RVSM

Reduced vertical separation minima or minimum (RVSM) is the reduction of the standard vertical separation required between aircraft flying between FL290 (29,000 ft) and FL410 (41,000 ft) inclusive, from 2,000 feet to 1,000 feet (or between 8,850 and 12,500 m from 600 m to 300 m). This therefore increases the number of aircraft that can safely fly in a particular volume of airspace.

In 1958 the standard vertical separation was set to 1,000 feet from the surface to FL290, and 2,000 feet above FL290. This was because the accuracy of the pressure altimeter (used to determine altitude) decreases with height. Work on reducing this to 1,000 feet at all levels began almost immediately, but it was not until the 1990s that air data computers (ADCs), altimeters and autopilots became sufficiently accurate to make this a reality.

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.

The People's Republic of China implemented metric RVSM on 21 November 2007. But the Hong Kong FIR continued to use flight levels in feet.

The Russian Federation implemented RVSM and flight levels in feet on November 17, 2011. Below transition level, however, meters are still in use.

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.

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