Due to the reduction in pressure sensing accuracy of barometric altimeters with increasing altitude, there was a need above a certain flight level (FL) to increase the prescribed vertical separation minimum (VSM) of 300m (1000ft). In 1966, an increased VSM of 600m (2000ft) was established above FL290 on a global basis. ICAO provisions stated that a reduced VSM could be applied under specified conditions within designated portions of airspace on the basis of regional air navigation agreement. In 1982, ICAO and worldwide navigation office started a study about the feasibility of a reduction of the Vertical Separation Minima (VSM) above FL290 from 2000 feet to 1000 feet.
The principal benefits of the reduced VSM were:
- A theoretical doubling of the airspace capacity above FL290
- The opportunity for aircraft to operate at closer to the optimum flight level (fuel economy)
- Vertical separation minimum named VSM in airspace is:
- 300m or 1000ft below FL 290
- 600m or 2000ft above FL 290
Except where, on the basis of regional agreement, a value of less than 600m (2000ft) but not less than 300m (1000 ft) is prescribed for use by aircraft operating above FL290 within designated portions of the airspace.
RVSM was implemented to reduce the vertical separation above flight level (FL) 290 from 2000-ft minimum to 1000-ft minimum. It allows aircraft to safely fly more optimum profiles, gain fuel savings and increase airspace capacity. The process of safely changing the separation standard required a study to assess the actual performance of airspace users under the old vertical separation standard of 2000-ft and potential performance under the new standard 1000-ft. In 1988, the ICAO Review of General Concept of Separation Panel (RGCSP) completed this study and concluded that safe implementation of the 1000-ft separation standard was technically feasible. RVSM was subsequently implemented and today RVSM represents a global standard for 1000-ft vertical separation.
The reduced vertical separation minimum named RVSM is the reduction of the vertical separation minimum to 300m or 1000ft between FL290 and FL410:
- 300m or 1000ft below FL410
- 600m or 2000ftabove FL410
Flight crew indicates RVSM approval by filing a “W” in field 10 of the ICAO model flight plan.
An aircraft shall not fly on an altitude based on the reduced vertical separation minimum (RVSM) unless that minimum is approved by the national regulation in the flied airspace (RVSM Approval). After 2011, nearly all worldwide airspace has chosen RVSM including China, Russia and Africa.
An operator shall ensure that aeroplane operated in RVSM airspace is equipped with:
- Two independent altitude measurement systems (altimeter)
- An altitude alerting system (GPWS)
- An automatic altitude control system
- A secondary surveillance radar (SSR) transponder with altitude reporting system that can be connected to the altitude measurement system in use for altitude keeping
Within RVSM airspace (between FL290 and FL410 inclusive), the vertical separation minimum is 1000ft (300m) between RVSM approved aircraft. But, we have also in the world some non-RVSM approved aircrafts. These aircrafts can be state aircrafts, military aircrafts and vintage aircrafts (DC6, DC7, B707). Within RVSM airspace, the vertical separation minimum is 2000ft (600m) between non-RVSM aircraft operating as general air traffic (GAT) and any other aircraft within RVSM airspace. There is no exemption for state aircraft to operate as GAT within RVSM airspace with a 1000ft vertical separation minimum without an RVSM approval. State aircraft which are exempted from having to meet the RVSM Minimum Aircraft System Performance Specification (MASPS) shall request special handling by filling “STS/ NONRVSM”in Field 18 of the ICAO flight plan. Formation flights are to be considered non-RVSM compliant and are not permitted within RVSM airspace with a 1000 ft vertical separation minimum.
Flight crew shall indicate RVSM approval flight by filing a “W” in field 10 of the ICAO model flight plan (equipment). It is a violation of ICAO procedures for a non-approved aircraft to file a W. An important element of the certification process is the confirmation of the aircraft height keeping performance across the entire operational flight envelope. Flight crews must be trained in appropriate procedures in RVSM airspace. The flight envelope covers all combinations of speed, altitude and weight/atmospheric pressure ratio that the aircraft would expect to operate across in RVSM airspace. The pilots shall notify ATC of any equipment failure, weather hazards such as severe turbulence etc., which may affect the ability to maintain the cleared level or the RVSM requirements.
When an aircraft operating in RVSM Airspace encounters severe turbulence due to weather or wake vortex which the pilot believes will impact the aircraft’s capability to maintain its cleared flight level, the pilot shall inform the ATC. The ATC is required to establish either an appropriate horizontal separation minimum, or an increased vertical separation minimum of 2000ft.
Where a meteorological forecast is predicting severe turbulence within the RVSM Airspace, the ATC shall determine whether RVSM should be suspended, and, if so, the period of time, and specific flight level(s) and/or area. When notified by ATC of an assigned altitude deviation of more than 300ft (90 m), the pilot shall take action to return to the cleared level as quickly as possible.
