Glossary

A descent-planning rule of thumb that allows about 3 nautical miles of track distance for every 1000 feet to lose, giving a path of roughly 3 degrees.

A system in which an aircraft automatically broadcasts its own position, derived from on-board navigation such as GPS, without being interrogated; ADS-B Out transmits and ADS-B In receives.

The official manual of lasting aeronautical information for a State, organised into the GEN, ENR and AD parts under the ICAO framework.

A system of common worldwide effective dates, spaced 28 days apart, on which planned changes to aeronautical data take effect together.

A warning of less severe en-route weather that mainly affects lighter aircraft and visual flight, such as moderate turbulence, moderate icing or widespread reduced visibility.

The ICAO classes of airspace, A to G, that set which flights are allowed, whether they are separated, whether a clearance is needed and what service is provided.

An aerodrome you plan to divert to if you cannot land at the destination; whether one is required, and the weather it must have, differ by authority and operation.

The distance available to accelerate for take-off and then stop, for a runway direction: the take-off run plus any stopway beyond it.

A broadcast that bundles the current weather with operational information you cannot get from a METAR, such as the runway and approach in use.

A METAR or TAF term that replaces the visibility, weather and cloud groups when visibility, cloud and present weather all meet its defined good-weather conditions.

A technique for flying the final segment of a non-precision approach as a single continuous descent with no level-off, from the final approach fix down to near the threshold.

The point at which an aircraft's mass effectively balances; it has to stay within the forward and aft limits the manufacturer publishes.

The period of partial light after sunset and before sunrise that the rules use to define when night begins and ends for logging flight time.

The tendency of a pressure altimeter to over-read in colder-than-standard air, so that true altitude is lower than indicated; corrections are added to minimum altitudes on instrument procedures in cold conditions.

The part of the reported wind acting across the runway, worked out from the wind speed and its angle to the runway heading.

Pressure altitude corrected for non-standard temperature: the altitude in the standard atmosphere at which the air density equals the density you actually have.

The air temperature minus the dewpoint, a measure of how close the air is to saturation; a small spread means fog or low cloud is more likely.

The period from reporting for a flight or series of flights until the aircraft comes to rest at the end of the last sector; it includes flight time plus the ground time between sectors.

An altitude read on the standard pressure setting, so all aircraft in the upper airspace share one common reference.

The rules that limit flight time, duty and the flight duty period and require minimum rest, to manage crew fatigue; the figures differ by authority.

Fuel carried beyond what the trip needs so a flight does not land with empty tanks; the required amount differs by authority and operation.

The worldwide method for assessing and reporting a runway surface condition, using a runway condition code and a matching braking-action description for each third of the runway.

A racetrack-shaped path that keeps an aircraft within a defined piece of airspace while it waits, defined by a fix, an inbound course and a turn direction.

A three-letter airport code (or two-letter airline code) used commercially, on tickets and baggage tags, such as LHR. Distinct from the four-letter ICAO location indicator used to operate the flight.

The international standard form for filing a flight, including Item 10 for equipment and capabilities and Item 18 for other information.

The four-letter operational code for an aerodrome, such as EGLL, used in flight plans, ATC, weather reports and charts. It is regionally structured, unlike the three-letter IATA code.

Flight conducted under instrument flight rules; also one of the colour-coded flight categories, with a low ceiling and/or reduced visibility.

Time spent controlling the aircraft solely by reference to the instruments, in actual or simulated conditions; being on an IFR flight plan in clear air does not count.

A defined reference atmosphere, 15 degrees Celsius and 1013.25 hectopascals at mean sea level with a standard lapse rate, used as the common yardstick for altimetry, performance and true airspeed.

A line on a surface analysis chart joining places of equal mean sea level pressure. The closer the isobars, the stronger the pressure gradient and the stronger the wind.

A unit of speed equal to one nautical mile per hour, used for wind and airspeed.

The landing distance available for a runway direction; it can be shorter than the runway if the threshold is displaced.

The most restrictive of the colour-coded flight categories, with a very low ceiling and/or very low visibility.

True airspeed expressed as a fraction of the local speed of sound, so it has no units. Because the speed of sound falls with temperature, the same true airspeed is a higher Mach number in the colder air aloft.

A routine observation of the weather actually measured at an aerodrome, issued in a standard coded form.

A transponder mode that adds a unique 24-bit aircraft address and a data link and lets a radar interrogate one aircraft selectively; it is the basis for ADS-B. Mode A sends the code, Mode C adds pressure altitude.

A flight category between VFR and IFR, with a ceiling and/or visibility lower than VFR but better than IFR.

The unit of distance used in aviation and at sea.

A notice about the establishment, condition or change of an aeronautical facility, service, procedure or hazard that is essential to flight operations.

The unit cloud cover is reported in, meaning eighths of the sky; the METAR amounts FEW, SCT, BKN and OVC each map to a range of oktas.

Markings in a NOTAM end-time field: PERM means the change is permanent and will later go into the AIP, while EST means the end time is only an estimate and can be outlasted.

Limits a pilot sets for themselves, deliberately more conservative than the legal or aircraft minimums, allowing for their experience, currency, the aircraft and the conditions on the day.

A packaged set of the NOTAM information relevant to a flight, prepared before departure; a snapshot that has to be refreshed close to departure.

The pilot legally responsible for the operation and safety of a flight; note that logging PIC time is a separate question from being the acting pilot in command.

A report from a pilot of the conditions actually met in flight, such as turbulence, icing, cloud tops, visibility, wind and temperature.

The five-letter code in a NOTAM Q-line: the second and third letters give the subject and the fourth and fifth the condition or status.

The pressure setting that makes the altimeter read height above a chosen datum, usually the aerodrome, so on the ground it reads about zero.

Flying on the standard pressure setting so the altimeter reads pressure altitude; it is the common reference for flight levels in the upper airspace.

The pressure setting that makes the altimeter read altitude above mean sea level, so on the ground it shows the elevation of the aerodrome.

The table that maps the type and depth of a runway contaminant to a runway condition code and the matching braking-action word.

The recent experience the rules require, such as recent take-offs and landings, before you carry passengers or fly at night or on instruments.

A continuous, uninterrupted period free of all duties and able to be used for sleep; a minimum rest is required before a duty, set by your authority.

A single digit from 6 down to 0 describing a runway third under the Global Reporting Format, where 6 is a dry runway and lower numbers mean less braking and directional control.

A warning of weather hazardous to all aircraft, such as severe turbulence, severe icing, thunderstorms, volcanic ash or a tropical cyclone.

A special weather observation issued between routine METARs when the weather changes significantly, using the same code form.

The four-digit transponder code (each digit 0 to 7) that identifies an aircraft to secondary surveillance radar. Three codes are reserved worldwide: 7700 emergency, 7600 radio failure, 7500 unlawful interference.

An approach flown on the correct path, speed and configuration by defined gate heights, with a go-around if the gate is not met.

Time you are required to be available for an assignment; airport standby counts as duty in full, while standby at home is treated more leniently.

Large supercooled droplets, the size of freezing drizzle or rain, that can run back behind protected surfaces and freeze there; many aircraft are not certified for them.

A forecast of the weather expected at an aerodrome over a stated validity period, using change groups to show how it is expected to change.

The take-off distance available for a runway direction: the take-off run plus any clearway beyond it.

The point at which an aircraft leaves the cruise to begin a planned descent, commonly estimated with the 3:1 rule of about 3 nautical miles per 1000 feet to lose.

The runway length available for the take-off ground run.

The altitude, on QNH, at which you change to the standard pressure setting while climbing.

The aircraft's actual speed through the air: calibrated airspeed corrected for air density. Because density falls with altitude, true airspeed is higher than the indicated speed up high.

Flight conducted with visual reference to the ground and horizon under the visual flight rules; also the most permissive of the colour-coded flight categories.

The minimum flight visibility and distance from cloud required to fly under visual flight rules; the figures depend on airspace and altitude and differ by authority.

The trailing wingtip vortices a wing sheds while making lift, strongest behind a heavy, slow, clean aircraft. ICAO groups aircraft into Light, Medium, Heavy and Super categories by take-off mass to set the separation behind them.

A change in wind speed or direction over a short distance, most dangerous close to the ground on take-off and approach where there is little height to recover.

The part of the night when the human body is least alert and most wants to sleep, so duty through it is more fatiguing and the rules allow less.