Editing Heathrow arrival stacks

{{Short description|Air traffic control mechanism}}
{{Use dmy dates|date=October 2021}}
{{Use British English|date=May 2013}}
{{coord|51.726101|N|0.549722|W|display=title}}
Inbound aircraft to London [[Heathrow Airport]] typically follow one of a number of [[Standard terminal arrival route|Standard Terminal Arrival Routes]] (STARs). The STARs each terminate at one of four different [[RNAV]] waypoints (co-located with [[VHF omnidirectional range|VOR]] navigational aids), and these also define four "stacks"<ref name="UK AIP">{{cite web|url=https://www.aurora.nats.co.uk/htmlAIP/Publications/2021-10-07-AIRAC/html/index-en-GB.html|title=UK AIP - EGLL London Heathrow|publisher=NATS|access-date=1 November 2021|author=NATS|date=17 October 2021 }}</ref> where aircraft can be [[Holding (aviation)|held]], if necessary, until they are cleared to begin their approach to land.  Stacks are sections of [[airspace]] where inbound aircraft will normally use the pattern closest to their arrival route. They can be visualised as an invisible [[helix]] in the sky. Each stack descends in {{convert|1000|ft|m|0}} intervals from {{convert|16,000|ft|m|0}} down to {{convert|8000|ft|m|0}}. If these holds become full, aircraft are held at more distant points before being cleared onward to one of the four main holds.

==The stacks==
===Bovingdon===
The Bovingdon stack is for arrivals from the north west. It extends above the village of [[Bovingdon]] and the town of [[Chesham]], and uses the RNAV waypoint BNN (co-located with the BNN VOR), which is situated on the former [[RAF Bovingdon]] airfield.

===Biggin Hill===
The [[Biggin Hill]] stack on the south east edge of Greater London is for arrivals from the south east.  It uses the RNAV waypoint BIG (co-located with the BIG VOR), which is situated on [[London Biggin Hill Airport]].

===Lambourne===
The [[Lambourne]] stack in Essex is for arrivals from the north east.  It uses the RNAV waypoint LAM (co-located with the LAM VOR), which is situated adjacent to [[Stapleford Aerodrome]].

===Ockham===

The [[Ockham, Surrey|Ockham]] stack in Surrey is for arrivals from the south west.  It uses the RNAV waypoint OCK (co-located with the OCK VOR), which is situated on the former [[Wisley Airfield]]. During typical easterly operations, the proximity of arrival traffic via OCK requires departures from Heathrow's runway 09R towards the Compton VOR (CPT) to follow a non-standard departure procedure.

==Developments==
The arrival procedures are being revised since 2014 to reduce stacking by introducing variable speed limits<ref>{{cite web |last1=Paton |first1=Graeme |title=Speed limit stops aircraft stacking up over Heathrow |url=https://www.thetimes.com/travel/advice/speed-limit-stops-aircraft-stacking-up-over-heathrow-dlmrfqdtf |website=[[The Times]] |archive-url=https://archive.today/20230101103504/https://www.thetimes.co.uk/article/speed-limit-stops-aircraft-stacking-up-over-heathrow-dlmrfqdtf |archive-date=1 January 2023|date=25 November 2016 |url-status=live}}</ref> and alternative holding procedures.<ref>{{cite web |last1=Curtis |first1=Dave |title=Is this the end of stack holding? |url=https://nats.aero/blog/2016/05/is-this-the-end-of-stack-holding/ |website=NATS Blog |date=20 May 2016}}</ref>

==Incidents==
At 6&nbsp;am on 1 December 2003, a major disaster in the stack was narrowly avoided when two planes, carrying a total of 500 passengers, flew within {{convert|600|ft}} of vertical clearance. An [[air traffic controller]] was blamed by a later inquiry for misdirecting traffic when he ordered a [[United Airlines]] [[Boeing 777]] into a level of the Bovingdon Hold already occupied by a similar [[British Airways]] aircraft.<ref>{{cite web |last1=Webster |first1=Ben |title=Radar flaw sent planes just 600ft from disaster |url=https://www.thetimes.com/article/radar-flaw-sent-planes-just-600ft-from-disaster-bzqrt6drvdf |website=[[The Times]] |date=22 October 2004 |accessdate=27 June 2024}}</ref>

==References==
<references />

==Further reading==
* Howell, G. (1976). [https://www.cambridge.org/core/journals/aeronautical-journal/article/abs/future-system-consideration-for-operations-of-aircraft-in-the-terminal-movement-area/FE1DA8500AEB8E48F23730F29D53AC94 Future system consideration for operations of aircraft in the terminal movement area]. ''The Aeronautical Journal'', 80(782), 51–60. doi:10.1017/S0001924000033480
* {{cite web |last1=Millward |first1=David |title=More than half of Heathrow flights forced to circle before landing |url=https://www.telegraph.co.uk/travel/news/More-than-half-of-Heathrow-flights-forced-to-circle-before-landing/ |website=The Telegraph |date=5 February 2016}}
* {{cite web |title=End stacking of aircraft over airport, says MP |url=https://www.henleystandard.co.uk/news/home/133453/end-stacking-of-aircraft-over-airport-says-mp.html |website=Henley Standard|date=27 November 2018}}

==External links==
*{{cite web|url=http://avsim.com/atco/dayinthelife.htm |title=ATCO: Day in the life (a real life transcript of air traffic control in the area) |accessdate=2004-11-10 |url-status=bot: unknown |archiveurl=https://web.archive.org/web/20080229134124/http://avsim.com/atco/dayinthelife.htm |archivedate=29 February 2008 }}
*[https://www.youtube.com/watch?v=_jr6Ly7RBZg London 24 - Layers of London air traffic], [[NATS Holdings|NATS]], 2014

[[Category:Air traffic control in the United Kingdom]]
[[Category:Aviation in London]]
[[Category:Aviation in England]]
[[Category:Heathrow Airport]]