Aviation terms explained

Plain-English definitions of the technical terms you'll see in Flight Mapper and elsewhere in flight planning. Sorted alphabetically.

A

AGL — Above Ground Level

An altitude measured from the local ground surface, not from sea level. A pattern altitude of 1,000 ft AGL means 1,000 feet above the airport, not above the ocean.

AIRAC — Aeronautical Information Regulation And Control

The 28-day publication cycle used worldwide for aeronautical data updates (charts, navigation databases, procedures). Every 28 days a new AIRAC cycle becomes effective on the same Thursday globally.

ATC — Air Traffic Control

The service that separates and sequences aircraft, both en route and around airports. Issues clearances, vectors, altitude assignments, and approach instructions.

B

Bearing

The horizontal direction from one point to another, measured in degrees clockwise from north. True bearing uses true north; magnetic bearing uses magnetic north (compensating for magnetic variation).

Block Time

Total time from when the aircraft first moves under its own power (off-blocks) until it stops at the destination gate (on-blocks). Includes taxi time, not just airborne time. Always longer than flight time.

C

Cruise Speed

The aircraft's typical speed in level flight at cruise altitude. Often expressed in knots or as a Mach number. Mid-size jets typically cruise at 430-470 knots (Mach 0.78-0.82).

D

Diversion Airport

An alternate airport selected during planning in case the destination becomes unavailable (weather, runway closure, emergency). Must meet specific fuel and weather minimums.

E

EFB — Electronic Flight Bag

An electronic device (typically an iPad) carrying charts, manuals, and flight planning tools — replacing the paper kit pilots used to carry. ForeFlight and Jeppesen FliteDeck are common EFB apps.

ETOPS — Extended-range Twin-engine Operational Performance Standards

Regulations governing how far a twin-engine aircraft may fly from a suitable diversion airport. ETOPS-180 means the aircraft is approved to fly up to 180 minutes from the nearest divert. Enables transoceanic operations with two engines instead of three or four. In Flight Mapper, range rings can visualize ETOPS coverage.

F

FBO — Fixed Base Operator

A commercial business at an airport providing services to general and business aviation: fueling, hangaring, ground handling, passenger lounges, crew facilities. Major brands include Signature, Atlantic, and Jet Aviation.

FIR — Flight Information Region

A defined volume of airspace within which a specific country provides flight information and alerting services. Crossing FIR boundaries usually requires permits and ATC handoffs.

Flight Level — FL

An altitude based on a standard pressure setting (29.92 inHg / 1013.25 hPa), used at high altitudes worldwide. FL350 means 35,000 feet. Pilots transition from local altimeter setting to FL above the transition altitude (typically 18,000 ft in the US, 5,000 ft in Europe).

G

Great Circle

The shortest path between two points on a sphere, lying along a circle whose center is the center of the sphere. On Earth, this is the actual shortest distance — and what Flight Mapper draws between every pair of airports. Looks curved on a flat (Mercator) map but is a straight line in 3D space.

Great Circle Distance

The length of the great circle path between two points, measured along Earth's surface. Almost always shorter than a "rhumb line" (constant-heading) route, especially for long east-west flights at high latitudes. Flight Mapper computes this using the haversine formula.

Ground Speed — GS

The aircraft's actual speed over the ground, equal to true airspeed adjusted for wind. A 450 KT cruise with a 50 KT tailwind = 500 KT ground speed.

H

Heading

The direction the aircraft's nose is pointing, in degrees. Different from track (the direction it's actually moving over the ground) when there's a crosswind.

I

IATA — International Air Transport Association

An airline trade organization, but in flight planning the term usually refers to IATA codes — three-letter airport codes used by airlines and passengers (LAX, JFK, GRU, LHR). Easier to remember than ICAO codes but only cover commercial airports.

ICAO — International Civil Aviation Organization

A UN agency setting standards for international civil aviation. ICAO codes are four-letter airport identifiers (KLAX, KJFK, SBGR, EGLL) used in flight plans, ATC, and operational documents. The first letter or two indicate region: K = mainland US, EG = UK, SB = Brazil, etc. Cover virtually every airport in the world.

K

Knot — KT or KTS

One nautical mile per hour. The standard speed unit in aviation worldwide. 100 knots ≈ 115 mph ≈ 185 km/h.

M

Mach Number

Aircraft speed expressed as a fraction of the speed of sound. Mach 1.0 at sea level ≈ 661 KT, but decreases with altitude. At cruise altitude (FL350+), Mach 1.0 ≈ 574 KT. Business jets cruise at Mach 0.74-0.85.

METAR — Meteorological Aerodrome Report

A standardized weather report issued each hour (or more often) for an airport. Includes wind, visibility, ceiling, temperature, dewpoint, altimeter, and remarks. Pilots check the METAR before every flight.

N

NM — Nautical Mile

A unit of distance equal to one minute of latitude (1/60 of a degree) along any meridian. Equals 1.852 km or 1.151 statute miles. The standard unit for distance in aviation and maritime navigation.

NOTAM — Notice to Air Missions

Time-critical aeronautical information that wouldn't fit a chart update cycle: runway closures, VIP movements, navaid outages, GPS interference. Pilots must check NOTAMs for every airport on their route.

O

Overflight Permit

Permission from a country to fly through its airspace without landing. Required for most international flights crossing third countries. Some countries (USA, EU members, Canada) generally don't require permits; others (China, Russia, many in Africa and Middle East) always do.

P

PWA — Progressive Web App

A web app that can be installed on a phone or tablet and behave like a native app — home screen icon, standalone window, offline support. Flight Mapper is a PWA.

R

Range Ring

A circle drawn on a map at a constant distance (or flight time) from a chosen center, used to visualize an aircraft's reachable area. Useful for fuel reserve planning, ETOPS coverage, ferry analysis, or "where can I divert from here?"

Reserve Fuel

Fuel beyond what's needed to fly the planned route, required by regulation. Includes contingency (typically 5%), alternate fuel, holding fuel (often 30-45 minutes), and final reserve (30 minutes for IFR domestic, 45 for international).

S

SID — Standard Instrument Departure

A pre-published departure procedure from an airport, designed to safely route aircraft from runway to en-route airspace. Identified by name and revision letter (e.g., GRU 9R BANBA1A).

T

TAS — True Airspeed

The aircraft's actual speed through the air mass, accounting for altitude and temperature. A jet showing 300 KT indicated airspeed at FL400 has a true airspeed of about 470 KT due to thinner air.

Trip Sheet

A summary document used for charter or business jet flights, listing route, times, passengers, crew, fuel load, alternates, and other essentials. Often distributed to crew and operations 24 hours before departure.

V

VFR — Visual Flight Rules

A set of regulations under which a pilot operates by visual reference to the ground and other aircraft. Requires good weather (specific minimums for visibility and cloud distance).

W

Waypoint

A specific geographical point used for navigation, defined by latitude/longitude or a named identifier. Routes are usually defined as a sequence of waypoints, not just origin and destination.

Z

Zulu Time — UTC

Coordinated Universal Time, the time standard used worldwide in aviation. Avoids confusion across time zones. A flight departing "0830Z" departs at 08:30 UTC regardless of local time.

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