Let’s begin from the start! The definition of holding (or flying a hold) in aviation field means that some manoeuvres of airplane before the landing. Incoming airplane should generally be stacked when an aircraft that has arrived at their destination however cannot land , thanks to the traffic jam, poor weather, or runway inaccessibility.
Stacking means pilots move into a holding pattern circling radio beacons.
Holding stacks work as waiting area for an airplane before landing. Then the airplane is within the “waiting room” the traffic controller with efficiency organises the landing directions and runway. For this reason, there are several craft separated vertically by 1,000 feet or more at the identical time in holding stack. once the plane leaves the holding stack it’s safely directed towards the runway.
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.