- 1 Introduction
- 2 Holding pattern and stacking process
- 3 Management
- 4 En-route holding to prevent overload and stack creation
- 5 See also
- 6 Reference
- 7 Author
When an air traffic controller has such an amount of traffic in his approach area that he cannot handle more traffic for a determined or non-determined period of time, the air traffic controller can use the holding pattern to put the traffic on hold before taking them into account inside his approach sequence.
Holding pattern and stacking process
- Constituted of 2 half turns joined by a straight flight leg. The straight flight length is generally 1 minute flight duration or a distance based on a DME.
- Constituted of a reference fix where the holding pattern starts and where an aircraft can exit to continue the next procedural approach phase of the flight. The turn in the holding pattern is a right turn (like the figure below) by default but it can be published to the left.
- Flown at a certain altitude with a maximum speed restriction where an aircraft can exit to continue the next procedural approach phase of the flight.
We shall discuss the following situation:
- ATC creates a holding stack
- ATC fills the stack with aircraft
- ATC removes aircraft from the stack
- ATC needs to create a multi stack
- ATC manages stack in function of separation altitude
Creating a holding stack
On charts, holding patterns are usually published at the initial approach fixes (IAF) which is the end of the arrival phase of flight, and before starting the approach phase. This point associated with the published holding pattern should be taken as holding stack reference point where the air traffic controller starts to construct his waiting stack.
Filling the stack with aircraft
Remember the goal of the air traffic controller in an approach area: he takes the aircraft arriving at high level and controls them to delivery on the final approach path at lower altitude. Arriving aircraft should have a higher altitude than aircraft in the approach sequence.
In our example, the first aircraft is on the first floor of the holding stack. The second aircraft shall be inserted on the second floor above the first one. The third aircraft shall then be inserted on the third floor above the second one.
Removing aircraft from the stack
The controller will remove aircraft from the first floor of the holding stack, or the aircraft with the lowest altitude in the stack and normally when the aircraft is on the inbound leg of the holding pattern.
In our example, the aircraft at the first floor will exit the stack at first. The air controller should then insert this aircraft into the approach regulation sequence.
ATC can remove aircraft from the first floor anywhere from the pattern if the approach regulation sequence requires so.
The reasons to choose the first floor of the holding stack or the lowest altitude is:
- altitude is more compatible with the next approach phase of flight than higher altitude
- no conflict is possible with other aircraft in the stack if the lowest altitude is selected
In our example, the aircraft at the second floor will first descend to the next lower level (first floor).
In our example, the aircraft at the third floor will descend to the next lower level (second floor) as the lower aircraft has reached the first floor and the second floor is free
Multi stack creation
If an air traffic controller uses a published holding pattern to create his stack, he should be limited by the protection area of this holding pattern. The protection area is an altitude where the holding patterns are not protected against other IFR routes and procedures. The air traffic controller can use levels above this protected area but the situation needs extra safety management in order to ensure protection of these levels.
In conclusion, the number of traffic to insert inside the stack is limited by the maximum altitude of his area of responsibility.
In addition, the approach controller can handle arrivals which come from different directions and IAF.
In all these situations, the approach controller can create a multi stack in his area of responsibility or create linked stacks with the en-route traffic controller .
In the figure below, there is an example of several holding stacks creation over different fixes in the approach area. The air traffic controller can handle each holding stack separately.
As the approach area is limited in terms of altitude, the stack is also limited for its maximum altitude. If we have too many aircraft to stack, the higher controller (en-route controller) can initiate another stack before the approach area.
These stack altitudes should be higher than the previous stack.
Separation should be done by the air traffic controller between all stacks.
Managing a stack in function of separation altitude
- To prevent aircraft to create conflict alerts when aircraft crew select a wrong altitude or making an undershoot of altitude during descent.
- To also have free spare levels in order to integrate the going around aircraft inside the holding stack.
En-route holding to prevent overload and stack creation
In real life, each aircraft is regulated from the clearance given on the ground until its arrival on the approach area. Complex systems calculate arrival estimations of each flight in order to anticipate the overflow of controlled areas. In IVAO, we do not have such complex systems, but ATC to ATC communication should be used to share the overflow situation at some destinations. When desired, the en-route controller can create pre-regulation sequences by reducing the speed of aircraft or by using an en-route holding pattern (see below) in order to create delay.
- VID 150259 - Creation
- VID 256272 - Wiki integration
DATE OF SUBMISSION
- 03:34, 14 May 2021
- This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.
- The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.