Aviation glossary & flight tracking terminology
We've put together a glossary of terms which you may encounter either on our site or in aviation in general that we hope enriches your flight tracking experience. The Aviation industry uses many complex acronyms, jargon and terminology which this glossary will help you unravel. The vocabulary we look at centers around flight tracking, characteristics of flight, flight tracking technology/communication and general aviation terminology.
Automatic Dependent Surveillance-Broadcast is the main technology we use to track aircraft. Automatic: data is sent from the aircraft without pilot intervention; Dependent: it is dependent on the aircraft's navigation system for position information. An aircraft that has a transponder that is ADS-B equipped enables extensive flight details to be sent such as altitude, ground speed, call sign to be transmitted. In some cases additional information, like airspeed, wind, and temperature are sent as well. With our global network of ADS-B receivers we are able to use these transmissions to provide a unique flight tracking service.
You can read more about ADS-B here.
The aircraft's age listed on Flightradar24 is from the first flight. Delivery of the aircraft to the operator usually occurs within weeks of the first flight. The age of commercial airliners varies greatly, and largely depends on the number of pressurisation cycles. A Boeing 747-400 for example was designed to have a 20 year lifespan. Read more about aircraft age here.
An aircraft livery is the paint scheme which is applied. Airlines often create special liveries in support of events, anniversaries, or advertising campaigns. A recent example of this is the Qantas 100th anniversary livery applied to 787-9 VH-ZNJ.
Each kind of aircraft is assigned an aircraft type, which is a standardized name for the aircraft. Type codes are assigned by ICAO and consist of two to four letters and numbers. These type codes are often used when filing flight plans. We use these type codes on Flightradar24 for filtering aircraft.
Airways are predefined routes which connect set locations through the use of navaids and waypoints.
For each flight tracked on Flightradar24 the calibrated altitude reported from the aircraft, which is a pressure-derived value, is displayed. Extended Mode S Data received from some aircraft also includes the GPS-derived altitude of the aircraft.
Air traffic control (ATC)
Air traffic controllers are responsible for the safe coordination of flights from pushback to arrival. They are a ground based service whose primary objective is to safely facilitate the movement of air traffic, prevent aircraft collisions, as well as providing any other information a pilot may require. Find out more about air traffic controllers here.
Area Navigation (RNAV)
Area Navigation (RNAV) is a form of IFR navigation where an aircraft can fly a route between a network of radio beacons, instead of having to fly from one beacon to the next.
Auxiliary power unit (APU)
An aircraft auxiliary power unit (APU) is a device that provides energy in order to power electrical systems. Most APUs are simply small jet engines which take fuel directly from the aircraft's main fuel tanks. In normal operations an APU will be started prior to main engine start, shut down during flight, and then restarted after the main engines are shut down again.
Automatic Direction Finding (ADF)
An ADF is a radio navigation instrument which provides the relative bearing from an aircraft to a radio station, usually an NDB.
Automatic Terminal Information Service (ATIS)
The Automatic Terminal Information Service (ATIS) is a continuous, recorded broadcast, which provides information such as weather, active runway, runway state, NOTAMs and any other information that may be needed by Pilots. Typically a broadcast is coded with a reference 'Information' letter (Information Alpha) signifying the current version of an ATIS. Air traffic controllers will inform approaching aircraft of the current ATIS ('Information November is current') to ensure pilots have the information they need to carry out a safe landing.
Audio Control Panel (ACP)
An aircraft’s Audio Control Panel is often found on the pedestal section of an aircraft and allows Pilots to select which audio sources they want to hear, and transmit on. Read about a recent incident involving the ACP onboard a flight.
Taken together, the CVR (Cockpit Voice Recorder) and FDR (Flight Data Recorders) are informally known as the black boxes, though in fact, most are bright orange. Both recorders are designed to survive a crash and are equipped with beacons to assist investigators in locating them quickly after an aircraft accident. Read more about black boxes here.
Civil Aviation Authority (CAA)
Founded in 1972, the CAA regulates all aspects of civil aviation within the United Kingdom.
Civil Aviation Administration of China
The Civil Aviation Administration of China, is the aviation authority for the People's Republic of China and is based in Beijing, China. Read more about the CAAC here.
Call signs are used by Air Traffic Control to denote a specific flight. These can differ from flight numbers in two respects. Some airline radio call signs are different from the airline's name, either for reasons of history or for easy understanding over the radio. Additionally, in recent years, flights have begun using alphanumeric call signs in order to avoid call sign confusion. For example, flight number British Airways 123 would use the call sign Speedbird 1PW, where "Speedbird" is the radio call sign and 1PW is the alphanumeric call sign. This helps avoid confusion over the radio, where two British Airways flights with similar numbers may be talking to the same air traffic controller.
Calibrated airspeed (CAS)
Calibrated airspeed is the airspeed corrected for position and instrument error and is equal to True Airspeed (TAS) at sea level. 'KCAS' is a further abbreviation of Calibrated Airspeed which denotes CAS measured in knots. In some countries the term 'reflected airspeed' is used instead of calibrated airspeed.
Calibrated altitude values reflect the aircraft's altitude above Mean Sea Level, a constant value used in aviation and other applications. 0 feet/meters above Mean Sea Level does not necessarily reflect an aircraft's altitude above the ground.
A climb is a period of flight where an aircraft's altitude increases. Typically a climb occurs immediately after takeoff. It's common to see commercial airliners perform an additional climb enroute, known as a 'Step climb', and this can often be clearly seen in our flight profile graphs.
Cockpit voice recorder (CVR)
The cockpit voice recorder records audio from the flight deck. Usually this is done by recording the sound transmitted through flight crew headsets and also by using microphones placed around the cockpit itself. CVRs help investigators understand what took place on the flight deck during an accident or incident. Find out more here about cockpit voice recorders and how they work.
A codeshare flight is where an agreement exists between two or more airlines who offer the same flight to customers, using their own airline designator.
Coordinated Universal Time (UTC)
UTC is the time standard used in aviation. It is the same as Greenwich Mean Time (GMT) and is regularly used in offsets such as UTC-1 and UTC+1. Find out more about UTC here.
A cost index is a figure, usually between 0-100, which is entered into an aircraft's Flight Management System (FMS) as a way of meeting aircraft operational requirements. The figure that is used is derived from calculating fuel vs time-related costs. An optimized cost index finds the proper balance between the cost of fuel and the cost of time.
De-icing is the process of removing build ups of snow, ice or frost for an aircraft. This is normally done by spraying de-icing fluid, or by applying heat. Take a closer look at de-icing in our blog post here.
A delivery flight is when an aircraft makes its first flight from where it was manufactured, to the airport/airfield chosen by the new operator. Aircraft are usually delivered to an airline’s major hub, though some are flown to special locations for additional modifications like interior configuration or WiFi installation. Read about the delivery flight of the first Bombardier C Series CS100 (now Airbus A220).
A descent is a period of flight where an aircraft's altitude decreases. 'Top of descent' is the point where an aircraft will typically begin descending towards its destination. In an emergency situation such as a rapid decompression an aircraft will perform an emergency descent to below 10,000ft where the oxygen levels in the air are able to ensure passengers and crew may breath unassisted by supplemental oxygen.
European Union Aviation Safety Agency (EASA)
Established in 2002, EASA is a European Union agency tasked with civil aviation safety and regulation.
Equal time point (ETP)
An equal time point is a position on a route where the time taken to return to the departure point, is the same as the time required to reach the arrival point. Head or tailwinds can affect where this precise point along a route may be.
For flights that are no longer in our coverage area, we may estimate their position for up to 240 minutes. These flight tracks are shown as black dashed lines. Read more about estimated positions on Flightradar24.
Eurocontrol is the The European Organisation for the Safety of Air Navigation based in Brussels, Belgium. It is the umbrella organization of national air navigation service providers in Europe.
Extended Mode S
Extended Mode S data is received directly from the aircraft and decoded for display on Flightradar24. Extended Mode S data can include additional information about the speed and altitude of the aircraft as well as weather information, such as wind and outside air temperature.
Ferry flights usually involve flying aircraft to new customers, moving between airports/airfields or positioning aircraft for maintenance.
Federal Aviation Administration (FAA)
Founded in 1958, the FAA is the governing body charged with regulating all areas of civil aviation within the United States.
Flight data recorder (FDR)
Flight Data Recorders record a variety of flight parameters on a constant basis and are used as a forensic tool in the event of a crash or other serious incident. The International Civil Aviation Organization (ICAO) have stringent requirements for the survivability of both the Flight Data Recorder (FDR) and a Cockpit Voice Recorder (CVR). Find out more about a Flight Data Recorders here.
FLARM (a portmanteau of 'flight' and 'alarm') is similar to ADS-B, but used in light aircraft, such as helicopters and gliders. The installation of FLARM equipment is approved by EASA (European Aviation Safety Agency). FLARM compared to traditional transponders has a much lower power consumption making it ideal for the likes of gliders.
Flight Information Region (FIR) / Upper Information Region (UIR)
Flight Information Regions and Upper Information Regions are geographic areas of air traffic control responsibility. The size of a FIRs and UIRs varies and is typically decided by the country, or countries, that the region covers. Oceanic airspace has its own classification as an Oceanic Information Region.
Flight level (FL)
A Flight Level is an aircraft's altitude at standard air pressure, 1013.25 hPa (29.92 inHg), and is expressed in hundreds of feet e.g. 37,000ft is expressed as FL370. Pilots use Flight Levels so that vertical separation can be carried out safely.
A number assigned in the airline's schedule to denote a particular flight or flights. Airlines will regularly use flight number conventions such as designating northbound and eastbound flights with an even number, and southbound and westbound flights with an odd number. Often airlines use larger flight numbers such as BA9171 to indicate a maintenance or positioning flight.
The exact routing a flight will take filed with air traffic control authorities, including specific waypoints the flight will pass over. A flight plan will typically be filed prior a flight by either a pilot or dispatcher. Flight plans are usually filed for IFR flights, with VFR flights only requiring a flight plan if they intend to cross an international border.
Fuel jettison / fuel dumping
Some aircraft are equipped with systems to jettison fuel in the event of an inflight emergency. Fuel jettison or dumping is usually done to decrease the weight of the aircraft so that it may land under its listed Maximum Landing Weight (MLW). Landing above the maximum landing weight is possible, but raises the risk of an issue on landing like burst tires or possible structural damage to the aircraft. Read more about fuel dumping here.
Fuel tankering is when an aircraft carries more fuel that is required for a particular flight, often an amount that is enough to complete the return flight with the required reserves. This is done for a number of operational reasons including fuel costs at the outstation airport, fuel quality, or to simply avoid having to refuel.
When a landing approach cannot be completed safely for any reason, an aircraft will initiate a go-around, which generally includes climbing to a pre-specified altitude and holding point while awaiting further instructions from air traffic control. There are various reasons for why a go-around may occur such as an aircraft ahead slow to vacate the runway or simply an unstable approach. Read more about how go arounds help keep flights safe.
GPS altitude values are based on an ellipsoid of the entire earth, but are also not necessarily indicative of height above the ground.
Ground Proximity Warning System (GPWS)
The Ground Proximity Warning System is designed to alert pilots to the immediate dangers of flight into terrain. Read more about GPWS here.
Ground speed is the speed of the aircraft over the ground; often measured in Knots (nautical miles per hour). If an aircraft is subjected to a headwind this would have a negative impact on the ground speed, whilst a tailwind would have a positive impact.
A ‘grounding’ is when an aircraft requires modifications or repairs in order to be fully compliant with airworthiness regulations. A recent example of this was with the worldwide grounding of the Boeing 737 MAX.
A holding pattern typically occurs during a STAR (see STAR). These are often flown as ovals but sometimes a circular ‘orbit’ is used as a faster substitute. Holding patterns tend to occur over a fixed waypoint, usually a VOR.
Indicated Airspeed is the air speed taken directly from the airspeed indicator without any corrections for temperature or pressure. Airspeed is displayed in knots which can be abbreviated further to KIAS (Knots Indicated Airspeed). IAS is sourced from the pitot tube system usually found around the nose of an aircraft.
The International Air Transport Association is a trade organization made up of the world's airlines and has influence over the commercial aspects of flight. For flight tracking purposes, the two most important pieces of information are IATA airline and airport codes, which are two and three letters long, respectively, and differ from ICAO codes.
List of IATA airline codes
List of IATA airport codes
ICAO 24-bit Address (Hex Code)
Mode S transponders are assigned a unique 24-bit address, often called a hex code because of how it is generally displayed. Once registered the HEX code of an aircraft features on its certificate of registration and is rarely changed.
International Civil Aviation Organization is the arm of the United Nations responsible for international air navigation. ICAO performs a number of essential functions, including assigning aircraft type codes, airline codes, and airport codes. ICAO airline codes consist of three letters (Qantas = QFA) ICAO airport codes consist of four letters (Hong Kong = VHHH). These codes differ from IATA codes.
List of ICAO airline codes
List of ICAO airport codes
List of ICAO aircraft type codes
Instrument flight rules (IFR)
Instrument Flight Rules are a set of regulations used for flying aircraft by instruments alone. An IFR flight may occur when the weather is below visual meteorological conditions (VMC) and is therefore deemed to be instrument meteorological conditions (IMC).
Instrument landing system (ILS)
An ILS allows pilots to conduct instrument approaches by providing precision lateral and vertical guidance.
Integrated Standby Flight Display (IFSD)
The IFSD is a flight instrument, commonly found in modern airliners, which serves as a backup for primary instruments such as the altimeter, airspeed and attitude indicators.
Jetway / Air bridge
A jetway or air bridge is a movable and extendable structure that can be positioned to align with an aircraft door. It can then provide passenger and crew access to and from an airport terminal building.
A Mach number is the ratio of True airspeed to the speed of sound at the altitude of a given flight. If an aircraft were to fly a Mach 0.75 it would be flying at 75% of the speed of sound. Mach ranges can be broken down into Subsonic, Transonic, Supersonic, Hypersonic, High-hypersonic, and re-entry speeds. As of now, all commercial flights are subsonic.
Maneuvering Characteristics Augmentation System (MCAS)
MCAS is a flight control system found on the Boeing 737 MAX. It was introduced to the 737 MAX to modify the pitch behavior of the Boeing 737 NG, providing NG rated pilots with flight characteristic familiarity.
Manufacturer's serial number (MSN)
A Manufacturer's serial number, or MSN, is a unique code assigned to an aircraft, often prior to it even being built. The parts that make up an aircraft all reference the individual MSN.
Multilateration is the process of using the time difference of arrival of radio signals from an aircraft to ascertain the aircraft's position and heading. MLAT requires four or more Flightradar24 receivers in a region to receive a signal from the same aircraft. From this we can then measure the Time Difference of Arrival (TDOA).
You can read more about MLAT here.
Mode S is a communication protocol that allows an aircraft to communicate with secondary surveillance radar (SSR) and other systems through its on-board transponder. Aircraft with a Mode S transponder are capable of utilizing TCAS and ACAS II functions.
A METAR is a specialized form of weather reporting used mainly in aviation. METARs are standardized by ICAO and follow a specified format so that they may be understood easily by pilots around the world. METARs differ from a Terminal Aerodrome Forecast (TAF) in that they provide actual weather at that time, rather than a forecast which a TAF provides. View a live METAR report here.
Mountainous Terrain Escape Routes
When a flight occurs over an area of high, mountainous terrain, it’s vital that escape routes are planned so that in an emergency situation an aircraft is able to descend to an altitude below the Minimum Obstacle Clearance Altitude (MOCA). Central Asia is a region where planned escape routes are regularly required due to the large areas of high terrain there.
Multifunction Control Display Unit (MCDU)
Multifunction Control Display Unit’s are typically found in Airbus aircraft and consist of a screen and keypad which the crew uses as an interface with the aircraft FMS (Flight Management System).
North Atlantic Tracks
North Atlantic Tracks, officially known as North Atlantic Organized Track System (NAT-OTS) are a specified set of routes that stretch Eastbound and Westbound across the North Atlantic. They provide separation for aircraft, as well as taking into account optimum weather conditions. In order to utilise these tracks aircraft require Oceanic clearance. Find out more about North Atlantic Tracks here.
Notice to Airmen (NOTAM)
A Notice to Airmen NOTAMs are issued by aviation authorities to alert pilots to hazards or other important information they need to navigate the area safely. NOTAMs are filed with a country's aviation authority and then disseminated through a range of channels to provide up to date information to pilots and operators. Take a look at some example NOTAMs here.
National Transportation Safety Board (NTSB)
The NTSB is a US government agency tasked with investigating civilian transport accidents. They predominantly investigate aviation incidents and accidents, but also marine, highway, rail, and pipeline investigations.
Non-directional beacon (NDB)
A Non-directional beacon (NDB) is a radio beacon which transmits morse code identification signal. Aircraft can use Automatic Direction Finding (ADF) equipment to then navigate between NDB's.
Primary Flight Display (PFD)
A primary flight display typically provides flight crew with data relating to airspeed, altitude, heading and vertical speed.
When discussing "radar", primary radar is generally what is being referred to. Primary radar outputs a radio signal and attempts to detect any reflection of that signal from an object, such as an airplane.
QNH is an aeronautical 'Q code' which provides a barometric altimeter setting relating to airfield elevation above mean sea level. Standard QNH which is used when flying at Flight Levels is set to 1013.25hPa / 29.92inHg.
QFE is an aeronautical 'Q code' which provides a barometric altimeter setting which causes an altimeter to read zero when at the reference datum point of an airfield.
An airport apron, known as a “ramp” in the US, is an area used for aircraft parking.
Registration / Tail Number
Each aircraft is assigned a registration number—often called a tail number—that is unique to the aircraft. Registration numbers are based on the country of registration, with the United Kingdom employing 'G' as their first letter identifier, followed by a hyphen and four further letters e.g. G-STBA. In the United States 'N' is used as the first letter followed by either letters or numbers e.g. N463UA.
Repositioning flights usually occur when an aircraft is out of place, either due to previous diversion or operational requirements.
Runway Visual Range (RVR)
Runway Visual Range is usually stated in feet (ft) or meters (m) and is the horizontal distance that pilots when positioned on the center line of a runway can see its surface markings or runway lights.
Secondary radar, or secondary surveillance radar, sends out a signal to compatible aircraft, which then return a signal of their own with information about a flight, such as speed, altitude, heading, and registration.
Speed, as it relates to aircraft, is more complicated than speed on the ground, as there are different ways to measure speed in flight. The different ways to measure speed can result in differences between the types, whereby the ground speed of an aircraft can vary significantly from its airspeed. The speed shown in the "speed" box on Flightradar24 for all aircraft is ground speed.
Standard instrument departure route (SID)
An SID is a published instrument flight rules (IFR) routing that pilots use directly after takeoff from an airport.
Standard arrival route (STAR)
A STAR is a published instrument flight rules (IFR) routing that pilots use prior to transitioning to their chosen approach and landing profile.
Each flight is assigned a four digit code, known as a squawk, by air traffic control. This code is unique to the flight and helps ATC identify each flight. There are a few significant squawk codes, which immediately get the attention of air traffic control. For a longer discussion of squawk codes and emergencies, please see our discussion with a pilot and an air traffic controller.
7600: Radio Failure
7700: General Emergency
A slot is a period of time lasting 15 minutes which is issued by Air Traffic Control in order to limit the amount of aircraft using certain airspace. The 15 minute period lasts from 5 minutes before to 10 minutes after the specific slot time.
Tactical Air Navigation System (TACAN)
A TACAN is an UHF navigation system which provides aircraft with a distance and bearing.
Terminal Area Forecasts are similar in format to METARs, but are issued for future periods. For major civil airports TAFs are issued every six hours, usually at 0000, 0600, 1200, 1800 UTC. Military TAFs are normally issued every three hours.
True Airspeed is the airspeed of an aircraft corrected for position and instrument error and taking pressure and temperature into account.
A Traffic Collision Avoidance System allows aircraft to communicate if equipped with a compatible transponder in order to prevent a mid-air collision. The TCAS warns pilots of traffic in the vicinity and can issue directives to help pilots maintain separation if flights come too close to one another.
Track is the aircraft's compass heading, denoted as 1-360. It's the real path, or vector, that the aircraft is flying. In order to work out an aircraft's track, heading +/- WCA (wind correction angle) gives the track.
A portmanteau of transmitter-responder, the transponder emits a radio signal based on an interrogation from an outside source, either air traffic control or another aircraft. In normal operation a pilot will be instructed by an air traffic controller to set a specific code on their transponder and when this happens the terminology used will be to 'squawk' a code e.g. "Speedbird 115 squawk 4552".
Vertical speed is the rate at which a plane is ascending or descending, often shown in feet/meters per minute. Generally, vertical speed during departure will range from 1000-3000 feet per minute, while during descent, speeds can be between 600-800 feet per minute.
Very High Frequency Omni-Directional Range (VOR)
A VOR, or Very High Frequency Omni-Directional Range is a short range radio navigation beacon. By using a network of VORs pilots can determine their position and course.
Visual Flight Rules (VFR)
Visual Flight Rules are a set of regulations whereby a pilot can operate an aircraft in weather which is suitable for visual reference only. The weather requirement for VFR flight is known as visual meteorological conditions (VMC). If the weather is below VMC minima a pilot can only proceed with flight using Instrument Flight Rules (IFR).
A yoke is the input device a pilot uses to control pitch and roll of an aircraft.