cooling the air beneath the cloud and feeding downdrafts.
Visual approachvisual approach clearance IFR: An ATC authorization for an IFR flight to proceed visually to the airport; not an instrument approach procedure, and it has no missed approach segment.
Visual Climb Over AirportVCOA IFR: A departure option letting a pilot climb visually over the airport to a stated altitude, in VMC with a stated visibility minimum, before continuing the departure on instruments.
Visual descent pointVDP IFR: A defined point on final, at or after which a normal descent from the MDA to the runway touchdown zone may begin, provided the required visual references are in sight.
VLEMaximum landing gear extended speed CPL: The maximum speed at which the airplane may be flown with the landing gear down and locked.
VLOMaximum landing gear operating speed CPL: The maximum speed at which the landing gear may be extended or retracted through its cycle.
VNOmaximum structural cruising speed PPL: Upper boundary of the green arc; flight above VNO is permitted only in smooth air.
VOR accuracy checkVOR receiver check IFR: A check required within the preceding 30 days to use a VOR for IFR navigation, logged with date and observed error.
VOR test facilityVOT IFR: A ground facility, or a radiated signal from a rated repair station, transmitting a known signal used to check VOR receiver accuracy.
Vortex decay PPL: The weakening of a wake vortex with time and distance behind the generating airplane; hastened by a dirty aircraft configuration.
VOTVOR Test Facility PPL: A ground facility broadcasting a fixed test signal, tuned at 108.0 MHz, used to check VOR receiver accuracy: 000 FROM or 180 TO.
VREFReference landing speed CPL: A final approach airspeed normally equal to 1.3 times VSO, the stall speed in the landing configuration, adjusted for wind and gusts.
VS0Stall speed, landing configuration PPL: Published stall speed with flaps and landing gear extended, at maximum weight.
VS1Stall speed, specified configuration PPL: Published stall speed in a specified configuration, typically clean (flaps and gear retracted).
VSOpower-off stalling speed, landing configuration CPL: The stalling speed with gear and flaps in the landing configuration; used as 1.4 VSO to decelerate to after throttle closure and 1.3 VSO as a target final approach speed.
VxBest angle of climb speed PPL: The speed that gives the greatest altitude gain per unit of horizontal distance, used to clear an obstacle.
VyBest rate of climb speed PPL: The speed that gives the greatest altitude gain per unit of time, used for a normal climb.

W

WAASWide Area Augmentation System PPL: A differential GPS augmentation system using ground reference stations and geostationary satellites to improve accuracy and provide fast integrity alerts, the basis of LPV approaches.
Wake turbulence PPL: Turbulence, including wingtip vortices, generated by an airplane in flight, hazardous to airplanes flying through it -- especially smaller, slower ones.
Warm front PPL: The boundary where advancing warm air rides up and over retreating cooler air, producing an extensive, slow-moving weather shield.
Washout PPL: A slight built-in twist along the wingspan that gives the wingtip a lower AOA than the wing root, so the root stalls first.
Weeping wing CPL: An ice protection system that pumps antifreeze through small holes in the leading edge to prevent ice from bonding to the airframe and to remove ice already present.
Wind correction angle PPL: The angle between heading and desired ground track that cancels drift.
Wind correction angle (WCA) PPL: The angle applied to the course, into the wind, to make the aircraft's track over the ground coincide with the intended course.
Wind triangle PPL: The vector diagram linking heading and true airspeed, wind direction and speed, and track and groundspeed.
Winds and temperatures aloft forecastFB PPL: A twice-daily forecast of wind direction, speed and temperature at fixed altitudes for specific locations, based on the 0000Z and 1200Z radiosonde observations.
Windward CPL: The side of a ridge the wind blows toward and up; it produces lift that helps carry an airplane over the terrain.
Wing-low methodSideslip method PPL: A crosswind landing technique: bank into the wind, hold the ground track with opposite rudder, upwind wheel touches down first.
Wingtip vortex PPL: The trailing, rotating airflow spilling around a wingtip whenever the wing produces lift; strongest when the generating airplane is heavy, slow, and clean.