GEN 2.1  Measuring System, Aircraft Markings, Holidays


The table of units of measurement shown below are used by aeronautical stations within Brussels FIR/UIR for air and ground operations:

For measurement ofUnits used
Distance used in navigation, position reporting, etc
(generally in excess of 2 nautical miles)
Nautical miles (NM) and tenths
Relatively short distances such as those relating to aerodromes (e.g. runway lengths)Metres (M)
Altitudes, elevations and heightFeet (FT)
Horizontal speed, including wind speedKnots (KT)
Vertical speedFeet per minute (FPM)
Wind direction for landing and take-off Degrees magnetic (°)
Wind direction, except for landing and take-off Degrees true (°)
Visibility, including RVR Kilometres or metres (KM or M)
Visibility, including RVR (MIL)Kilometres or metres (KM or M) or nautical miles (NM) and tenths
Altimeter settingHectopascal (HPA)
TemperatureDegrees Celsius (°)
WeightMetric tonnes (T) or kilogrammes (KG)
Weight (MIL)Pounds or kilogrammes (KG)
TimeHours and minutes, beginning at midnight UTC


Co-ordinated Universal Time (UTC) and the Gregorian calendar are used by air navigation services and in publications issued by the AIS. Reporting of time is expressed to the nearest minute, e.g. 12:40:35 is reported as 1241.

Due to the application of daylight saving time, the relation between UTC and local time is different during summer and the winter period. The summer period starts every year on the last SUN of MAR at 0100 UTC and ends on the last SUN of OCT at 0100 UTC.

During the winter period, local time is UTC + 1 HR. During the summer period, local time is UTC + 2 HR.

In the AIP and in AIC, UTC times applicable during the summer period will be added between brackets when different from those applicable during the winter period.

SUP will mention UTC times as applicable during their period of validity. If the period of validity overlaps the transition from summer to winter period or vice versa, the system used in the AIP will be applied.

NOTAM will mention UTC times as applicable during their period of validity. If the period of validity overlaps the transition from summer to winter period or vice versa, a separate NOTAM will be published for each time period.


All published geographical co-ordinates indicating latitude and longitude are expressed in terms of the World Geodetic System of 1984 (WGS-84) geodetic reference datum.

An asterisk (*) will be used to identify those published geographical co-ordinates which have been transformed in to WGS-84 co-ordinates but whose accuracy of original field work does not meet the requirements in ICAO Annex 11, Chapter 2 and ICAO Annex 14, Volumes I and II, Chapter 2.


Mean sea level datum (MSL) is used as the vertical reference system. Values refer to the Earth Gravitational Model 2008 (EGM2008).

In addition to elevation values referenced to MSL, geoid undulation (referenced to the WGS-84 ellipsoid) is published for specific surveyed ground positions.


The nationality mark for civil aircraft registered in Belgium is the letter combination “OO” and for civil aircraft registered in Luxembourg, the letter combination “LX”. The nationality mark is followed by a hyphen and a registration mark consisting of:

  • three letters and/or numbers or a combination of those for Belgium (e.g. OO-SDN / OO-112 / OO-A02),
  • three letters for Luxembourg (e.g. LX-LAA).


New Year's Day01 JANBelgium and Luxembourg
Easter Monday-Belgium and Luxembourg
King's Birthday15 APRBelgian Defence
Labour Day01 MAYBelgium and Luxembourg
Europe Day09 MAYLuxembourg
Ascension Day-Belgium and Luxembourg
Day after Ascension Day-Belgian Defence
Whit Monday-Belgium and Luxembourg
National Holiday23 JUNLuxembourg
National Holiday21 JULBelgium
Assumption Day15 AUGBelgium and Luxembourg
All Saints Day01 NOVBelgium and Luxembourg
All Souls Day02 NOVBelgium(*)
Armistice Day11 NOVBelgium
Dynasty Day15 NOVBelgium(*)
Christmas Day25 DECBelgium and Luxembourg
Boxing Day26 DECBelgium(*) and Luxembourg
Holiday period27 - 31 DECBelgian Defence
(*) Public services only

Note: Additional military closing days will be announced by SUP.