Reduced vertical separation minimum ( RVSM ) is the reduction, from 2,000 feet to 1,000 feet, of the standard vertical separation required between aircraft flying between flight level 290 (29,000 ft ) and flight level 410 (41,000 ft). Expressed in the International System of Units (SI), it is the reduction, from 600 m to 300 m, of required vertical separation of aircraft between altitudes 8,850 and 12,500 m. This reduction in vertical separation minimum therefore increases the number of aircraft that can fly in a particular volume of controlled airspace .
20-405: In the 1940s (original ICAO regulations), standard separation was 1000 feet except in specific circumstances, when it was 500 feet. In 1958 the standard vertical separation of aircraft in controlled airspace was set at 1,000 feet from ground level or sea level to flight level 290, and at 2,000 feet above flight level 290. The larger minimum separation at higher altitudes was necessary because
40-415: A GPS receiver), or height above average terrain (AAT or HAAT, in broadcast engineering ). In other words, these expressions (AGL, AMSL, HAE, AAT) indicate where the "zero level" or "reference altitude" – the vertical datum – is located. A pilot flying an aircraft under instrument flight rules (typically under poor visibility conditions) must rely on the aircraft's altimeter to decide when to deploy
60-411: A feature of the terrain itself in terms of distance above MSL. In weather and climate studies, measurements or simulations often need to refer to a specific height or altitude, which is naturally AGL. However, the values of geophysical variables measured in various places on the natural (ground) surface may not be easily compared in hilly or mountainous terrain, because part of the observed variability
80-498: Is common to provide uncontrolled airspace in areas where significant air transport or military activity is not expected. The International Civil Aviation Organization divides airspace into seven classes, from A to G , in order of decreasing ATC regulation of flights. Classes A to E are controlled airspace. Flight under instrument flight rules (IFR) is allowed in all controlled airspace. Some countries also permit IFR in uncontrolled airspace). Flight under visual flight rules (VFR)
100-399: Is due to changes in the altitude of the surface. For this reason, variables such as pressure or temperature are sometimes 'reduced' to mean sea level. In general circulation models and global climate models , the state and properties of the atmosphere are specified or computed at a number of discrete locations and heights. When the topography of the continents is explicitly represented,
120-446: Is height referencing the highest point on the airfield, TDZE (touchdown zone elevation) or TH (threshold height) which both refer to the elevation of the landing end of the runway measured AMSL and AGL respectively. In general, "altitude" refers to distance above mean sea level (MSL or AMSL), "height" refers to distance above a particular point (e.g. the airport, runway threshold , or ground at present location), and "elevation" describes
140-464: Is permitted in all airspace except class A. This aviation -related article is a stub . You can help Misplaced Pages by expanding it . Above Ground Level In aviation , atmospheric sciences and broadcasting , a height above ground level ( AGL or HAGL ) is a height measured with respect to the underlying ground surface . This is as opposed to height above mean sea level (AMSL or HAMSL), height above ellipsoid (HAE, as reported by
160-483: Is the opposite of uncontrolled airspace . Controlled airspace is established mainly for three different reasons: Controlled airspace usually exists in the immediate vicinity of busier airports, where aircraft used in commercial air transport flights are climbing out from or making an approach to the airport, or at higher levels where air transport flights would tend to cruise. Some countries also provide controlled airspace almost generally, however in most countries it
180-532: 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. However, in some FIRs, meters are still in use below transition level . 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
200-425: The broadcast range of a station. Rather, it is HAAT (the height above the average terrain (in the surrounding area)) which is used to determine how far a broadcast station (or any other sort of VHF or higher radio-frequency ) transmission will travel. From aviation safety perspective though, the more important aspect is the height of the radio tower used to support the radio antenna . In this case, height AGL
220-415: The undercarriage and prepare for landing. Therefore, the pilot needs reliable information on the height of the plane with respect to the landing area (usually an airport). The altimeter, which is usually a barometer calibrated in units of distance instead of atmospheric pressure , can therefore be set in such a way as to indicate the height of the aircraft above ground. This is done by communicating with
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#1732791569634240-449: The RVSM level is exceeded it is an 'incident' and needs to be reported within 72 hours. Equipment Requirements: Controlled airspace Controlled airspace is airspace of defined dimensions within which air traffic control (ATC) services are provided. The level of control varies with different classes of airspace . Controlled airspace usually imposes higher weather minimums than are applicable in uncontrolled airspace. It
260-401: The accuracy of altimeters , used to determine altitude by measuring air pressure, decreases with height. Efforts to reduce this separation above flight level 290 began almost immediately, but doing so without compromising safety required improvements in altimeters and other equipment, due in part to inherent difficulties in accurately determining and maintaining aircraft altitudes and, therefore,
280-477: The actual vertical distance between aircraft. It was not until the 1990s that air data computers (ADCs), altimeters, and autopilot systems became sufficiently accurate to safely reduce the vertical separation minimum. Thus, RVSM in effect constituted a return to the original procedures established in the mid-1940s, with the notable difference that 500 feet separation is only permitted between IFR and VFR flights (on non-converging tracks). Between 1997 and 2005 RVSM
300-423: The altitudes of these locations are set above the simulated ground level. This is often implemented using the so-called sigma coordinate system, which is the ratio of the pressure at a location (latitude, longitude, altitude) divided by the pressure at the nadir of that location on ground surface (same latitude, same longitude, altitude AGL = 0). In broadcasting, altitude AGL has relatively little direct bearing on
320-413: The control tower of the airport (to get the current surface pressure) and setting the altimeter so as to read zero on the ground of that airport. Confusion between AGL and AMSL, or improper calibration of the altimeter, may result in controlled flight into terrain , a crash of a fully functioning aircraft under pilot control. While the use of a barometric altimeter setting that provides a zero reading on
340-535: The ground of the airport is a reference available to pilots, in commercial aviation it is a country-specific procedure that is not often used (it is used, e.g., in Russia, and a few other countries ). Most countries (Far East, North and South America, all of Europe, Africa, Australia) use the airport's AMSL (above mean sea level) elevation as a reference. During approaches to landing, there are several other references that are used, including AFE (above field elevation) which
360-414: The non-RVSM flight, and all others for the duration of the climb/descent. "State aircraft", which includes aircraft used in military, customs and police service, 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). If
380-411: The requirements. Additionally, aircraft operators (airlines or corporate operators) must receive specific approval from the aircraft's state of registry to conduct operations in RVSM airspace. Non RVSM approved aircraft may transit through RVSM airspace provided they are given continuous climb/descent throughout the designated airspace, and 2,000 ft vertical separation is provided at all times between
400-592: 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
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