Let’s begin from the start! The definition of holding (or flying a hold) in the aviation field means some maneuvers of the airplane before the landing. The incoming airplane should generally be stacked when an aircraft that has arrived at its destination however cannot land, thanks to the traffic jam, poor weather, or runway inaccessibility.
For those that don’t know, holding stacks are the airport’s ‘waiting rooms’ for arriving aircraft. Whenever aircraft cannot proceed to land immediately, flights enter at the top of the stack – usually at around 11 or 12 thousand feet before gradually spiraling down to 7,000ft.
Stacking means pilots move into a holding pattern circling radio beacons.
For this reason, there are several crafts separated vertically by 1,000 feet or more at the identical time in the holding stack. once the plane leaves the holding stack it’s safely directed towards the runway.
Types of linear HOLDING STACKS
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 the 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.
We’ve actually introduced one linear in the UK already; 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 descent approach to the airport.
One airport could have several holding stacks; counting on wherever aircraft arrive from or that runway is in use, or thanks to vertical airspace limitations. for instance, around Heathrow airport, there are four holding stacks known as Bovingdon, Lambourne, Ockham, and biggin.