Aviation glossary

Plain-English definitions of the terms, abbreviations and codes you'll meet across weather reports, navigation, performance and air law. 8 terms and counting.

B

BECMG

Weather

BecomingBECMG indicates a steady, self-contained shift. The weather will start changing at the beginning of the period and officially "become" the new conditions by the end of the period. BECMG is always followed by a 4-digit start and end time (in UTC/Zulu time) indicating when the gradual change is in progress.

F

FM

Weather

FromFM signals a rapid, complete change of conditions at a specific time. Everything stated after FM replaces the previous forecast from that time onward.

M

METAR

Weather

Meteorological Aerodrome ReportA METAR is a coded observation of current weather conditions at an aerodrome, issued routinely (usually every 30 or 60 minutes) and covering wind, visibility, weather, cloud, temperature, dew point and pressure.

P

PROB

Weather

ProbabilityPROB gives the percentage probability of an alternative set of conditions occurring, usually PROB30 or PROB40. It is often combined with TEMPO to show the chance of temporary conditions.

Q

QFE

Weather

The altimeter pressure setting that causes the altimeter to read zero when the aircraft is on the aerodrome reference point. With QFE set, the altimeter reads height above that datum.

QNH

Weather

The altimeter pressure setting that causes the altimeter to read aerodrome elevation above mean sea level when the aircraft is on the ground. With QNH set, the altimeter reads altitude.

T

TAF

Weather

Terminal Aerodrome ForecastA TAF is a concise, coded forecast of expected weather at an aerodrome over a defined validity period (typically 9, 24 or 30 hours), describing wind, visibility, weather and cloud along with any expected changes.

TEMPO

Weather

TemporaryTEMPO marks temporary fluctuations expected to last less than an hour each and, in total, less than half of the indicated period. Conditions are expected to return to the prevailing forecast in between.