1.1 The table of units of measurement used in the United Kingdom is that which is published in ICAO Annex 5 (Fifth Edition) Chapter 3 including permitted non-SI alternative units.

Measurement of	Units
Distance used in navigation, position report etc – generally in excess of 2 or 3 nautical miles	*Nautical miles and tenths
Relatively short distances such as those relating to aerodromes (eg runway lengths)	Metres
Altitudes, elevations and heights	Feet and Flight Levels
Horizontal speed including wind speed	Knots
Vertical speed	Feet per minute
Wind direction for landing and taking off	Degrees Magnetic
Wind direction except for landing and taking off	Degrees True
Visibility < 5000 metres (including RVR)	Metres
Visibility > 5000 metres	Kilometres
Distance from cloud	Metres
Depth of runway deposit	Centimetres or millimetres
Altimeter setting	Hectopascals
Temperature	Degrees Celsius (Centigrade)
Weight/mass	Metric tonnes or kilogrammes
Date/Time	Year, Month, Day, Hour and Minute, the day of 24 hours beginning at midnight Co-ordinated Universal Time
* International nautical miles, for which conversion into metres is given by 1 international nautical mile = 1852 M.

1.2 There is no sharp dividing line between the usage of nautical miles or metres for the two types of horizontal distances referred to in the table above. There is no hard and fast rule, but distances having a navigational or position reporting aspect are given in nautical miles even if they are less than 2 nautical miles (eg ranges from touchdown during a precision approach). These are given in nautical miles and fractions. Distances on the aerodrome (eg runway lengths, etc.) are given in metres. Distances from obstacles in the vicinity of aerodromes and ILS marker distances are generally shown in nautical miles and tenths, except when it is necessary for greater accuracy for some middle markers to be shown in metres.

1.3 Nautical miles or feet, as appropriate, will be used in designating horizontal distances at military aerodromes, joint-user aerodromes controlled by Service personnel and in RAF Sections at Air Traffic Control Centres. Horizontal distances will, however, be given to civil pilots in metric units, on request. Similarly, at civil aerodromes, joint-user aerodromes under civil control and in civil sections at Air Traffic Control Centres, Service pilots will be given distances in nautical miles or feet, as appropriate, on request.

2.1 The Gregorian calendar and Coordinated Universal Time (UTC) shall be used as the temporal reference system for air navigation.

2.2 Daylight saving time is UTC plus 1 hour. The expression “summer period” indicates that part of the year in which “daylight saving time” is in force. The other part of the year is named the “winter period”. Times applicable during the “summer period” are given in brackets.

2.3 The “summer period” is introduced every year on the last Sunday in MAR at 01:00 UTC and ceases on the last Sunday in OCT at 01:00 UTC.

2.4 Guidance material for expressing time periods in AIS Products is available on the NATS AIS website www.nats.aero/ais.

3.1 The geographical co-ordinates indicating Latitude and Longitude are expressed in terms of the World Geodetic System of 1984 (WGS84) geodetic reference datum.

3.2 Surveyed co-ordinates WGS84 are realised in the UK using the National GPS Network, a 3-D TRF (Terrestrial Reference Frame), using the ETRS89 (European Terrain Reference System 89) datum or by direct connection to the IGS system.

3.3 Area of Application

3.4 Aerodromes with coordinates which have been transformed into WGS84 coordinates but whose accuracy of original field work does not meet the requirements in Annex 11, Chapter 2, and Annex 14, Volumes I and II, Chapter 2, are listed below:

Cheltenham
Derby

4.1 The Ordnance Datum Newlyn (ODN) can be considered the source of Mean Sea Level (MSL) in the UK.

4.2 OSGM15 is the National Geoid Model used in the UK for determining elevations Above Mean Sea Level (AMSL) datum.

4.3 Primary term expressed in UK AIP.

1. Elevation (ELEV) - The vertical distance measured from Mean Sea Level (MSL). (FT/M)

4.4 Other terms expressed in AIP:

1. Above Aerodrome Level (AAL) - The vertical distance measured from a specified aerodrome. (FT/M)

2. Above Ground Level (AGL) - The vertical distance measured from the surface of the earth. (FT/M)

3. Above Mean Sea Level (AMSL) - The vertical distance measured from Mean Sea Level (MSL). (FT/M)

4. Altitude (ALT) - The vertical distance measured from Mean Sea Level (MSL). (FT/M)

5. Flight Level (FL) - A surface of constant atmosphere pressure which is related to a specific pressure datum, 1013.2 hPa, and is separated from other such surfaces by specific pressure intervals. Altitude above sea level in 100 FT units measured according to a standard atmosphere. Only above the transition level are flight levels used to indicate altitude; below the transition level feet (FT) are used.
   e.g. FL250 = 25,000 FT AMSL when the pressure at sea level is 1013.2 hPa.

6. Height (HGT) - The vertical distance measured from a specified point or datum. e.g. An aerodrome.

7. Surface (SFC) - The distance measured from the surface of the earth. (FT/M)

5.1 The nationality mark for British Civil aircraft is the letter 'G'. This nationality mark is followed by a hyphen and a registration mark consisting of four letters. Example: G-BAAA.

6.1 The following link provides access to the government website announcing public holidays for the UK:

https://www.gov.uk/bank-holidays