Glossary

Automatic Dependent Surveillance-Broadcast, which broadcasts the aircraft's GPS position, altitude, and velocity (ADS-B Out) and can receive traffic and weather (ADS-B In, via FIS-B and TIS-B). ADS-B Out is required in most controlled airspace per 91.225.

The tendency of an aircraft to yaw opposite the direction of a roll, caused by the higher induced drag on the rising (outside) wing as its aileron deflects down. Coordinated rudder input counteracts it.

An Airmen's Meteorological Advisory for weather hazardous to light aircraft: Sierra (IFR/mountain obscuration), Tango (turbulence/strong surface winds), and Zulu (icing/freezing levels). Valid 6 hours and less severe than a SIGMET.

A differential pressure instrument that displays indicated airspeed by comparing ram (pitot) pressure to static pressure. Its color arcs depict the flap operating range (white), normal range (green), caution range (yellow), and Vne (red line).

A legally enforceable FAA regulation issued to correct an unsafe condition in a product. Compliance is mandatory by the specified time or recurring interval, and the owner/operator is responsible for ensuring all applicable ADs are met.

A pressure instrument that displays altitude by sensing static (ambient) air pressure through an aneroid. It must be set to the local altimeter setting (Kollsman window); flying from a high to a low pressure area without resetting causes the altimeter to read higher than actual.

The angle between the wing chord line and the relative wind. The wing always stalls at the same critical angle of attack regardless of airspeed or attitude.

A gyroscopic instrument that displays the aircraft's pitch and bank relative to the horizon, using rigidity in space. It is the primary instrument for attitude control in IMC and is typically vacuum or electrically driven.

An alternative to holding an FAA medical (14 CFR 61.113) allowing flight after one valid medical since July 2006, a state driver's license, a physician exam every 48 months, and an online course every 24 months. Limited to aircraft up to 6 occupants and 6,000 lbs, below 18,000 ft MSL, and 250 knots.

The airspeed that provides the maximum gliding distance for altitude lost (L/D max) with the engine inoperative. Flying faster or slower than best glide reduces range; it decreases slightly with lower weight.

A form of hypemic hypoxia caused by inhaling the colorless, odorless gas in exhaust, often from a cracked muffler/heater. Symptoms include headache, drowsiness, and dizziness; cabin heat should be shut off and fresh air introduced.

Ice that forms in the carburetor venturi due to the temperature drop from fuel vaporization and pressure reduction, restricting airflow and reducing power. It can occur at outside temperatures as high as 70 degrees F with high humidity; carb heat is the cure.

The point at which the aircraft's weight is considered to be concentrated and about which it balances. A forward CG increases stability but raises stall speed; an aft CG reduces stability and can make stall/spin recovery difficult.

Controlled airspace from 18,000 ft MSL up to and including FL600. All operations must be conducted under IFR with an instrument rating, ATC clearance, and Mode C/ADS-B Out; VFR flight is not permitted.

Controlled airspace surrounding the busiest airports, typically from the surface to 10,000 ft MSL and shaped like an upside-down wedding cake. It requires an explicit ATC clearance to enter, two-way radio, Mode C, and ADS-B Out; VFR visibility is 3 SM and clear of clouds.

Controlled airspace around airports with a control tower and radar approach control, generally a 5-nm surface core to 4,000 ft AGL and a 10-nm shelf from 1,200 to 4,000 ft AGL. It requires two-way radio communication established before entry, Mode C, and ADS-B Out.

Controlled airspace around an airport with an operating control tower, typically extending to about 2,500 ft AGL within roughly 4 nm. It requires two-way radio communication established before entry; VFR minimums are 3 SM and the standard 1,000/500/2,000 cloud clearances.

Controlled airspace that is not A, B, C, or D, including most airspace from 1,200 ft AGL (or 700 ft near airports) up to 18,000 ft MSL. No clearance is required for VFR, but IFR operations need a clearance; cloud clearances increase above 10,000 ft MSL.

Uncontrolled airspace where ATC has no authority, generally from the surface up to the overlying Class E floor. VFR minimums are reduced (e.g., 1 SM and clear of clouds during the day below 1,200 ft AGL); no clearance is needed for VFR or IFR.

The leading edge of an advancing cold air mass that forces warmer air up steeply, producing a narrow band of heavy showers, thunderstorms, gusty winds, and rapid clearing behind. Cold fronts move faster than warm fronts.

A significant meteorological advisory for hazardous convective weather affecting all aircraft: severe/embedded thunderstorms, lines of thunderstorms, or areas of heavy precipitation. Issued for the contiguous U.S. and valid up to 2 hours; it implies severe turbulence, icing, and low-level wind shear.

The angle of attack (about 15-20 degrees for many wings) beyond which airflow separates and the wing stalls. It is fixed for a given wing regardless of weight, airspeed, or bank angle.

Navigation by computing heading, groundspeed, and time using a known starting point, true airspeed, wind, and magnetic variation. It is typically combined with pilotage for cross-country flight.

The release of nitrogen bubbles in the body from a rapid pressure decrease. Pilots must wait at least 12 hours after a non-decompression-stop dive (24 hours if a stop dive or if flying above 8,000 ft) before flight to avoid evolved-gas DCS.

Pressure altitude corrected for non-standard temperature -- the altitude the aircraft 'feels.' High density altitude (hot, high, humid) degrades takeoff, climb, and engine performance.

The temperature to which air must be cooled to become saturated and begin condensing moisture. When the temperature-dewpoint spread is small (within about 4 degrees F / 2 degrees C), fog, dew, or low clouds are likely.

Equipment that measures slant-range distance in nautical miles from a ground station. Because it measures slant range, readings are least accurate directly over the station at high altitude (the 'cone of confusion').

The aerodynamic force that opposes the aircraft's motion through the air, acting parallel to and in the same direction as the relative wind. Total drag is the sum of induced drag and parasite drag.

Under 14 CFR 91.17, no person may act as a crewmember within 8 hours of consuming alcohol, while under its influence, with a blood alcohol of 0.04 percent or greater, or while using any impairing drug. Many operators require a longer interval.

The FAA medical certificate required to exercise ATP privileges. For pilots under 40 it is valid 12 calendar months for ATP operations; for those 40 and over, 6 calendar months. It also covers commercial and private privileges for the duration allowed those classes.

Required under 14 CFR 61.56 to act as PIC: within the preceding 24 calendar months, at least 1 hour of ground and 1 hour of flight training with an authorized instructor, plus a logbook endorsement. Formerly called the biennial flight review.

An electronic Primary Flight Display that integrates attitude, airspeed, altitude, heading, and navigation onto a single screen, typically paired with a multifunction display. It uses solid-state air data and attitude reference systems (ADAHRS) rather than spinning gyros.

A satellite-based navigation system that provides precise position, velocity, and time worldwide using a constellation of satellites. Receivers need at least four satellites in view to compute a 3D position fix.

A rejected landing in which the pilot applies full power, establishes a climb, retracts flaps incrementally, and re-enters the pattern. It is a normal safety maneuver to be used any time the landing is not assured.

A temporary reduction in induced drag when the aircraft is within about one wingspan of the surface, caused by the ground interrupting wingtip vortices and downwash. It can allow an aircraft to lift off below normal flying speed and then settle back down.

The distance the aircraft travels along the runway during takeoff before liftoff, or during landing after touchdown until stopped. It increases with high density altitude, weight, tailwind, and upslope.

A property of the spinning propeller acting as a gyroscope, where a force applied to the disc is felt 90 degrees later in the direction of rotation. Raising the tail of a taildragger produces a yawing force to the left.

A gyroscopic instrument that displays magnetic heading without the lead/lag errors of the magnetic compass. It drifts due to precession and friction and must be realigned to the magnetic compass periodically, typically every 15 minutes.

The inability of body cells to use available oxygen, typically caused by alcohol, drugs, or certain poisons. Oxygen delivery is adequate but the tissues cannot metabolize it.

A racetrack-shaped pattern used to delay an aircraft, consisting of inbound and outbound legs and standard right-hand turns unless charted otherwise. Standard timing is 1 minute inbound at or below 14,000 ft and 1.5 minutes above; entries are direct, parallel, or teardrop.

Oxygen deficiency caused by the blood's reduced ability to carry oxygen, as from anemia, blood loss, or carbon monoxide poisoning. The lungs deliver oxygen normally but the blood cannot transport enough of it.

Excessive rate and depth of breathing, often from stress or anxiety, that flushes too much carbon dioxide from the blood. Symptoms (lightheadedness, tingling, cool/clammy feeling) mimic hypoxia; recovery comes from slowing the breathing rate.

Oxygen deficiency caused by insufficient partial pressure of oxygen at altitude, the most common type for pilots. Symptoms (euphoria, impaired judgment, cyanosis, tunnel vision) can begin subtly above 10,000 ft and worsen rapidly higher up.

A personal preflight fitness check: Illness, Medication, Stress, Alcohol, Fatigue, and Emotion/Eating. It helps a pilot decide whether they are physically and mentally fit to fly.

Drag produced as a by-product of lift, caused by wingtip vortices and downwash. It increases as airspeed decreases and angle of attack increases, dominating at low speeds and high angles of attack.

Required inspections for airworthiness: Annual (12 calendar months), VOR check (30 days for IFR), 100-hour (if for hire/flight instruction), Altimeter/pitot-static (24 months for IFR), Transponder (24 months), and ELT (12 months).

The angle of attack and airspeed at which the lift-to-drag ratio is greatest and total drag is at its minimum. It produces maximum glide range, best range airspeed, and corresponds to the bottom of the power-required curve.

The rate at which temperature decreases with altitude. The standard (average) lapse rate is about 2 degrees C per 1,000 ft; the dry adiabatic rate is 3 degrees C per 1,000 ft and the moist adiabatic rate is roughly 1.1-2.8 degrees C.

The aerodynamic force perpendicular to the relative wind, produced primarily by the difference in pressure between the upper and lower wing surfaces. Lift varies with the square of airspeed, angle of attack, air density, and wing area.

ATC visual signals for lost-communication aircraft: steady green means cleared to land/takeoff, flashing green means return to land/cleared to taxi, steady red means stop/give way, flashing red means taxi clear of runway/airport unsafe, flashing white means return to starting point, and alternating red/green means exercise extreme caution.

The ratio of the total lift acting on an aircraft to its actual weight, expressed in Gs. Load factor increases sharply in turns; a 60-degree bank level turn imposes 2 Gs, and stall speed rises with the square root of the load factor.

Under 14 CFR 91.185, fly the route by AVE-F (Assigned, Vectored, Expected, Filed) and the altitude that is the highest of MEA, expected, or assigned (MEA). If in VMC, continue VFR and land as soon as practicable; squawk 7600.

If radio contact is lost in VFR conditions, the pilot squawks 7600, remains clear of clouds, and proceeds to land while watching for ATC light gun signals. The pilot may enter the pattern and acknowledge signals by rocking the wings (day) or flashing the landing light (night).

A simple, self-contained instrument that indicates magnetic heading using a float assembly aligned with the earth's magnetic field. It is subject to variation, deviation, dip errors, and oscillation but is the only required heading source if the gyro fails.

Acceleration and deceleration errors on east/west headings: Accelerate-North, Decelerate-South. On an easterly or westerly heading the compass momentarily shows a turn toward north when accelerating and toward south when decelerating.

Northerly turning error: Undershoot North, Overshoot South. When turning from a northerly heading roll out early (undershoot), and when turning from a southerly heading roll out late (overshoot); the lead/lag roughly equals the latitude.

The angular difference between true north and magnetic north at a given location. Pilots apply variation to convert a true course to a magnetic course (east is least, subtract; west is best, add).

An engine-driven self-contained generator that produces the high-voltage spark for the ignition system independent of the aircraft electrical system. Most aircraft have dual magnetos for redundancy and more complete, efficient combustion.

The maximum speed at which full, abrupt control deflection won't overstress the airframe; the aircraft stalls before exceeding limit load. Va decreases with weight.

An Aviation Routine Weather Report, an hourly observation of conditions at an airport including wind, visibility, weather, sky condition, temperature/dewpoint, and altimeter setting. SPECI reports are issued for significant changes.

An intense, localized downdraft from a convective cloud, typically less than 2.5 miles across and lasting under 15 minutes, producing severe wind shear with downdrafts up to 6,000 ft/min and headwind-to-tailwind shifts that can exceed an aircraft's climb capability.

Special use airspace established to separate military training activities from IFR traffic. VFR aircraft may legally transit an active MOA but should exercise extreme caution and may request traffic advisories from ATC.

The cockpit control that adjusts the fuel-to-air ratio. Leaning at altitude maintains proper combustion as air density decreases, improving efficiency and preventing fouling and roughness from an overly rich mixture.

Vision in low light relies on the rod cells, which are concentrated outside the central fovea, so a slight off-center scan reveals dim objects better. Full dark adaptation takes about 30 minutes and is easily destroyed by bright light.

The asymmetric thrust produced at high angles of attack because the descending propeller blade takes a larger bite of air than the ascending blade. With a clockwise-rotating prop, it yaws the airplane left, requiring right rudder.

Drag not associated with the production of lift, including form drag, skin friction, and interference drag. It increases with the square of airspeed and dominates at higher speeds.

The person who has final authority and responsibility for the operation and safety of the flight (14 CFR 1.1). The PIC may deviate from any rule in an in-flight emergency to the extent required to meet that emergency (91.3).

An in-flight weather report filed by pilots covering conditions such as cloud bases/tops, turbulence, icing, and wind. UA denotes a routine report and UUA an urgent one (e.g., severe icing or turbulence, wind shear).

Navigation by visual reference to landmarks and checkpoints on the ground compared against a sectional chart. It is most reliable over terrain with distinctive features and good visibility.

The system supplying ram air and static (ambient) pressure to the pitot-static instruments. The pitot tube feeds the airspeed indicator while the static port feeds the altimeter, VSI, and airspeed indicator.

Under 14 CFR 91.103, before any flight the PIC must become familiar with all available information concerning that flight, including weather, fuel requirements, alternatives if the planned flight cannot be completed, runway lengths, and takeoff/landing distance data.

Fog that forms on clear, calm nights when terrestrial radiation cools the ground and the air just above it to the dewpoint. Common in low-lying areas and valleys, it typically burns off after sunrise.

Under 14 CFR 61.57, to carry passengers a pilot must have made 3 takeoffs and landings in the preceding 90 days in the same category, class, and type (if required); night currency requires those landings to be to a full stop between 1 hour after sunset and 1 hour before sunrise.

The slow-speed flight regime (behind the power curve) where more power is required to fly slower because induced drag rises rapidly. Common during slow flight and short final, where pitch controls airspeed and power controls altitude.

Documents required aboard the aircraft: Airworthiness certificate, Registration, Radio station license (international only), Operating limitations (POH/placards), and Weight and balance data. The first two must be displayed or accessible per 91.203 and 91.9.

Special use airspace containing hazards such as artillery firing, aerial gunnery, or missiles. Flight is prohibited when the area is active (hot) without permission from the controlling agency; charted hours are listed on the sectional.

Under 14 CFR 91.113, an aircraft in distress has the right of way over all others. In converging traffic the aircraft on the right has the right of way; aircraft must give way in this least-to-most maneuverable order: balloon, glider, airship, airplane/rotorcraft, then aircraft towing or refueling.

Any unauthorized presence of an aircraft, vehicle, or person on a runway protected area. Prevention relies on a clear taxi clearance, airport diagram review, sterile cockpit, and never crossing a hold-short line without explicit clearance.

A VFR aeronautical chart at 1:500,000 scale showing terrain, airspace, airports, navaids, and obstacles. It is the primary chart for VFR cross-country flight and is revised on a regular cycle.

The maximum density altitude at which the aircraft can still climb at a specified minimum rate (100 ft/min for piston singles). Above it, climb performance becomes marginal; the absolute ceiling is where climb rate reaches zero.

A Significant Meteorological Advisory for non-convective weather hazardous to all aircraft, such as severe turbulence, severe icing, widespread duststorms or sandstorms, or volcanic ash. Valid up to 4 hours (6 for volcanic ash).

A false sensation caused by linear acceleration or deceleration felt by the vestibular system. Rapid acceleration on takeoff can feel like a nose-high pitch, tempting the pilot to push the nose down toward the ground.

The inability to determine one's position, attitude, and motion relative to the earth, caused by conflicting or false signals from the vestibular, visual, and proprioceptive systems. Trusting the flight instruments over bodily sensations is the primary defense.

An ATC clearance allowing a VFR flight to operate within surface-based controlled airspace below standard VFR minimums (at least 1 SM visibility and clear of clouds). It must be requested, and at night requires an instrument rating and instrument-equipped aircraft.

An aggravated stall in which the aircraft descends in a corkscrew path with one wing more stalled than the other (autorotation). Recovery follows PARE: Power idle, Ailerons neutral, Rudder opposite the spin, Elevator forward.

The corkscrewing flow of air from the propeller that wraps around the fuselage and strikes the left side of the vertical stabilizer, yawing the nose left. It is one of the four left-turning tendencies.

Oxygen deficiency caused by inadequate blood circulation, such as from excessive G-forces, cold, or a heart problem. Oxygen-rich blood is not moving fast enough to meet tissue demand.

A sudden loss of lift and increase in drag that occurs when the wing exceeds its critical angle of attack and the smooth airflow separates from the upper surface. A stall can happen at any airspeed, attitude, or power setting.

The internationally agreed reference atmosphere with a sea-level temperature of 15 degrees C, pressure of 29.92 in Hg (1013.2 hPa), and a standard lapse rate of 2 degrees C per 1,000 ft. Performance charts are based on ISA conditions.

A turn at 3 degrees per second, completing a 360-degree turn in two minutes. Indicated on the turn coordinator and used heavily for instrument flying.

Ice that accumulates on the airframe when flying through visible moisture (clouds or precipitation) at temperatures at or below freezing. Clear ice is dense and hard to remove; rime ice is rough and opaque; mixed ice combines both.

Under 14 CFR 91.211, the required minimum flight crew must use oxygen above 14,000 ft MSL cabin pressure altitude, and for the portion of flight more than 30 minutes above 12,500 ft up to 14,000 ft. Above 15,000 ft MSL, oxygen must be provided to all occupants.

An atmospheric layer where temperature increases with altitude instead of decreasing. Inversions create stable air that traps moisture and pollutants, often causing haze, fog, and smooth but poor-visibility conditions; wind shear can exist at the top.

A regulatory action that temporarily restricts aircraft operations in a defined area, issued for hazards, security (e.g., presidential movement), sporting events, or disaster relief. Pilots must check NOTAMs before flight to avoid violating an active TFR.

A coded forecast for the area within 5 statute miles of an airport, typically valid 24 or 30 hours and issued four times daily. It uses the same elements as a METAR plus change groups like TEMPO, BECMG, and FM.

The most common vestibular illusion, where a too-slow roll back to level is not detected, leaving the pilot feeling the wings are banked when level. Pilots may lean to one side to feel upright while the instruments show level flight.

The FAA medical certificate for private pilot, recreational, and student pilot privileges. It is valid 60 calendar months if issued before age 40, and 24 calendar months if issued at age 40 or older.

The tendency of the airframe to rotate opposite the propeller's rotation in accordance with Newton's third law. In a typical single it rolls the aircraft left, increasing left tire load on the ground and requiring right rudder/aileron.

The standard rectangular path flown around an airport for landing, consisting of the upwind, crosswind, downwind, base, and final legs. Turns are left-hand unless otherwise specified, typically flown at 1,000 ft AGL.

An avionics device that replies to ATC secondary radar interrogations with a code and, in Mode C/S, pressure altitude. Standard codes include 1200 (VFR), 7500 (hijack), 7600 (lost comms), and 7700 (emergency).

A gyroscopic instrument that shows rate of roll and rate of turn, with an inclinometer (the ball) showing coordination. The wing index aligned with the standard-rate marks indicates a 3-degree-per-second turn.

A system using an engine-driven pump to spin gyroscopic instruments (attitude and heading indicators). A vacuum failure causes these gyros to slowly degrade, which is why glass and partial-panel skills matter.

The maximum speed at which the flaps may be extended to a given setting. It marks the top of the white arc on the airspeed indicator.

Minimum visibility and cloud clearance required for visual flight under 14 CFR 91.155, which vary by airspace class and altitude (e.g., 3 SM and 1,000 ft above / 500 ft below / 2,000 ft horizontal in controlled airspace below 10,000 ft MSL).

A ground-based navigation aid transmitting 360 radials that lets a pilot determine bearing to or from the station regardless of heading. Accuracy is line-of-sight; reception range and class (Terminal, Low, High) depend on altitude and distance.

The maximum speed at which the aircraft may be flown with the landing gear extended and locked. Exceeding it can damage the gear or gear doors.

The maximum speed at which the landing gear may be safely extended or retracted. In some aircraft the extension and retraction limits differ.

For a multiengine airplane, the minimum airspeed at which directional control can be maintained with the critical engine inoperative and the other at takeoff power. It is marked by a red radial line and assumes specific certification conditions.

The maximum speed the aircraft may ever be flown, marked by the red line on the airspeed indicator. Exceeding it risks structural failure or destructive flutter.

The maximum structural cruising speed; the top of the green arc and bottom of the yellow arc. Flight above Vno (in the caution range) is permitted only in smooth air.

The speed at which back pressure is applied to raise the nose and rotate the aircraft into the takeoff attitude during the takeoff roll.

The power-off stalling speed in a specified clean configuration (flaps and gear up). It marks the bottom of the green arc on the airspeed indicator.

The power-off stalling speed in the landing configuration (full flaps, gear down). It marks the bottom of the white arc on the airspeed indicator.

The airspeed that produces the greatest altitude gain per unit of horizontal distance, used to clear obstacles after takeoff. It is slower than Vy and occurs where the difference between thrust available and thrust required is greatest.

The airspeed that produces the greatest altitude gain per unit of time, used for an efficient normal climb. It occurs where excess power is greatest; Vx and Vy converge at the absolute ceiling.

The boundary where warm air overtakes and rides up over retreating cold air, producing widespread low ceilings, steady precipitation, poor visibility, and stratiform clouds over a large area well ahead of the surface front.

The calculation ensuring the aircraft is loaded within its maximum weight and that the center of gravity falls within the approved envelope. Operating outside limits degrades performance, stability, and control.

A network of ground stations and geostationary satellites that corrects GPS signals to improve accuracy and integrity, enabling approaches with vertical guidance (LPV) and lateral precision down to near-Category I minimums.

A sudden change in wind speed and/or direction over a short distance, which can occur at any altitude. It is most hazardous near the ground during takeoff and landing and is associated with thunderstorms, frontal passages, and temperature inversions.