View source for Reduced vertical separation minima

{{Short description|Height reduction of aircraft in flight}}
{{Use mdy dates|date=August 2012}}
'''Reduced vertical separation minimum''' ('''RVSM''') is the reduction, from 2,000 feet to 1,000 feet, of the standard [[vertical separation (aviation)|vertical separation]] required between aircraft flying between [[flight level]] 290 (29,000&nbsp;[[foot (unit)|ft]]) and flight level 410 (41,000&nbsp;ft). Expressed in the [[International System of Units]] (SI), it is the reduction, from 600&nbsp;[[metre|m]] to 300&nbsp;m, of required vertical separation of aircraft between altitudes 8,850&nbsp; and 12,500&nbsp;m. This reduction in vertical separation minimum therefore increases the number of aircraft that can fly in a particular volume of [[controlled airspace]].<ref>{{Cite web|url=https://www.icao.int/ESAF/Pages/rvsm-communications.aspx|title=RVSM Programme|website=www.icao.int}}</ref>
==Historical background==
In the 1940s (original ICAO regulations), standard separation was 1000 feet except in specific circumstances, when it was 500 feet.<ref>{{Cite web |title=history of rvsm |url=https://www.icao.int/esaf/documents/rvsm/2010/afi%20riss/presentations.pdf}}</ref> In 1958 the standard vertical separation of aircraft in [[controlled airspace]] was set at 1,000 [[Foot (unit)|feet]] from [[Earth's surface|ground level]] or [[sea level]] to [[flight level]] 290, and at 2,000 feet above flight level 290.<ref>Silva 2010 pp.&nbsp;7–8.</ref> The larger minimum separation at higher altitudes was necessary because the accuracy of [[altimeter]]s, used to determine altitude by measuring air pressure, decreases with height.{{Citation needed|date=March 2019}} Efforts to reduce this separation above flight level 290 began almost immediately,<ref>Silva 2010 pp.&nbsp;9–15.</ref> 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, the actual vertical distance between aircraft.<ref>Silva 2010 pp.&nbsp;18–21.</ref> It was not until the 1990s that [[air data computer]]s (ADCs), altimeters, and [[autopilot]] systems became sufficiently accurate to safely reduce the vertical separation minimum.<ref>Silva 2010 p.&nbsp;17.</ref> 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).
==Implementation==
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 Ocean]]s. 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 [[China|People's Republic of China]] implemented [[Flight level#People's Republic of China and Mongolia|metric RVSM]] on 21 November 2007.<ref>[http://www.chinarma.cn/English/flightlevelallocationscheme.html CAAC RVSM FLIGHT LEVEL ALLOCATION SCHEME on China RMA] {{webarchive |url=https://web.archive.org/web/20120106064010/http://www.chinarma.cn/English/flightlevelallocationscheme.html |date=January 6, 2012 }}</ref> But the [[Hong Kong]] [[Flight information region|FIR]] continued to use flight levels in feet.<ref>{{Cite web|url=http://www.hkatc.gov.hk/HK_AIP/AIP/GEN/HK_GEN2.1.pdf|title=Hong Kong AIP}}</ref>
The [[Russia|Russian Federation]] implemented RVSM and [[Flight level#Flight levels in Russian Federation and North Korea|flight levels in feet]] on November 17, 2011. However, in some FIRs, meters are still in use below [[Flight level#Transition altitude|transition level]].<ref>{{Cite web|date=10 December 2020|title=The New Airspace Structure over European Part of Russia|url=https://gkovd.ru/en/news/the-new-airspace-structure-over-european-part-of-russia/|access-date=2 May 2021|website=“State Air Traffic Management Corporation of the Russian Federation”}}</ref>
==Requirements==
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 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&nbsp;ft vertical separation is provided at all times between the non-RVSM flight, and all others for the duration of the climb/descent.{{citation needed|date=June 2015}}
"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 the RVSM level is exceeded it is an 'incident' and needs to be reported within 72 hours.<ref>{{cite web | url=https://regulatorylibrary.caa.co.uk/965-2012/Content/Regs/12050_SPARVSM115_RVSM_height-keeping_errors.htm | title=SPARVSM115 RVSM height-keeping errors }}</ref>
Equipment Requirements:
* Two independent altitude measuring systems
* SSR (secondary surveillance radar) altitude reporting transponder
* Altitude alert system
* Autopilot
* Flight Crew approved training program / Op Specs Approval
* No damage outside the Structural Repair Manual (SRM) limits in the RVSM critical areas{{cn|date=March 2024}}
==See also==
* [[Acronyms and abbreviations in avionics]]
* [[Aviation safety]]
* [[Flight level]]
* [[List of aviation, aerospace and aeronautical abbreviations]]
* [[North Atlantic Tracks]]
* [[Strategic lateral offset procedure]]
* [[Traffic collision avoidance system]] (TCAS)
==References==
{{reflist}}
==Further reading==
* Authorization of Aircraft and Operators for Flight in Reduced Vertical Separation Minimum (RVSM) Airspace [https://www.faa.gov/air_traffic/separation_standards/rvsm/documents/AC91_85B.pdf]
*{{cite book | url=http://www.icao.int/esaf/documents/rvsm/2010/afi%20riss/presentations.pdf | first=Saulo |last=Silva |publisher=[[International Civil Aviation Organization]] |title=A Brief History of RVSM |date=April 2010 | access-date=1 March 2019}}
==External links==
*[http://www.skybrary.aero/index.php/Altimetry_System_Error Altimetry System Error (ASE) and its effects on operations in RVSM airspace]
*[http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/enroute/rvsm/ FAA article promoting the new rule]
*[http://www.washtimes.com/commentary/20040211-093522-2346r.htm Friendlier Skies – Washington Times]
*[http://www.skybrary.aero/index.php/RVSM RVSM on Skybrary]
*[https://web.archive.org/web/20080920031147/http://www.spaceagecontrol.com/Trailing-cone Use of Trailing Cones for RVSM Certification]
[[Category:Air traffic control]]
[[Category:1997 introductions]]
[[Category:Altitudes in aviation]]