ATC glossary

Key air traffic control and approach-radar terms, in plain English.

These are the terms you'll meet as an approach controller — in the ATC Radar Simulator, on the radar, and in the guide.

Approach control (APP): The radar unit that sequences and separates arriving and departing aircraft within a terminal area, between the en-route centre and the aerodrome tower.
Area control centre (ACC): En-route radar control that works traffic at higher levels between terminal areas, across a flight information region (FIR).
Terminal area (TMA/CTA): The controlled airspace around one or more busy airports where approach control operates.
FIR: Flight Information Region — a large block of airspace within which flight information and alerting services are provided; worked by an ACC.
PPI: Plan-Position Indicator — the circular radar scope showing a top-down view with the radar site at the centre and a rotating sweep.
Data block: The label next to a radar target showing callsign, altitude, speed and other flight data.
Separation: The minimum spacing kept between aircraft — typically 3 NM horizontally (5 NM en-route) or 1,000 ft vertically.
STCA: Short-Term Conflict Alert — an automated warning when two aircraft are predicted to lose separation.
Vectoring: Assigning headings to steer an aircraft, e.g. onto final approach or clear of conflicting traffic.
Heading: The compass direction the aircraft nose points, in degrees; issued as "fly heading two seven zero".
Altitude: Vertical distance above mean sea level in feet, set on the local QNH; used below the transition level.
Flight level (FL): Altitude on the standard pressure setting (1013 hPa), flown at or above the transition level — e.g. FL100 = 10,000 ft.
Transition level / altitude: The boundary between flying altitudes (on QNH) and flying flight levels (on standard pressure).
QNH: The altimeter pressure setting that makes the altimeter read height above mean sea level.
ILS: Instrument Landing System — precision approach giving lateral (localizer) and vertical (glideslope) guidance to the runway.
Localizer: The ILS component giving left/right guidance along the extended runway centreline.
Glideslope: The ILS component giving the vertical descent path to the runway, usually 3°.
RNP / RNAV: Area-navigation approaches flown on GPS/onboard navigation rather than ground-based ILS.
SID: Standard Instrument Departure — a published route from the runway out to the en-route airways.
STAR: Standard Terminal Arrival Route — a published route from the airways in toward the approach.
IAF: Initial Approach Fix — where the instrument approach procedure begins.
Final approach: The last, straight-in segment aligned with the runway, usually on the ILS.
Downwind / base leg: Legs of the traffic pattern: downwind runs parallel to the runway, base turns from downwind onto final.
Holding pattern: A racetrack-shaped path flown over a fix to delay an aircraft until there is room in the sequence.
Waypoint / fix: A named position in the sky (five letters, e.g. LORNI) used to define routes and procedures.
Airway: A published "road in the sky" connecting navaids and fixes that aircraft follow en-route.
VOR: VHF Omnidirectional Range — a ground navaid giving aircraft a bearing to/from the station.
NDB: Non-Directional Beacon — an older ground navaid that aircraft can home toward.
DME: Distance Measuring Equipment — gives slant-range distance to a navaid, often paired with a VOR/ILS.
Radial: A magnetic bearing outbound from a VOR, used to define positions and routes.
Squawk / transponder: The 4-digit code an aircraft sets on its transponder so the radar can identify it.
Mode C / ADS-B: Surveillance sources: Mode C reports pressure altitude; ADS-B broadcasts precise GPS position.
Wake turbulence: The rotating air left behind an aircraft; heavier types need extra spacing behind them.
Go-around / missed approach: A discontinued landing where the aircraft climbs away to try again or hold.
Overflight: Traffic that crosses the sector without landing or departing there.
Handoff: Transferring control of a flight to the next unit — the tower, the next sector or an approach unit.
Radar contact: The controller's confirmation that an aircraft is identified on radar.
Ground speed: The aircraft's speed over the ground (airspeed adjusted for wind) — what you see on radar.
R/T: Radiotelephony — voice communication between controllers and pilots using standard phraseology.
7500 / 7600 / 7700: Emergency squawk codes: 7500 unlawful interference, 7600 radio failure, 7700 general emergency.
Callsign: The name a flight uses on the radio — an airline telephony word plus the flight number, e.g. "Speedbird 117" for BAW117.
Tower (TWR): The aerodrome control unit that owns the runway: it clears aircraft to take off and land. Approach hands arrivals to the tower on short final.
Ground control (GND): The unit that controls aircraft taxiing on the aprons and taxiways, before take-off and after landing.
Clearance: A formal authorisation from ATC — to fly a route, a level, a heading or an approach. Pilots may not deviate from it without asking.
Readback: The pilot repeating a clearance word-for-word so the controller can catch any misunderstanding — mandatory for safety-critical items.
ATIS: Automatic Terminal Information Service — a looped broadcast of the airport weather, runway in use and other essentials, updated regularly.
METAR: The standard coded weather report for an aerodrome: wind, visibility, cloud, temperature and pressure, issued every 30–60 minutes.
Runway designator: Runways are named by their magnetic heading rounded to tens: runway 31 points about 310°. Parallel runways add L, C or R — e.g. 31L and 31R.
Knot (kt): One nautical mile per hour — the standard unit of speed in aviation. 250 kt is about 460 km/h.
Nautical mile (NM): The standard aviation distance unit: 1.852 km, one minute of latitude. Radar separation is measured in NM.
IAS / TAS: Indicated airspeed is what the aircraft’s instruments read; true airspeed is its real speed through the air, higher at altitude where the air is thin.
Mach number: Speed as a fraction of the speed of sound, used at high altitude — e.g. Mach 0.82. Below roughly FL250 controllers assign knots instead.
Standard pressure (1013): The fixed altimeter setting (1013.25 hPa / 29.92 inHg) used at and above the transition altitude, so all aircraft fly comparable flight levels.
IFR: Instrument Flight Rules — flying by instruments and ATC clearances, in any weather. All airline traffic in the simulator is IFR.
VFR: Visual Flight Rules — navigating by looking outside, staying clear of cloud. Mostly light aircraft; kept apart from IFR flows.
Flight plan: The filed description of a flight: callsign, aircraft type, route, cruising level and destination. It is what shows up on the controller’s strip.
Control zone (CTR): The controlled airspace immediately around an airport, from the surface up — the tower’s domain.
Sector: A controller’s slice of airspace. Busy airspace is split into sectors, each with its own frequency, handed from one to the next.
Primary / secondary radar: Primary radar (PSR) paints raw echoes off the aircraft’s skin; secondary radar (SSR) interrogates the transponder and gets identity and altitude back.
Mode S: A modern transponder mode that gives each aircraft a unique address and richer data, reducing garbled replies on busy frequencies.
Squawk ident: An instruction to press the transponder IDENT button, which momentarily highlights the aircraft on radar to confirm which target it is.
MVA: Minimum Vectoring Altitude — the lowest altitude a controller may assign in each area, guaranteeing clearance from terrain and obstacles.
MSA: Minimum Sector Altitude — the published safe altitude within 25 NM of a navaid, used when arriving without radar guidance.
Intercept heading: A heading angled (usually ≤30°) toward the final approach course so the aircraft joins the localizer smoothly rather than crossing through it.
Established: Confirmed on the intended track — “established on the localizer” means the aircraft has captured final approach guidance.
Cleared for approach: The clearance that lets the pilot leave the last assigned level and follow the approach procedure down to the runway.
FAF: Final Approach Fix — the point where the final descent to the runway formally begins on an instrument approach.
Decision height (DH/DA): The altitude on final at which the crew must see the runway environment or go around — about 200 ft on a CAT I ILS.
Outer marker: A radio beacon (or equivalent fix) a few miles out on final, roughly where the glideslope is intercepted.
Stack: A holding pattern used by several aircraft at once, separated by 1,000 ft — arrivals descend through the stack as the lowest one leaves.
EAT: Expected Approach Time — the time an aircraft in a hold can expect to leave it and begin its approach; lets the crew plan fuel.
250 below 10,000: A near-universal speed limit: at most 250 kt IAS below 10,000 ft (FL100), keeping the busy lower airspace slower and safer.
Heavy / Super: Radio suffixes for wake category — “Speedbird 117 Heavy”. Heavies (like the 777) and Supers (A380) need extra spacing behind them.
Expedite: ATC word asking for the manoeuvre at best rate — “expedite descent” means come down quickly, without delay.
Direct to: A shortcut clearance: leave the published route and fly straight to a named waypoint — “proceed direct LOGAN”.
Level bust: Climbing or descending through the cleared level without clearance — a serious deviation that can erode separation.
Loss of separation: When two aircraft get closer than the required minima. The controller’s core job is to make sure this never happens.
TCAS / RA: The Traffic Collision Avoidance System on board each airliner; a Resolution Advisory commands an immediate climb or descent, and pilots follow it even against ATC.
Coordination: Controllers agreeing conditions between sectors — levels, routes and timing — before traffic crosses the boundary.
MAYDAY / PAN PAN: “MAYDAY” declares a life-threatening emergency; “PAN PAN” an urgent problem that is not (yet) life-threatening. Both get priority handling.
Altitude / height / elevation: Altitude is measured above mean sea level, height above the ground beneath, elevation is the ground’s own altitude — an airport at 656 ft elevation.
QFE: An altimeter setting that makes the altimeter read height above the airfield itself — zero on touchdown. Most airline flying uses QNH instead.

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