Heathrow arrival stacks are a set of organized holding patterns used to sequence inbound aircraft destined for London Heathrow Airport (LHR), one of the world’s busiest international airports. The stacks are managed by the United Kingdom’s air navigation service provider, NATS (formerly National Air Traffic Services), and are integral to the airport’s capacity and safety management, especially during periods of high traffic demand or adverse weather conditions.
Purpose and Function
When arriving aircraft approach the Heathrow terminal area, they are assigned to a specific arrival route (Standard Instrument Arrival, or STAR) that may include a holding pattern, commonly referred to as a “stack.” The stacks allow air traffic controllers to maintain safe separation between aircraft by assigning them distinct altitude levels, typically spaced at 1,000‑feet intervals. Aircraft circulate within the stack until they receive clearance to descend to the next lower level or to proceed to the final approach.
Typical Altitude Levels
The standard altitude levels for Heathrow arrival stacks are:
- Flight Level (FL) 160 (approximately 16,000 ft) – top of the stack
- FL150
- FL140
- FL130
- FL120
- FL110 – bottom of the stack
These levels may be adjusted in response to traffic density, aircraft performance, or operational considerations.
Primary Arrival Routes and Associated Stacks
Heathrow operates several arrival routes, each linked to a specific holding stack:
| Arrival Route (STAR) | Direction from Heathrow | Associated Stack |
|---|---|---|
| Northern (e.g., “Bovingdon”) | North‑west | Bovingdon stack |
| Western (e.g., “Stansted”) | West‑northwest | Stansted stack |
| Southern (e.g., “Biggin Hill”) | South‑southwest | Biggin Hill stack |
| Eastern (e.g., “Lambourne”) | East‑south‑east | Lambourne stack |
| North‑East (e.g., “Ockham”) | North‑east | Ockham stack |
Each stack is positioned at a defined waypoint located several miles from the airport, allowing a predictable pattern for aircraft to hold while awaiting sequencing clearance.
Management and Operational Procedures
- Air Traffic Control (ATC): NATS controllers monitor and manage the stacks using radar and flight data processing systems. Aircraft are instructed to “enter the stack” at a specified altitude and to “depart the stack” when cleared for further descent.
- Speed Control: Pilots are often required to fly a specific speed (typically 250 kt below 10 000 ft) to maintain spacing within the stack.
- Slot Allocation: Arrival slots, allocated by the Central Flow Management Unit (CFMU), determine when an aircraft may be cleared to leave the stack and proceed to the final approach.
- Weather and Capacity Adjustments: During low‑visibility conditions, strong winds, or runway closures, the number of aircraft permitted in a stack may be reduced, and alternative routes or holding points may be employed.
Historical Context
The use of arrival stacks at Heathrow dates back to the expansion of jet traffic in the 1960s and 1970s, when the need for systematic sequencing grew alongside increasing flight numbers. Over time, the stacks have been refined to incorporate more precise altitude spacing, better radar coverage, and advanced traffic flow management tools such as the Airport Collaborative Decision Making (A‑CDM) initiative, which aims to improve predictability and efficiency.
Safety and Performance Impact
Arrival stacks are a critical component of Heathrow’s safety record. By providing a controlled environment for aircraft to await clearance, the stacks reduce the risk of mid‑air conflicts and enable controllers to manage runway occupancy times effectively. However, excessive stacking can increase fuel burn and emissions, prompting ongoing efforts to optimize arrivals through measures such as Continuous Descent Operations (CDO) and dynamic slot scheduling.
References
- NATS. “Heathrow Arrival Management.” NATS Operational Handbook, 2023.
- Civil Aviation Authority (CAA). “Air Traffic Management – Holding Procedures.” CAA Publication No. 2022‑04.
- Heathrow Airport Ltd. “Airport Collaborative Decision Making (A‑CDM) – Arrival Procedures.” Heathrow Publications, 2022.
Note: Information reflects operational practices as of 2023 and may be subject to change with evolving air traffic management policies.