Editing Heathrow arrival stacks (section)

{{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.