As a passenger on a plane coming into land, do you ever get a sense of déjà vu?
You’re excited to have your feet back on solid ground so you can head home or get the holiday started. But that bridge down there… you’re sure you’ve seen it before – and that tower…
No, this isn’t Groundhog Day. What you’re experiencing is called Holding – a common practice where aircraft circle within a specified area before landing.
For air traffic controllers (ATCOs), holds are a standard procedure for managing traffic flow into an airport and maintaining safe separation between aircraft. These racetrack-shaped flight patterns allow aircraft to be held at different altitudes while the pilot awaits further instructions from air traffic control (ATC).
Holds are particularly important at airports with high traffic volumes to help maintain a safe and efficient landing sequence. They’re not exclusively used at busy airports or during peak hours but also for various operational reasons, such as weather conditions or runway changes.
Racetracks and stacks
In a hold, aircraft are “stacked” at different altitudes above a fixed point. Aircraft typically enter at the top of the hold, usually around 15,000ft, and leave from the base at around 7,000ft. With levels normally vertically separated by 1,000ft, this means up to eight aircraft can potentially hold at any one time.
ATC instructs the pilot what level to enter the hold at, when to descend to the next level and when to leave the hold to continue their approach to land.
Location is everything
Holds are positioned as part of the overall airspace design around an airport. Major airports typically have multiple holds. Heathrow Airport, for example, has four permanent holds, while Manchester Airport has three. Stansted and Luton shared two holds until an airspace change three years ago created a dedicated hold for Luton, improving efficiency for both airports.
The position of each hold is defined around a “holding fix” – a fixed point in the airspace – and published in official aviation documentation which sets out location, structure and operating requirements.
Historically, these fixes have relied on ground-based beacons for navigation, but these older technologies are being phased out as modern satellite-based waypoints and advanced onboard navigation systems make navigation far more precise.
What’s the hold up?
One of the most common reasons for holding is a high number of flights arriving at the same time. Holds allow ATCOs to organise arriving aircraft into a safe and efficient landing sequence.
Weather can also play a role. Fog, low cloud or strong winds can reduce the rate at which aircraft can safely land and holding can help controllers manage the flow of arrivals while that reduced capacity at the airport is in place.
There are also operational factors to consider. For example, an aircraft ahead may take longer than expected to land or vacate the runway, or there may be temporary restrictions or runway changes at the airport which affect how it is operating.
The future of holds
UK airspace modernisation will further reduce the need for aircraft to hold by making flight paths more efficient and predictable, while introducing advanced tools such as Intelligent Approach to improve the sequencing of arriving aircraft. Together, these improvements help ensure fewer aircraft arrive at the same time and need to wait for a landing slot.
This is made possible by a network-wide airspace design approach, supported by new technologies that allow traffic flows to be managed more holistically. By spacing aircraft more efficiently earlier in their journey, there is less need to stack aircraft in holds close to arrival airports.
Holds will remain an essential tool for managing incoming air traffic safely, particularly when demand is high or weather rolls in. The intent is to use holds more strategically, a crucial tool within a smarter airspace system.
