With effect from 27 March 1997, the first phase of reduced vertical separation minimum (RVSM) was implemented in the North Atlantic minimum navigation performance specifications (MNPS) airspace, in accordance with regional supplementary procedures approved by Council. This enables RVSM-approved aircraft, between flight level 290 and 410 inclusive, to operate with 1 000 ft vertical separation instead of 2 000 ft, as was previously required. Height-keeping performance needs to be demonstrated as part of the RVSM approval process, and is being monitored on an on-going basis by the Central Monitoring Agency on behalf of the North Atlantic Systems Planning Group (NAT SPG). RVSM almost doubles the airspace capacity in the flight level band concerned. The new system is being financed under a new joint financing arrangement inspired by the experience of the Danish and Icelandic Joint Financing Agreements.Under the arrangement, Canada, Iceland, Ireland, Portugal and the United Kingdom fund and own the facilities for a height monitoring project on the basis of their share of the North Atlantic traffic. The United States obligations include the provision of GMU equipment, a number of reference stations and post-processing equipment. Operational, maintenance and depreciation costs, as well as ICAO's administrative costs, are met through user charges. As with the Danish and Icelandic Joint Financing Agreements, the United Kingdom Civil Aviation Authority serves as billing and collecting agent.