News Item

UK to drop millibars

UK aviation is to drop the use of 'millibars' when referring to atmospheric pressure - are other activities to follow suit?

The UK currently uses the millibar (mb) as the unit of measurement for atmospheric pressure - but ICAO defines the hectopascal (hPa) for this purpose.

Moreover, a EC Regulation states that meteorological and air traffic services (ATS) should comply with the ICAO requiresment - the use of hPa is already in use in flight information regions (FIRs) adjoining the UK.

But this week has seen the CAA publish an Information Notice (IN) to notify the adoption of the hPa as the unit of measurement for atmospheric pressure within the UK from 17 November 2011.

Luckily, the millibar is directly equivalent to the hectopascal, so no conversion factor is required - the only difference is in nomenclature. And the EC Regulation permits aircraft altimeter subscales to be calibrated in mb or hPa - catering for legacy altimeters.

But from 0001Z on 17 November, 'hectopascal' is to be used in radio conversations and meteorological reports and forecasts in UK - and no spoken abbreviation will be permitted.

A question to the Met Office - asking whether this will apply in other walks of life - has yet to be answered.

Details from the CAA below.

  • 04 June 2011
  • CMAG

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