Heathrow arrival stacks
Coordinates: Inbound aircraft to London Heathrow Airport typically follow one of four Standard Arrival Routes (STARs). The STARs each terminate at a different radio beacon or RNAV waypoint, and these also define four "stacks" where aircraft can be 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 invisible helter skelters in the sky. Each stack descends in 1000 ft (300 m) intervals from 16,000 ft (4,000m) down to 8000 ft (2,100m). Aircraft hold between 7,000 feet and 15,000 feet at 1,000 foot intervals. If these holds become full, aircraft are held at more distant points before being cleared onward to one of the four main holds.
The Bovingdon stack (BNN) is for arrivals from the north west. It extends above the village of Bovingdon and the town of Chesham, and requires the VOR navigational beacon BNN which is situated on the former RAF Bovingdon airfield.
The Biggin Hill stack (BIG) on the south east edge of Greater London is for arrivals from the south east. In more recent times, the co-located RNAV waypoint WEALD has been designated an official replacement when the Biggin Hill VOR is unserviceable.
The Lambourne stack (LAM) in Essex is for arrivals from the north east.
The Ockham stack (OCK) in Surrey is for arrivals from the south west.
On 1 December 2003 at 6am, a major disaster in the stack was narrowly avoided. 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 (or stack) already occupied by a similar British Airways plane. The two planes, carrying 500 passengers, flew within 600 vertical feet (180 m) of each other.
- "ATCO: Day in the life (a real life transcript of air traffic control in the area)". Archived from the original on 29 February 2008. Retrieved 2004-11-10. CS1 maint: discouraged parameter (link) CS1 maint: bot: original URL status unknown (link)