CAA Announces Consultation On Change To UK Airspace Transition Altitude

At lower levels, it is important for a pilot to know the vertical distance from the ground in order to ensure safe separation from terrain and other obstacles. This requires aircraft to use a local pressure setting to derive their altitude above mean sea level. At higher levels terrain avoidance becomes less of an issue, but ensuring that aircraft use the same pressure to calculate their height over large areas of airspace is critical in ensuring the safe separation of aircraft.

The Transition Altitude is the height at which aircraft change between these two pressure settings by operating their altimeter (which tells the aircrew the height of the aircraft) from reference to an altitude derived from a local pressure setting, expressed in feet (normally above mean sea level), to an area-wide standard pressure setting that allows higher level flights to be conducted using an internationally agreed set of Flight Levels.

The Transition Altitude is not currently consistent across the UK and varies between 3,000 ft and 6,000ft depending on location and type of airspace. This was set in the 1950s when aircraft instrumentation and air traffic control systems were much less accurate and aircraft performance was lower. Modern commercial aircraft reach these sorts of altitudes within seconds of departure, and the change in operating techniques as the aircraft passes through the Transition Altitude adds to the complexity and workload for pilots at a critical stage of the flight.

Also, for pilots of most light General Aviation aircraft, there will be one less pressure setting to have to consider. This will assist in the drive to reduce airspace infringements, where an aircraft enters controlled airspace without warning or permission, as confusion over which setting to use, and therefore the indicated height of the aircraft, has led to pilots being higher than they believed and aircraft infringing lower levels of controlled airspace. As such there is a safety benefit to be derived from the proposed changes both inside and outside controlled airspace.

The proposal has been developed in consultation with NATS, which manages the UKs en-route airspace, and is being managed through a joint project which includes CAA, NATS, Ministry of Defence and pilot representation. The Ministry of Defence and Irish Air Corp have indicated their support for the change in principle.

This will be a major change for air traffic controllers and their supporting systems, as well as the aviation community.

The intention is to deliver the change in conjunction with the Irish Aviation Authority (IAA) in order to significantly raise and harmonise the Transition Altitude over UK and Irish airspace within the UK / Ireland Functional Airspace Block, with the overall aim of achieving a greater commonality with other neighbouring States airspace as part of a wider aspiration to harmonise European airspace.

This change to the Transition Altitude is a key for enabling future environmental, efficiency and capacity gains by allowing the simplification and modernisation of the UKs airspace system as proposed by the CAAs Future Airspace Strategy*. NATS is already working to modernise the UKs airspace, by developing more environmentally efficient procedures such as continuous climbs and descents. These future changes are dependent on the new Transition Altitude.

The consultation runs until 1 May 2012 and is available at: www.caa.co.uk/default.aspx?catid=1350&pagetype=90&pageid=12919

Subject to the outcome of the consultation and the possibility of a further round of consultation, the proposed timescale for implementation of the new Transition Altitude is the winter of 2013/14.