Is this the end of stack holding?

Choosing the optimum combination of arrivals, based on the separation between arriving aircraft pairs, is the key to making the most of available runway capacity. For many airports in Asia Pacific that are already operating above capacity, having a constant stream of arrivals allows optimum sequencing to take place and is absolutely vital to the smooth running of the operation.

It will be many years before aircraft can arrive at an airport ‘just in time’ so in the meantime, there is a need for a slight oversupply of aircraft to ensure that runway capacity is not wasted with unnecessary gaps. Holding stacks are incredibly useful in achieving this. However, they are noisy, inflexible and mean aircraft burn more fuel at lower levels and emit more CO2.

With the advent of more sophisticated satellite based navigation systems it is now possible for aircraft to follow routes with an incredible level of accuracy. That means we’re able to be smarter about airport arrivals using a concept called Linear Holding.

How a traditional stack hold compares to linear holds (click to enlarge)

There are two different types of linear hold, the trombone and the point merge. Both work by keeping all the arriving aircraft at the same level, but separated in the horizontal plane by satellite navigation tracks. At exactly the right moment – to the second – the aircraft is vectored off the linear hold and onto final approach. The big difference is that these linear holds can be much higher than a traditional stack, potentially up to 20,000 feet, and are therefore quieter for people living underneath and more fuel efficient for the airlines.

The traditional stack holds would remain for use in exceptional circumstances but they would be moved further out and raised up.

NATS has already introduced one linear in the UK; with the implementation of a point merge hold for arrivals into London City Airport. Instead of flying over land, arrivals now join the point merge arc out over the North Sea before being peeled off in the optimum order for a continuous decent approach into the airport.

Linear holds could help airports in Asia Pacific keep pace with rising demand while at the same time work to take advantage of the technologies that can help us minimise the impact of noise on the ground.