Reduced Vertical Separation Minima or Minimum (RVSM) is an aviation term used to describe the reduction of the standard vertical separation required between aircraft flying above FL285 (28,500 ft.) and up to FL410 (41,000 ft.) from 2,000 feet to 1,000 feet (or between 8,900 metres and 12,500 metres from 600 metres to 300 metres). This therefore increases the number of aircraft that can safely fly in a particular volume of airspace.
Historically, standard vertical separation was 1,000 feet from the surface to FL290, 2,000 feet from FL290 to FL410 and 4,000 feet above this. This was because the accuracy of the pressure altimeter (used to determine altitude) decreases with height. Over time, Air data computers (ADCs) combined with altimeters have become more accurate and autopilots more adept at maintaining a set level, therefore it became apparent that for many modern aircraft, the 2,000 feet separation was too cautious. It was therefore proposed by ICAO that this be reduced to 1,000 feet.
In the US this program was known as the Domestic Reduced Vertical Separation Minimum (DRVSM).
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Between 1997 and 2005 RVSM was implemented in all of Europe, North Africa, Southeast Asia and North America, South America, and over the North Atlantic, South Atlantic, and Pacific Oceans. The North Atlantic implemented initially in March 1997 at flight levels 330 through 370. The entire western hemisphere implemented RVSM FL290-FL410 on January 20, 2005. Africa implemented it on September 25, 2008.
Russian Federation implemented RVSM and Flight Levels in feet on November 17th 2011. Below transition level, meters are still in use however.
Only aircraft with specially certified altimeters and autopilots may fly in RVSM airspace, otherwise the aircraft must fly lower or higher than the airspace, or seek special exemption from the requirements. Additionally, aircraft operators (airlines or corporate operators) must receive specific approval from the aircraft's state of registry in order to conduct operations in RVSM airspace. Non RVSM approved aircraft may transit through RVSM airspace provided they are given continuous climb throughout the designated airspace, and 2,000 ft vertical separation is provided at all times between the non-RVSM flight, and all others for the duration of the climb/descent.
"State aircraft", which includes military, customs and police aircraft, are exempted from the requirement to be RVSM approved. Participating states have been requested, however, to adapt their State aircraft for RVSM approval, to the extent possible, and especially those aircraft used for General Air Traffic (GAT).[1]