Every abbreviation, decoded

Above Aerodrome Level — height referenced to the airport elevation, not a specific runway threshold. Used for circling minima on ICAO plates.

Aircraft Communications Addressing and Reporting System — the VHF/satellite datalink network airliners use for company ops and ATC messages.

The transport layer: D-ATIS, PDC and CPDLC all travel over ACARS (or its modern successors). In MSFS, most study-level airliners simulate a Hoppie-based ACARS in the EFB or CDU.

Automatic Dependent Surveillance–Broadcast — the aircraft continuously broadcasts its position for ATC and other traffic.

Unlike ADS-C it needs no contract — it just broadcasts. Mandated in most controlled airspace; in the sim, online networks replicate it.

Automatic Dependent Surveillance–Contract — the aircraft automatically downlinks position reports to ATC where radar coverage ends.

Used over oceans and remote areas: ATC sets a "contract", the aircraft reports position, altitude and meteorological data on schedule or on demand. Runs alongside CPDLC over satellite.

Above Ground Level — height above the terrain directly below you.

On charts, AGL heights appear in parentheses: "564 (200)" means 564 ft MSL, which is 200 ft above the airport.

Aeronautical Information Publication — the official chart and procedure source of a country.

Every ICAO member state publishes an AIP containing all instrument procedures and airport charts. It is the authoritative source — commercial charts are re-renderings of this data.

The 28-day cycle on which all aviation navdata and charts are updated.

Approach category A–E based on Vat (1.3× stall speed at max landing weight) — decides which minima column applies.

A: <91 kt · B: 91–120 · C: 121–140 · D: 141–165 · E: 166–210 kt. In the sim, pick the column for your actual approach speed: a 737/A320 is CAT C, a 747/787 is D, a C172 is A.

Weather warning for lighter hazards — moderate icing, turbulence, mountain obscuration.

Top-down chart of an airport: runways, taxiways, aprons, hot spots — used for taxi.

The diversion airport in your back pocket — the OFP carries its own route, fuel and weather.

Actual Navigation Performance — the accuracy your aircraft computes it is achieving right now.

The FMS estimates its own position accuracy and shows it as ANP. Rule: ANP must stay at or below the RNP of the leg — if ANP exceeds it, you are outside the protected corridor and should go around.

Auxiliary Power Unit — the small turbine in the tail providing electrics and bleed air on the ground.

Approach procedure with Vertical guidance — the ICAO approach class between precision and non-precision: it has vertical guidance but does not meet the accuracy requirements of a precision system.

Typical APV minima types are LPV (SBAS) and LNAV/VNAV (barometric VNAV). APV approaches are flown to a DA like precision approaches — the difference is that the vertical path does not meet the accuracy and integrity requirements of a precision approach.

Air Route Traffic Control Center — the US enroute facility, always called "Center" on the radio.

Air Traffic Control — the service that separates and sequences aircraft.

Automatic Terminal Information Service — a recorded broadcast of weather and active runways.

Airway — a published route corridor between navaids or fixes, e.g. UL613.

AI air-traffic control for MSFS — voice-driven, with datalink clearances in supported setups.

The top band of a Jeppesen approach plate: frequencies, navaid, course and minimums in one strip.

Calibrated Airspeed — indicated speed corrected for instrument and position error.

ILS approach categories — how low the weather may be: CAT I (200 ft DA, 550 m RVR) down to CAT IIIC (no DH, no RVR).

CAT II: DH 100–200 ft, RVR ≥300 m · CAT IIIA: DH <100 ft, RVR ≥175 m · CAT IIIB: DH <50 ft or none, RVR below 175 m but at least 50 m · CAT IIIC: zero-zero, full autoland. Requires certified aircraft, crew and ground equipment.

Ceiling And Visibility OK — METAR shorthand: 10 km+ visibility, no significant weather, no cloud below 5,000 ft, and no CB/TCU at any height.

Cumulonimbus — the thunderstorm cloud. The only cloud that is an emergency by itself: hail, severe icing, extreme turbulence, windshear. Never penetrate one.

The only cloud type (besides TCU) named in a METAR: SCT020CB = scattered cumulonimbus at 2,000 ft. Tops can reach the tropopause — you fly around, never over or through.

Course Deviation Indicator — the needle showing how far you are off the selected course or radial.

The height of the lowest broken (BKN) or overcast (OVC) cloud layer above the airport — or vertical visibility (VV) into an obscuration. The number that decides VFR vs IFR.

Controlled Flight Into Terrain — a working aircraft flown into the ground; the accident MSA, MVA and approach minima exist to prevent.

Cost Index — how the FMS trades fuel against time: low = cheap/slow, high = fast/thirsty.

Visual maneuver to land on a different runway than the one the instrument approach serves.

Height gained per horizontal distance. The missed approach assumes a nominal 2.5% — some published minima are only valid if you can outclimb it.

Expressed as a percentage (ICAO) or ft per NM (FAA assumption: 200 ft/NM ≈ 3.3%). PANS-OPS designs the missed-approach obstacle surface at 2.5%; where terrain requires more, plates publish alternative OCA rows for steeper gradients (Innsbruck: 2.5/4.0/5.0%). On Lido minima tables, a "GA x.x%" column header means the same thing — go-around gradient. Mental math: % × 61 ≈ ft/NM; ft/min ≈ ground speed (kt) × % — 2.5% at 140 kt is about 350 ft/min. Above 2.5% it becomes an operator verification item: the aircraft must deliver it engine-out at the expected landing weight.

Controller–Pilot Data Link Communications — ATC clearances sent as text messages instead of voice.

Used for oceanic airspace and increasingly enroute (e.g. Maastricht). In MSFS: VATSIM controllers uplink through the Hoppie relay; AI services like SayIntentions and BeyondATC integrate natively in supported aircraft (Fenix, iniBuilds, PMDG).

Control Area — controlled airspace around or above an airport zone.

Common Traffic Advisory Frequency — the real-world self-announce frequency at uncontrolled airports; UNICOM is its VATSIM equivalent.

Control Zone — controlled airspace around an airport, from the surface up.

Decision Altitude / Height — the point on a precision approach where you decide: land or go around.

DA is referenced to MSL, DH to the runway threshold. Reaching DA without the runway environment in sight means an immediate missed approach.

Distance Measuring Equipment — shows slant distance in NM to a paired station.

Electronic Flight Bag — the cockpit tablet holding charts, performance tools and datalink settings.

In MSFS add-ons the EFB is where you import SimBrief, view charts and pick the CPDLC provider.

Estimated Fuel On Board — per-fix fuel prediction in the OFP flight log; your in-flight sanity check.

Estimated Time of Arrival.

Final Approach Fix — the last fix before the runway; the final segment starts here.

Final Approach Point — where the glide path is captured on an ILS; the precision counterpart of the FAF.

Cloud coverage in eighths of sky (oktas): FEW 1–2, SCT 3–4, BKN 5–7, OVC 8. Followed by the base height in hundreds of feet AGL — BKN016 = broken at 1,600 ft.

Final Reserve fuel — typically 30 min holding over the alternate; the untouchable minimum.

Flight Information Region — the airspace block an ATC center controls; also the CPDLC logon code.

A defined point in space, shown as a triangle/cross on charts; named with a five-letter code.

Flight Level — altitude on standard pressure in hundreds of feet: FL 350 is 35,000 ft.

Assumed temperature for reduced-thrust takeoff — saves engine wear while meeting all limits.

Flight Management System/Computer — holds route and performance data and flies the aircraft via the autopilot.

ICAO Flight Plan — the compact filed message encoding rules, aircraft, route and equipment.

General Aviation — everything that is not airline or military: private, training and business flying.

The vertical guidance beam of an ILS — typically a 3° path to the touchdown zone.

GBAS Landing System — a satellite-based precision approach; a ground station uplinks GPS corrections instead of beams at the runway.

You tune a five-digit GBAS channel, not a frequency. Flown like an ILS to a DA; operational GBAS is certified for CAT I — CAT II-capable GAST-D systems are standardized and entering service, CAT III is not yet certified. In MSFS mostly on study-level airliners.

Global Navigation Satellite System — GPS and friends; the sensor behind RNAV and RNP procedures.

Ground Proximity Warning System — the "TERRAIN, PULL UP" box; the enhanced version is EGPWS/TAWS.

Free community ACARS relay — the transport layer most sim datalink rides on, including VATSIM CPDLC.

Hoppie only moves messages; it provides no controllers itself. D-ATIS, PDC and CPDLC appear when a ground station (VATSIM/IVAO controller, AI service) is online at the other end.

Horizontal Situation Indicator — the compass-rose display showing course, heading and deviation.

Initial Approach Fix — where the instrument approach procedure officially begins.

Instrument Approach Procedure — the formal name for an approach plate.

Indicated Airspeed — what the instrument shows, before corrections.

International Civil Aviation Organization — sets worldwide standards (and the 4-letter airport codes).

The morse-code identifier of a navaid, used to verify you tuned the right station.

Intermediate Fix — the fix between IAF and FAF where you get established on final.

Instrument Flight Rules — flying by instruments and clearances, in any weather.

Instrument Landing System — localizer + glideslope, the most common precision approach.

Letter suffixes when several ILS procedures serve the same runway — they differ in transitions or missed approaches.

ICAO plates suffix variants: "ILS X", "ILS Y", "ILS Z" (then W, V…). The letter is just a label — the differences are in the missed approach, feeder routes or notes. Always brief the specific lettered chart you are flying.

Instrument Meteorological Conditions — weather requiring IFR flight.

International Standard Atmosphere — 15 °C, 1013 hPa, −2 °C per 1,000 ft; the reference behind performance numbers.

Commercial chart provider (a Boeing company) whose plate layout Navigraph uses in MSFS.

Free open-source moving map that reads the MSFS navdatabase — procedures, navaids, live position.

Lateral / Vertical Navigation — RNAV approach guidance levels; LNAV-only means an MDA.

The lateral guidance beam of an ILS — keeps you on the extended runway centerline.

Localizer Performance with Vertical guidance — a GPS/SBAS approach with near-ILS precision.

Missed Approach Point — the latest point to start a go-around on a non-precision approach.

Minimum Descent Altitude — the lowest altitude on a non-precision approach; level off until you see the runway.

Referenced to mean sea level. Expressed as a height above the aerodrome or threshold it is called MDH (Minimum Descent Height).

Minimum Enroute Altitude — lowest published airway altitude with nav-signal coverage and obstacle clearance.

The routine airport weather report — wind, visibility, clouds, QNH, temperature.

The published go-around procedure — a fully charted route to a safe altitude and holding fix.

Minimum Obstruction Clearance Altitude — clears obstacles, but only guarantees nav coverage near the station.

Minimum Off-Route Altitude — grid-box terrain clearance figure on enroute charts.

Minimum Sector Altitude — safe altitude within 25 NM of a navaid, shown as a dashed circle.

The MSA guarantees 1000 ft obstacle clearance within its sector. It is for orientation and emergencies — it is not part of the procedure path.

Mean Sea Level — the reference for altitudes on charts; what the altimeter reads on QNH.

Minimum Vectoring Altitude — the lowest altitude a radar controller may vector you at.

Any navigation aid — VOR, NDB, DME, localizer; the stations courses and fixes hang on.

Subscription service providing Jeppesen charts and navdata for MSFS.

Non-Directional Beacon — a simple radio beacon; the ADF needle always points at it.

Notice to Airmen (FAA: Notice to Air Missions since 2021) — time-critical changes: closed runways, inop navaids, hazards.

No Significant Cloud — METAR code: nothing below 5,000 ft and no CB/TCU. US equivalents: SKC (manual station), CLR (automated).

Obstacle Clearance Altitude / Height — the lowest altitude/height at which an approach still guarantees obstacle clearance. What ICAO AIP plates print instead of a DA.

Published by the state; the operator derives DA/MDA by adding regulatory and aircraft margins on top. Your minimum can never be lower than the OCA. OCA is referenced to MSL, OCH to the threshold or aerodrome elevation.

Operational Flight Plan — the dispatch release: route, fuel, weather, NOTAMs for one specific flight.

Precision Approach Path Indicator — four lights beside the runway; two red, two white means on path.

Pre-Departure Clearance — your IFR clearance delivered as a datalink message instead of a voice readback.

Also called DCL (Datalink Departure Clearance). Request it via the aircraft ACARS/EFB; the clearance arrives as text — route, squawk, departure runway — that you load into the FMS. In the sim: Hoppie, VATSIM or BeyondATC provide it at equipped airports.

The top-down map section of an approach plate — fixes, courses, terrain, MSA.

The side-view section of an approach plate — altitudes and the descent path.

Altimeter setting that reads zero on the runway — height above the field. Rare outside older/Russian ops.

The altimeter reading with standard 1013 hPa set — above the transition altitude that reading is a flight level.

Local altimeter setting (sea-level pressure); set it and the altimeter reads MSL altitude.

Above the transition altitude you switch to standard 1013 hPa / 29.92 inHg and fly flight levels.

Radio Altitude — height above terrain from the radio altimeter; the reference for CAT II/III callouts. (In a METAR, RA means rain; in a TCAS context, resolution advisory.)

Receiver Autonomous Integrity Monitoring — the GPS checking its own accuracy; required for RNAV approaches.

Repeating a clearance or instruction back to ATC — mandatory for runways, levels, headings, speeds, squawks and altimeter settings.

Area Navigation — flying between GPS-defined waypoints instead of station-to-station.

Required Navigation Performance — the accuracy a procedure demands, e.g. RNP 0.3 = stay within 0.3 NM.

RNP is the requirement printed on the chart; ANP is what your aircraft actually achieves. The aircraft must monitor and alert when ANP > RNP — that alerting is what separates RNP from plain RNAV.

RNP with Authorization Required — curved RF legs and tight containment for crews and aircraft with special approval.

Allows curved approaches through terrain (e.g. Queenstown). The plate shows RNP values per segment; both aircraft certification and crew training are mandatory.

Runway Visual Range — visibility measured along the runway, in metres (FAA reports it in feet).

Runway.

Subscription AI-ATC service with CPDLC/datalink support in supported aircraft.

Standard Instrument Departure — a published route from the runway to the enroute structure.

Significant weather warning — thunderstorms, severe icing, turbulence, volcanic ash.

Free flight-planning tool widely used with MSFS; generates dispatch briefings and routes.

Special METAR issued between routine reports when weather changes significantly.

Four-digit transponder code assigned by ATC — read it back digit by digit and set it in the transponder.

Unlawful interference (hijack) transponder code — never set it, even for fun. On VATSIM it can get you a call from a supervisor.

Radio-failure transponder code — ATC sees you cannot hear them and works you in via light signals and separation from others.

Emergency transponder code — tells every radar screen you have a general emergency. Usually paired with a MAYDAY call.

Standard Instrument Arrival (FAA: Standard Terminal Arrival Route) — a published route from the enroute structure to the approach area.

Tactical Air Navigation — the military counterpart to VOR, providing bearing and distance; at shared stations (VORTAC) civil aircraft use its paired DME.

Terminal Aerodrome Forecast — the airport weather forecast, 24–30 hours ahead.

True Airspeed — your real speed through the air after altitude/temperature correction.

Traffic Alert and Collision Avoidance System — interrogates other transponders and issues climb/descent advisories.

Threshold Crossing Height — the glide path height over the runway threshold, e.g. 55 ft.

Towering Cumulus — cumulus congestus, a cumulus growing taller than it is wide. The stage right before a thunderstorm.

The second cloud type named in METARs (FEW040TCU). ICAO-specific abbreviation for cumulus congestus of great vertical extent.

Touchdown Zone — the first 3,000 ft of runway; also an elevation reference on plates.

Terminal Control Area — the controlled-airspace funnel around a busy airport.

Top of Descent — where cruise ends and the descent begins; the FMS computes it.

The altitude where you switch from QNH to standard pressure (1013 hPa). Varies by country.

Self-announce frequency (122.800 on VATSIM) used when no controller is online — state position and intentions for other traffic.

Coordinated Universal Time — "Zulu"; flight plans, NOTAMs and clearances all run on it.

V1 (decision), VR (rotate), V2 (takeoff safety) — the takeoff speeds from the runway analysis.

Visual Approach Slope Indicator — the older light system like PAPI: "red over white, you're all right".

The largest online flight-sim network — real people controlling real airspace around you.

Controllers on VATSIM can send CPDLC uplinks to equipped aircraft. Voice is the baseline, datalink is the upgrade.

Visual Descent Point — on FAA plates, where you may leave MDA for a normal descent to the runway.

Visual Flight Rules — flying by looking outside, with prescribed visibility and cloud clearance.

Very High Frequency — the 118–137 MHz band carries voice comms; VOR and ILS localizers sit just below it at 108–117.95 MHz (ILS glideslopes are UHF).

Visual Manoeuvring (Circling) — the minima row on ICAO plates for circling to land on another runway after the instrument approach. Printed as "VM(C) OCA (OCH AAL)".

Not to be confused with VMC (Visual Meteorological Conditions) — the unfortunate ICAO abbreviation means circling.

Visual Meteorological Conditions — weather good enough to fly VFR.

VHF Omnidirectional Range — a station radiating 360 radials you can navigate along.

Vertical Visibility — reported in a METAR (e.g. VV002 = 200 ft) when the sky is totally obscured and no cloud layers can be observed; it acts as the ceiling.

Will comply — the standard CPDLC reply that accepts a clearance. Its counterpart is UNABLE.

When a CPDLC uplink requires a response you typically get WILCO, UNABLE or STANDBY. Only answer STANDBY if you genuinely need time — the clearance is not in force until you WILCO.

Zero-fuel, takeoff and landing weight — the three masses every OFP lists against their limits.