78 aviation and flight-tracking terms explained in plain English, from ADS-B and squawk codes to flight levels, holding patterns and the lights on a plane at night.
- 1090ES
1090ES (1090 MHz Extended Squitter) is the main ADS-B data link, used worldwide. It sends ADS-B messages on the same 1090 MHz frequency used by Mode S transponder replies, as longer "extended" spontaneous transmissions called squitters. Airliners, business jets and any aircraft flying at or above 18,000 ft in the US must use 1090ES. Most community receivers listen on 1090 MHz. See how ADS-B works.
- ADS-B
ADS-B (Automatic Dependent Surveillance-Broadcast) is a surveillance system in which an aircraft determines its own position, usually by GPS, and broadcasts it along with altitude, velocity, identity and status about twice per second. The broadcasts are unencrypted and can be received by air traffic control, other aircraft and ground receivers. ADS-B is the data source behind live flight maps, including our live sky tool. Read more in how ADS-B works.
- ADS-B In
ADS-B In is the receiving side of ADS-B. An aircraft with ADS-B In can display other ADS-B traffic in the cockpit, and in the US it can also receive rebroadcast traffic (TIS-B) and, on 978 MHz, free weather information (FIS-B) from ground stations. ADS-B In is optional for aircraft. A ground-based community feeder is essentially an ADS-B In receiver that shares what it hears.
- ADS-B Out
ADS-B Out is equipment that broadcasts an aircraft's position, altitude, velocity and identity. In the US it has been required since January 1, 2020 in "rule airspace": Class A, B and C airspace, within 30 nm of major Class B airports, above 10,000 ft MSL (except within 2,500 ft of the ground) and some airspace over the Gulf of Mexico. Aircraft without it, such as many gliders and antique aircraft, may not appear on ADS-B maps.
See also: ADS-B, ADS-B In, Class B airspace, Transponder
- AGL (above ground level)
AGL means above ground level: height measured from the ground directly below. Pilots use AGL for things like traffic pattern altitude and minimum heights over obstacles. Flight trackers show altitude relative to sea level instead, so to estimate a plane's height above you, subtract your own elevation. In Denver, at about 5,300 ft, a plane at 7,000 ft MSL is only about 1,700 ft AGL.
See also: MSL (mean sea level), Barometric altitude, Traffic pattern
- Airspeed
Airspeed is how fast an aircraft moves relative to the surrounding air. Pilots fly by indicated airspeed, which drives lift and handling, while true airspeed corrects for thinner air at altitude. Airspeed differs from ground speed by the effect of wind: a jet with a true airspeed of 470 knots and a 100 knot tailwind covers the ground at 570 knots. ADS-B usually reports ground speed, sometimes airspeed too.
See also: Ground speed, Knots, Heading
- ATC (air traffic control)
ATC, air traffic control, is the service that separates aircraft and manages traffic flow. In the US it is provided by the FAA through airport towers, which handle runways and the immediate airport area; TRACONs, which handle arrivals and departures within roughly 30 to 50 nm; and Centers, which handle en route traffic. Controllers assign squawk codes, headings and altitudes.
See also: TRACON, Center (ARTCC), Squawk code
- Barometric altitude
Barometric altitude is altitude worked out from outside air pressure. In ADS-B and transponder replies it is reported as pressure altitude, referenced to the standard 29.92 inHg, usually in 25 ft steps. Because all aircraft in the same airspace measure pressure the same way, it is what air traffic control uses for vertical separation. It can differ from GPS height by hundreds of feet. See what altitude numbers mean.
See also: Pressure altitude, Geometric altitude, Flight level, MSL (mean sea level)
- Beacon (anti-collision light)
The beacon, or red anti-collision light, is a flashing or rotating red light mounted on the top and bottom of the fuselage. Pilots switch it on just before starting engines and leave it on while the engines run, which also warns ground crew to keep clear. Together with white strobes, it is the main way to spot an aircraft at night. See spotting planes at night.
See also: Strobe lights, Navigation lights, Landing lights
- Bearing
Bearing is the direction from one point to another, measured in degrees clockwise from north: 0° is north, 90° east, 180° south and 270° west. Our live sky tool shows the bearing from you to each aircraft, rounded to a compass point such as NE, so you know which way to look. Combined with the elevation angle, it tells you exactly where in the sky to find a plane.
See also: Elevation angle, Heading, Track
- Bizjet (business jet)
A bizjet is a business jet: a jet aircraft typically seating 4 to 19 passengers, used for corporate, charter, fractional ownership or private travel. Examples include the Citation Excel, Phenom 300, Challenger 350 and Gulfstream G650. Many have rear-mounted engines and cruise at 41,000 to 51,000 ft. Bizjets often use N-number callsigns and privacy programs like LADD.
See also: N-number, LADD, PIA (Privacy ICAO Address), Regional jet
- Callsign
A callsign is the identifier an aircraft uses with air traffic control and broadcasts in its ADS-B identification message. Airline flights combine a three-letter ICAO airline code and a flight number (DAL123 is Delta 123). Private aircraft usually use their registration, such as N172SP. Military flights use words plus numbers, such as REACH. See callsigns and flight numbers.
See also: ICAO code, IATA code, Registration, N-number
- Center (ARTCC)
An ARTCC (air route traffic control center), usually just called "Center", controls aircraft en route between terminal areas, mostly at higher altitudes. The continental US is divided among 20 Centers, each covering a large region and split into many sectors. A cruising airliner is handed from sector to sector and Center to Center along its route, then passed to a TRACON as it begins its descent.
See also: ATC (air traffic control), TRACON, Cruise
- Class B airspace
Class B airspace surrounds the busiest airports in the US, typically from the surface up to 10,000 ft MSL, in layers that widen with height like an upside-down wedding cake. Every aircraft inside needs an air traffic control clearance, and ADS-B Out is required in it and within 30 nm of the primary airport (the "Mode C veil"). Examples include the airspace around Atlanta, Chicago O'Hare and Los Angeles.
See also: ADS-B Out, ATC (air traffic control), TRACON
- Climb
A climb is any period when an aircraft is gaining altitude. On a flight map it shows as a positive vertical rate. Airliners typically climb at 1,500 to 3,500 feet per minute after takeoff, slowing as they approach cruise altitude, often 20 to 30 minutes later. Small piston aircraft usually climb at 500 to 1,000 feet per minute.
See also: Vertical rate, Descent, Cruise, SID (standard instrument departure)
- Contrail
A contrail (condensation trail) is a line-shaped cloud of ice crystals that forms when hot, humid engine exhaust meets very cold air, typically around -40 °C and usually above roughly 26,000 ft. In dry air contrails vanish within seconds; in air saturated with respect to ice they persist and can spread into cirrus-like cloud. A contrail is a strong hint that a plane is a jet at cruise. See contrails explained.
See also: Cruise, Flight level
- Cruise
Cruise is the en route phase of flight, after the climb and before the descent, usually flown at a steady altitude. Airliners typically cruise at 30,000 to 41,000 ft at around 450 to 500 knots true airspeed; business jets often go higher. On long flights aircraft may "step climb" to higher levels as they burn fuel and become lighter.
See also: Climb, Descent, Flight level, Airspeed
- Descent
A descent is any period when an aircraft is losing altitude, shown as a negative vertical rate. Airliners usually start descending 100 to 150 nm from their destination, often following a STAR, at 1,000 to 3,000 feet per minute. On final approach the rate drops to about 700 to 800 feet per minute.
See also: Vertical rate, Climb, STAR (standard terminal arrival), Final approach
- Elevation angle
The elevation angle is the angle between the horizon and a line from you to an object in the sky. The horizon is 0° and straight overhead is 90°. Our live sky tool calculates it from the aircraft's height above you and its distance, so you can see "35° up". At arm's length, a fist covers about 10°. See how far away is that plane?
See also: Bearing, AGL (above ground level), Nautical mile
- Emitter category
The emitter category is a code in each ADS-B identification message describing the type of aircraft. Common values: A1 light (under 15,500 lb), A2 small (15,500 to 75,000 lb), A3 large (75,000 to 300,000 lb), A4 high-vortex large (such as the 757), A5 heavy (over 300,000 lb), A6 high performance and A7 rotorcraft. B categories cover gliders, balloons, ultralights and drones.
See also: Heavy, Rotorcraft, ADS-B
- ETA (estimated time of arrival)
ETA stands for estimated time of arrival: the predicted time an aircraft will reach its destination or a point along its route. Airlines and air traffic control update ETAs continually as winds, routing and delays change. Passengers usually see the time the aircraft reaches the gate, while ATC cares about the time it reaches the runway, so the two can differ by several minutes.
See also: Ground speed, Holding pattern
- Feeder
A feeder is a receiver, often run by a volunteer, that picks up aircraft broadcasts and forwards them to a tracking network over the internet. A typical feeder is a small antenna, a USB software-defined radio and a single-board computer. Our data comes from airplanes.live, a community network of feeders. More feeders mean better coverage, especially of low aircraft, and timing-synchronised feeders enable MLAT.
See also: ADS-B In, MLAT (multilateration), 1090ES
- Final approach
Final approach is the last part of an approach, when the aircraft is lined up with the runway and descending to land. Airliners usually establish on final 5 to 15 nm from the runway, following a 3° glideslope that loses about 300 ft per nautical mile, so they are around 3,000 ft above the airport at 10 nm. Typical jet approach speeds are 130 to 150 knots.
See also: Glideslope, ILS (instrument landing system), Go-around, Runway heading
- Flight level
A flight level is a pressure altitude expressed in hundreds of feet, with the altimeter set to the standard 29.92 inHg (1013.25 hPa). FL350 means 35,000 ft of pressure altitude. In the US and Canada, flight levels are used at and above 18,000 ft (FL180). Elsewhere the transition altitude varies. Using a common reference keeps aircraft separated regardless of local weather.
See also: Pressure altitude, Transition altitude, Barometric altitude, RVSM
- Geometric altitude
Geometric altitude is an aircraft's height determined by satellite navigation, usually GPS, typically referenced to the WGS-84 ellipsoid. ADS-B messages often include it alongside barometric altitude. The two can differ by hundreds of feet depending on air pressure and temperature. Aviation separation still uses barometric altitude, so that is the main number on flight maps.
See also: Barometric altitude, Pressure altitude, MSL (mean sea level)
- Glideslope
A glideslope (or glide path) is the descent path that guides an aircraft down to the runway. The usual angle is 3°, which works out to about 300 ft of descent per nautical mile, or a descent rate of roughly five times the ground speed in feet per minute. On an ILS it is provided by a radio transmitter beside the runway; satellite approaches provide a similar path.
See also: ILS (instrument landing system), Final approach, Descent
- Go-around
A go-around is when a pilot discontinues an approach or landing and climbs away, usually to fly around and approach again. Reasons include an aircraft still on the runway, an unstable approach, gusty wind or poor visibility. It is a normal, trained procedure, not an emergency. On a map, a go-around shows as a climb from low altitude near the runway, followed by a loop back to final.
See also: Final approach, Traffic pattern, Runway heading
- Ground speed
Ground speed is how fast an aircraft moves over the surface of the Earth, usually in knots. It equals airspeed plus or minus the wind component. ADS-B reports ground speed, which is why an eastbound jet in a strong jet stream can show 600 knots or more while a westbound one shows 400. Below 10,000 ft MSL in the US, aircraft are generally limited to 250 knots indicated airspeed.
- Heading
Heading is the direction the aircraft's nose points, in degrees from north. It is not always the direction the aircraft actually moves over the ground: in a crosswind, the aircraft points slightly into the wind and its track differs from its heading. Air traffic control often assigns headings, as in "turn left heading 270". Most flight maps show track, because that is what ADS-B always reports.
See also: Track, Bearing, Runway heading
- Heavy
Heavy is added to the radio callsign of aircraft whose maximum takeoff weight is 300,000 lb or more, such as the 777, 787 and A330: "Delta 46 heavy". It warns controllers and pilots of strong wake turbulence so they leave extra spacing. The A380 uses "super". The suffix is spoken only; it is not part of the ADS-B callsign, but these aircraft usually broadcast emitter category A5.
See also: Widebody, Emitter category, Callsign
- Holding pattern
A holding pattern is an oval racetrack flown over a fixed point while an aircraft waits, usually for weather or traffic at its destination. Inbound legs last 1 minute at or below 14,000 ft MSL and 1.5 minutes above, with standard rate turns at each end, normally to the right. Aircraft stack 1,000 ft apart and leave from the bottom. See why planes circle.
See also: Standard rate turn, STAR (standard terminal arrival), ATC (air traffic control)
- IATA code
IATA codes are identifiers assigned by the International Air Transport Association. Airlines get two-character codes, such as AA, DL, UA and WN (Southwest), used in flight numbers on tickets. Airports get three-letter codes, such as LAX, ORD and JFK, used on bag tags and departure boards. Air traffic control and ADS-B callsigns use the longer ICAO codes instead.
- ICAO code
ICAO codes are identifiers assigned by the International Civil Aviation Organization. Airlines get three-letter codes, such as AAL, DAL, UAL and SWA, which appear in ADS-B callsigns. Airports get four-letter codes; in the contiguous US these usually add a K to the IATA code, so LAX becomes KLAX. ICAO also assigns aircraft type designators and the 24-bit aircraft addresses.
See also: IATA code, Callsign, ICAO type designator, ICAO hex address
- ICAO hex address
The ICAO hex address (24-bit aircraft address, or Mode S code) is a unique identifier programmed into an aircraft's transponder, usually written as six hexadecimal characters such as A1B2C3. Every Mode S and ADS-B message includes it, so trackers use it to link messages and look up the aircraft's type and registration. US-registered aircraft have addresses beginning with A; US military aircraft often begin with AE.
See also: Mode S, Registration, PIA (Privacy ICAO Address), Transponder
- ICAO type designator
An ICAO type designator is a code of two to four characters that identifies an aircraft model in flight plans and air traffic systems. Examples: B738 for the Boeing 737-800, A20N for the A320neo, C172 for the Cessna 172, H60 for the Black Hawk. Flight maps show these codes; our aircraft pages explain what each looks like.
See also: ICAO code, ICAO hex address, Registration
- IFR (instrument flight rules)
IFR, instrument flight rules, are the rules for flying with reference to instruments, on a filed flight plan, under air traffic control clearance. IFR flights can fly in cloud and are separated from other IFR traffic by controllers. All scheduled airline flights operate IFR, and in the US all aircraft at or above 18,000 ft must. The alternative is VFR.
See also: VFR (visual flight rules), ATC (air traffic control), SID (standard instrument departure), STAR (standard terminal arrival)
- ILS (instrument landing system)
An ILS, instrument landing system, is a ground-based radio system that guides aircraft on final approach. A localizer gives left-right guidance to the runway centreline and a glideslope gives vertical guidance, usually at 3°. With suitable equipment and crew training, some ILS approaches allow landings in very low visibility. On a map, ILS arrivals line up on the extended runway centreline many miles out.
See also: Glideslope, Final approach, Runway heading
- Knots
A knot is one nautical mile per hour, about 1.15 mph or 1.852 km/h. Aviation uses knots for airspeed, ground speed and wind. Rough conversions: 100 knots is about 115 mph; 250 knots, the usual US speed limit below 10,000 ft, is about 288 mph; 480 knots, a typical airliner cruise ground speed, is about 550 mph.
See also: Nautical mile, Ground speed, Airspeed
- LADD
LADD (Limiting Aircraft Data Displayed) is an FAA program that lets US aircraft owners ask that their aircraft be hidden or limited in flight data the FAA provides to tracking companies. It applies to FAA-sourced data, not to the radio broadcast itself, so community networks built on their own receivers may still show LADD aircraft; each site sets its own policy. Often paired with PIA.
See also: PIA (Privacy ICAO Address), ICAO hex address, Bizjet (business jet)
- Landing lights
Landing lights are powerful white lights that point forward from the wings, nose gear or fuselage. Pilots use them for takeoff and landing, and many also switch them on below 10,000 ft so other pilots can see them. An aircraft approaching you with landing lights on can appear as a single bright, almost stationary light, a common source of "hovering light" reports near airports.
See also: Navigation lights, Beacon (anti-collision light), Strobe lights, Final approach
- METAR
A METAR is a routine aviation weather observation for an airport, usually issued hourly and more often when weather changes quickly. It reports wind, visibility, weather, clouds, temperature, dew point and altimeter setting in a compact code, for example "KORD 111651Z 27012KT 10SM FEW050 18/07 A3002". The wind in a METAR tells you which way an airport is likely landing, since aircraft land into the wind.
See also: PIREP, NOTAM, Runway heading
- MLAT (multilateration)
MLAT, multilateration, calculates an aircraft's position from tiny differences in the time its transponder signals arrive at several receivers with synchronised clocks. It needs at least four receivers hearing the same signal. It lets networks locate aircraft that have a Mode S transponder but do not broadcast ADS-B position. MLAT positions are less precise and update less often than ADS-B, and only work where coverage is dense.
- Mode C
Mode C is a transponder mode that replies to radar interrogations with the aircraft's squawk code and its pressure altitude in 100 ft steps. Mode C transponders do not send a unique aircraft address, so community networks generally cannot identify or locate them. "Mode C veil" refers to the 30 nm area around major Class B airports where altitude-reporting transponders and ADS-B are required.
See also: Mode S, Transponder, Squawk code, Class B airspace
- Mode S
Mode S ("select") is a transponder standard in which each aircraft has a unique 24-bit ICAO address, so radar can interrogate aircraft individually. Mode S replies include altitude and squawk, and enhanced versions share more data. 1090ES ADS-B is an extension of Mode S. Aircraft with Mode S but no ADS-B position can still be located by MLAT.
See also: Mode C, 1090ES, ICAO hex address, MLAT (multilateration)
- MSL (mean sea level)
MSL, mean sea level, is the reference for most aviation altitudes. Charts, air traffic control and flight trackers express altitudes relative to sea level, not the ground below. A plane at 3,000 ft MSL over the coast is 3,000 ft up; over a city at 1,000 ft elevation it is only 2,000 ft above the ground (AGL). Trackers show pressure altitude, which approximates MSL.
See also: AGL (above ground level), Barometric altitude, Pressure altitude
- N-number
An N-number is the registration of a US civil aircraft. It starts with N followed by up to five characters: digits and, at the end, up to two letters, such as N123AB or N7. Private aircraft usually use it as their callsign. Each N-number maps to a specific 24-bit ICAO address beginning with A, and is listed in the FAA's public registry.
See also: Registration, Callsign, ICAO hex address, PIA (Privacy ICAO Address)
- Narrowbody
A narrowbody is an airliner with a single aisle, typically seating 100 to 240 passengers. It is the most common airliner over US cities. Examples include the 737-800, 737 MAX 8, A320, A321, A220-300 and 757. Most use two engines under the wings and fly domestic and short international routes.
See also: Widebody, Regional jet, Emitter category
- Nautical mile
A nautical mile (nm) is exactly 1.852 km, about 1.15 statute miles or 6,076 ft. It was originally based on one minute of latitude, which makes it convenient for navigation. Aviation uses nautical miles for distances and knots (nautical miles per hour) for speed. A 3° glideslope descends about 300 ft per nautical mile.
See also: Knots, Elevation angle, Glideslope
Navigation lights (position lights) are steady lights that show an aircraft's orientation at night: red on the left wingtip, green on the right wingtip and white at the tail. If you see red on the left and green on the right, the aircraft is coming toward you. They are used with the red beacon and white strobes. See spotting planes at night.
See also: Beacon (anti-collision light), Strobe lights, Landing lights
- NOTAM
A NOTAM (Notice to Air Missions, formerly Notice to Airmen) is an official notice about something that affects flight operations, usually temporarily: a closed runway, an unlit tower, an airshow, parachute jumping, or a TFR. Pilots must review relevant NOTAMs before a flight. NOTAMs explain many unusual patterns on the map, such as aircraft avoiding an area around a stadium or VIP visit.
See also: TFR (temporary flight restriction), METAR, PIREP
- PIA (Privacy ICAO Address)
PIA (Privacy ICAO Address) is an FAA program that lets eligible US aircraft owners use a temporary 24-bit ICAO address that is not linked to the aircraft's registration in public records, often together with a third-party callsign. The aircraft still broadcasts ADS-B and still appears on maps, but its type and owner may show as unknown. It is commonly used alongside LADD.
See also: LADD, ICAO hex address, Registration
- PIREP
A PIREP is a pilot report of weather encountered in flight: turbulence, icing, cloud tops, wind shear or visibility. Pilots pass them to air traffic control, and they are shared with other pilots and forecasters. PIREPs fill gaps between ground observations like METARs, and they help explain why aircraft sometimes change altitude together to escape a bumpy layer.
See also: METAR, NOTAM, ATC (air traffic control)
- Piston aircraft
A piston aircraft uses one or more reciprocating engines, similar in principle to a car engine, to drive propellers. Most training and private aircraft are pistons, including the Cessna 172, Piper PA-28 and Cirrus SR22. They usually fly below 12,000 ft at 90 to 180 knots and have a distinctive buzzing sound. The Robinson R44 is a piston helicopter.
See also: Turboprop, VFR (visual flight rules), Traffic pattern
- Positioning flight
A positioning flight (also ferry or repositioning flight) moves an aircraft without paying passengers or cargo, for example to start the next day's schedule at another airport, to reach a maintenance base, or after a delivery from the manufacturer. Positioning flights may use a different flight number from normal service or a registration-style callsign, which can make an airliner look out of place on the map.
- Pressure altitude
Pressure altitude is the altitude an altimeter reads when set to the standard pressure of 29.92 inHg (1013.25 hPa). Transponders and ADS-B report it regardless of the pilot's altimeter setting, and air traffic control corrects it for local pressure at lower altitudes. Above the transition altitude, it is used directly as a flight level. Roughly 1 inHg of pressure difference equals about 1,000 ft.
See also: Barometric altitude, Flight level, Transition altitude
- Red-eye
A red-eye is an overnight passenger flight that departs late in the evening and arrives early the next morning, named for how passengers' eyes look after little sleep. In the US, typical red-eyes run from the West Coast or Hawaii to the East Coast. Late-night jets over your house are often red-eyes or cargo flights, such as FedEx and UPS operations.
See also: Positioning flight, ETA (estimated time of arrival)
- Regional jet
A regional jet is a smaller jet airliner, typically 50 to 100 seats, used on shorter routes and to feed hubs. Common types include the Embraer E175, CRJ700 and CRJ900. In the US most are operated by regional carriers such as SkyWest, Republic and Envoy under brand names like United Express or American Eagle, using their own callsigns.
See also: Narrowbody, Turboprop, Callsign
- Registration
An aircraft's registration (tail number) is its national identity, painted on the fuselage or tail. The prefix shows the country: N for the US, C for Canada, G for the UK, D for Germany, JA for Japan. Registrations stay with the airframe and are linked in public registries to the ICAO hex address broadcast by its transponder. Private flights often use the registration as their callsign.
See also: N-number, ICAO hex address, Callsign
- Rotorcraft
A rotorcraft is an aircraft that gets lift from rotating blades rather than fixed wings. Helicopters are by far the most common; gyroplanes are another type. ADS-B labels rotorcraft as emitter category A7. Examples include the H125/AS350, H135, R44 and UH-60. See why helicopters circle.
See also: Emitter category, AGL (above ground level)
- Runway heading
Runway heading is the magnetic direction a runway points. Runway numbers are this direction divided by ten and rounded: runway 27 points about 270°, west. The opposite end is runway 9. Parallel runways add L, C or R. Because aircraft take off and land into the wind, the runway direction in use changes with wind and decides which neighbourhoods hear arrivals or departures.
See also: Heading, Final approach, METAR
- RVSM
RVSM (Reduced Vertical Separation Minimum) allows aircraft to be separated vertically by 1,000 ft instead of 2,000 ft between FL290 and FL410, doubling the number of usable cruising levels. Aircraft and crews must be specially approved and use highly accurate altimetry. RVSM is why you can see two airliners crossing paths one above the other only 1,000 ft apart at cruise.
See also: Flight level, Cruise, Pressure altitude
- SID (standard instrument departure)
A SID, standard instrument departure, is a published route that takes aircraft from a runway to the en route system, with set turns, waypoints and often altitude and speed limits. SIDs simplify clearances and keep departures clear of arrivals and terrain. Satellite-based SIDs produce precise, repeatable tracks, which can concentrate departures over the same neighbourhoods. The arrival equivalent is a STAR.
See also: STAR (standard terminal arrival), Climb, IFR (instrument flight rules)
- Squawk code
A squawk code is a four-digit code (each digit 0 to 7) set on an aircraft's transponder so air traffic control can identify it on radar. Most are assigned per flight. Special codes include 1200 (VFR in the US), 7500 (unlawful interference), 7600 (radio failure) and 7700 (general emergency). See squawk codes explained.
See also: Transponder, Mode C, ATC (air traffic control)
- Standard rate turn
A standard rate turn is a turn at 3° per second, so a full 360° takes two minutes and a 180° turn takes one. Instrument procedures, including holding patterns, are built around it. The bank angle needed rises with speed; a rough rule is 10 percent of the true airspeed plus 7, so about 19° at 120 knots. Faster aircraft usually limit bank to about 25°.
See also: Holding pattern, Heading
- STAR (standard terminal arrival)
A STAR, standard terminal arrival route, is a published path that brings arriving aircraft from the en route system toward an airport, often with altitude and speed restrictions. STARs connect to approach procedures for the runway in use. Several STARs usually feed a big airport from different directions, which is why arrival traffic converges along predictable lines. The departure equivalent is a SID.
See also: SID (standard instrument departure), Descent, Holding pattern, TRACON
- Strobe lights
Strobe lights are very bright white flashing lights, usually on the wingtips and often the tail. Pilots turn them on when entering the runway and keep them on in flight, making the aircraft visible from many miles away at night. Airliners commonly flash in a double pattern. Together with the red beacon, strobes distinguish aircraft from satellites, which never blink.
See also: Beacon (anti-collision light), Navigation lights, Landing lights
- TFR (temporary flight restriction)
A TFR, temporary flight restriction, is an area where flight is limited for a set time, announced by NOTAM. Common TFRs cover wildfires, disaster areas, major sporting events, space launches and VIP movements such as presidential visits. Some ban most aircraft entirely; others allow only certain flights. TFRs explain why the sky over an event can suddenly empty of small aircraft.
See also: NOTAM, ATC (air traffic control)
- Track
Track is the direction an aircraft is actually moving over the ground, in degrees from north. It is what ADS-B reports and what the arrow on a flight map shows. Track can differ from heading because of wind drift. In our live sky tool, track tells you which way the plane is crossing your sky, which helps when two aircraft are in the same direction from you.
See also: Heading, Bearing, Ground speed
- TRACON
A TRACON (terminal radar approach control) is a US air traffic facility that handles aircraft arriving at and departing from airports in its area, typically within about 30 to 50 nm and up to around 10,000 to 17,000 ft. TRACON controllers sequence arrivals onto final approach, issue headings and altitudes, and hand departures to the Center. Large metro areas often have one TRACON covering several airports.
See also: ATC (air traffic control), Center (ARTCC), Class B airspace
- Traffic pattern
A traffic pattern (circuit) is a rectangular path around a runway used to organise arrivals and practice landings. It has upwind, crosswind, downwind, base and final legs. Piston aircraft typically fly it at about 1,000 ft above ground, and turns are to the left unless published otherwise. Student pilots fly repeated patterns, which is why small planes seem to circle small airports for an hour.
See also: AGL (above ground level), Final approach, Go-around, Piston aircraft
- Transition altitude
The transition altitude is the altitude at or below which aircraft use the local altimeter setting, and above which they set 29.92 inHg (1013.25 hPa) and fly flight levels. In the US and Canada it is 18,000 ft. Elsewhere it varies by country and airport, often between 3,000 and 7,000 ft, though some are higher. Descending aircraft switch back at the transition level.
See also: Flight level, Pressure altitude, Barometric altitude
- Transponder
A transponder is an aircraft radio that automatically replies when interrogated by secondary radar, sending the squawk code and, depending on its mode, altitude and a unique address. Mode C units send code and altitude; Mode S units add an address and more data. Many modern Mode S transponders also broadcast 1090ES ADS-B.
See also: Squawk code, Mode C, Mode S, ADS-B Out
- Turboprop
A turboprop uses a gas turbine engine to drive a propeller. Turboprops are efficient at medium speeds and altitudes, typically 250 to 300 knots at 15,000 to 28,000 ft, and work well from short runways. Examples include the ATR 72, Cessna Caravan, Pilatus PC-12, King Air and military C-130. They have a characteristic whining drone.
See also: Piston aircraft, Regional jet
- UAT
UAT (Universal Access Transceiver) is an ADS-B data link on 978 MHz used only in the United States, and only by aircraft flying below 18,000 ft. It is popular with general aviation because UAT receivers also get free weather (FIS-B) and traffic information from ground stations. Receivers must listen on 978 MHz to hear UAT aircraft; a 1090 MHz-only receiver will miss them.
- Vertical rate
Vertical rate (vertical speed) is how fast an aircraft's altitude is changing, in feet per minute. Positive values mean a climb, negative a descent. Typical figures: 1,500 to 3,500 fpm for an airliner climbing after takeoff, 1,000 to 3,000 fpm descending from cruise, about 700 to 800 fpm on final approach, and close to zero in level flight.
See also: Climb, Descent, Final approach
- VFR (visual flight rules)
VFR, visual flight rules, let pilots fly by looking outside, responsible for seeing and avoiding other aircraft, in weather with minimum visibility and distance from clouds. Many small private and training flights are VFR, often without talking to air traffic control. In the US, VFR aircraft not receiving ATC services squawk 1200, and above 3,000 ft AGL they cruise at thousands plus 500 ft, such as 5,500.
See also: IFR (instrument flight rules), Squawk code, Piston aircraft
- Widebody
A widebody is an airliner with two aisles, typically seating about 250 to 400 or more passengers and flying long routes. Examples include the 767, 777-300ER, 787-9, A330-300, A350-900 and 747-8. Most are "heavy" on the radio and broadcast emitter category A5.
See also: Narrowbody, Heavy, Emitter category
- Winglet
A winglet is a near-vertical extension at the tip of a wing. It reduces the wingtip vortex, cutting drag and fuel burn, typically by a few percent on long flights. Shapes vary and help with identification: blended winglets on many 737-800s, split-scimitar winglets on others, the split "AT" tips on the 737 MAX, and "sharklets" on the A320neo family.
See also: Narrowbody, Widebody