In the late 1970's, faced with rising fuel costs and growing demands for a more efficient use of the available airspace, the International Civil Aviation Organisation (ICAO) initiated a comprehensive programme of studies to examine the feasibility of reducing the 2000ft Vertical Separation Minimum (VSM) applied above FL290, to the 1000ft VSM used below FL290. Throughout the 1980s, various studies were conducted, under the auspices of ICAO, in Canada, Europe, Japan, and the USA.
The underlying approach of the programmes was to:
- Determine the height keeping accuracy of the altimetry systems of the then current aircraft population.
- Establish the causes of observed height keeping errors.
- Determine the required safety levels for the implementation and use of a Reduced Vertical Separation Minimum of 1000ft at/above FL290.
- Define a Minimum Aircraft System Performance Specification (MASPS) - for aircraft altimetry and associated height keeping equipment - which would improve height keeping accuracy to a standard compatible with the agreed safety requirements for RVSM.
- Determine whether the global implementation and use of RVSM was:
- Technically feasible, subject to the overriding need to satisfy the agreed safety standards.
- Cost beneficial.
The results of these exhaustive studies demonstrated that the global reduction of vertical separation was safe, feasible - without the imposition of unduly demanding technical requirements, and cost beneficial.
The studies also showed that the types of aircraft and the essentially unidirectional tidal flow of traffic in the North Atlantic (NAT) Minimum Navigation Performance Specification (MNPS) airspace made this Region an ideal candidate for the first implementation of RVSM.
Planning for RVSM in the NAT Region commenced in 1990. The first stage of the Operational Evaluation phase, using the 1000 ft RVSM, began on the 27th March 1997 at and between FL330 and FL370 inclusive. In 1998, the second stage extended the use of RVSM to between FL310 and FL390 inclusive.