This website provides an overview of the status of 8.33 kHz channel spacing above FL195 as well as information on the on-going initiative to apply 8.33 kHz channel spacing below FL195.
Radio communication systems for aircraft are used primarily for the purpose of air traffic control (ATC). Communications for air traffic control use the Very High Frequency (VHF) band between 118 and 137 MHz. The same frequency can be reassigned many times provided that there are no interference problems.
Increases in air traffic levels led to an increase in the demand for operational improvements like re-sectorisation which have in turn have led to an increase in the demand for VHF assignments.
The number of available VHF assignments was increased by optimising frequency re-use (improved coordination and possibly confining VHF assignments to smaller areas), using more spectrum (118 to 136 MHz increased to 137 MHz), and splitting the radio spectrum into narrower band widths (50 kHz to 25 kHz channels)
In 1994 it was decided to introduce a further channel split from 25 to 8.33 kHz. Subsequently, 8.33 kHz was introduced above FL245 in the ICAO EUR Region from October 1999 and above FL195 from the 15 March 2007. At the time of writing, 8.33 kHz channels have been implemented in the airspace of over 20 ICAO EUR Region States. On 16 November 2012 it was agreed to further extend 8.33 kHz to all european airspace by 2018.