Approach sequence methodology[PDF]

Introduction

As explained in the 'Approach traffic management' document, the main goal of approach management is to organize a sequence of aircraft providing a continuous flow towards the final approach path.

The approach management can be done using:

  • Procedural control: APP controller will use only the IFR procedure and holding combined with a direct route to the intermediate fix, altitude change and speed instruction in order to maintain and create separation
  • Radar vectoring: APP controller will use the radar to guide the aircraft outside the published tracks in order to optimize the distance between aircraft in order to increase the arrival of the maximum number of aircraft with the least average delay
Radar vectoring is today one of the main methods to achieve efficient sequencing. Point merge operation, where it is published, is now the new optimisation procedure in development in Europe.
Whenever a controller starts radar vectoring, he has to take responsibility of all flight navigation parameters: heading, altitude and speed (descent rate if applicable) until interception of the IFR final approach track


If you want to learn the basics of final interception track, please consult the Final approach track interception Document. This document will cover only the initial and intermediate approach sequence methodology.

Minimum regulation distance

ATC shall apply a margin for regulation distance between aircraft in order to handle unexpected changes in flying conditions and sequence situations like:
  • Pilot error (track change, level change, speed change)
  • Wind condition change ( aircraft ground speed change)
  • Radar delay (or IVAO network latency)
  • Human factors related to ATC (workload and stress, emergency handling by ATC, fatigue)
  • Human factors related to ATC (emergency/pan stress, fatigue, distraction)
  • IVAO related issues (simulator crash, pause mode …)
  • Aircraft going into emergency/pan condition (possible change of track, level and/or speed)
ATC should never regulate its traffic just at the minimum separation distance. (no margin)
Approach traffic APC 3.jpg
There are no specific rules and no predefined procedures to define the regulation margin distance. It should be a typical value of 2NM minimum which corresponds with about 30 sec flight time at 220kt.


Regulation target

A typical 5NM separation on the final approach path is one of the most used methods to manage the traffic flow. This target of 5NM on final approach will create the need of a 2 minutes spacing sequence of aircraft.
Approach traffic APC 4.jpg

Today, timed based separation is the method applied in modern air traffic control systems.

The table below will give you the separation time to monitor by using speed vector on IVAO ATC softwaree calculated in function of the final separation distance wanted:

Final separation wanted (on final approach path) Mean approach speed (during final approach path) Separation time (speed vector)
8NM 150KT 3,2 min
7NM 150KT 2,8 min
6NM 150KT 2,4 min
5NM 150KT 2 min
4NM 150KT 1,6 min
3NM 150KT 1,2 min
2.5NM 150KT 1 min


If you handle light aircraft, the separation time should be increased during final approach as light aircraft use lower mean approach speed during final approach.

Final separation wanted (on final approach path) Mean approach speed (during final approach path) Separation time (speed vector)
8NM 120KT 4 min
6NM 120KT 3 min
5NM 120KT 2,5 min
3NM 120KT 1.5 min


Baseline regulation

The basic of regulation is to use the final approach path as a baseline.

This basic method is used combined with radar vectoring.

Each aircraft should be vectored by taking into account the preceding aircraft and the need of separation between all traffic.

Approach traffic APC 5.jpg


Regulation via one point

The APP controller should create the sequence via one point which is not on the final approach path.
A minimum vertical separation of 1000 ft between 2 successive aircraft should be used during the regulation separation establishment before obtaining the effective and stable regulation separation.

With this method, we secure the regulation in the final approach path before the interception. All aircraft are performing the same final path interception which improves the pilot awareness of the situation.

On IVAO ATC softwaree, you can use the range rings with radar centred on the regulation point.

Below, 2 examples are presented:

Approach traffic APC 6.jpg


Regulation via two points from the same side

The APP controller can use vectoring or regulation via two points from one side.
A minimum vertical separation of 1000 ft between 2 successive aircraft should be used during the regulation separation establishment before obtaining the effective and stable regulation separation.

The disadvantage of regulation via two points from the same side is that the APP controller may have problems with maintaining all aircraft on specified routes and create lateral separation issues when the 2 paths are near parallel.

The difficulty is to maintain double separation between some aircraft. The pressure of traffic flow against ATC regulation trends to reduce the double separation between aircraft.

Approach traffic APC 7.jpg


Regulation via two points from two sides

Radar vectoring via two points from two sides is used in enlarged traffic from more directions, especially at airports with parallel runways.

The two regulation points shall share the same distance to the final axis approach in order to ease the regulation separation on the final axis and reduce the possibility of instructing a holding procedure.

Approach traffic APC 8.jpg


Regulation using a mixed solution

In complex situations where arrivals are coming from several areas of controller airspace, the APP controller may use a combination of the solutions given above. He can change the strategy in function of the traffic flow.

Regulation using flight path procedure

The flight path procedure is a procedural arrival procedure to sequence traffic in long waiting lanes.
Approach traffic APC 9.jpg

ATC will shorten the flight track of aircraft if needed by the optimal regulation target.

Approach traffic APC 10.jpg

On the sequence above the red arrow shows how to optimize the traffic regulation flow by inserting an aircraft between two others with a sufficient available space (between aircraft at SOGAP and aircraft at DB421).

Regulation using point merge

The point merge procedure is a new regulation procedure initiated by Eurocontrol (SESAR program). It should provide benefits in terms of safety, environment and capacity, even with high traffic loads.

The new sequencing techniques aim primarily at improving the final part, in particular securing the ILS interception and reducing noise nuisances even under high traffic conditions, as well as optimising descents, reducing workload and communications.

Point Merge is designed to work in high traffic loads without radar vectoring. At some airfields point merge operation has been combined with radar vectoring.

Point Merge is based on a specific RNAV route structure (precision 1NM), consisting of a point (the merge point) and pre-defined legs (the sequencing legs) equidistant from this point.

Approach traffic APC 11.jpg
The sequencing is achieved with a “direct-to” instruction to the merge point at the appropriate time.

The legs are only used to delay aircraft when necessary (“path stretching”); the length of the legs reflects the required delay absorption capacity.

Aircraft using point merge operation shall have the RNAV capacity precision 1NM. The APP controller shall not use procedural point merge operation on non-RNAV aircraft.
Point merge principles can be used as a method for vectoring radar as well

According to Eurocontrol, Point Merge promises a significant increase of trajectory predictability and reduced track dispersion, which would enable more efficient sequencing of the approaching aircraft.

Depending on the operational and environmental constraints, and on the design choice made, these are the expected benefits:

  • simplification of controller tasks
  • reduction of communications and workload
  • better pilot situational awareness (if procedural control)
  • a better view of arrival sequences
  • improved containment of flow
  • better trajectory prediction
  • better airspace management
  • standardisation of operations


Regulation using point merge from two arrival sides

At some larger airfields, you can find a point merge with 2 IAF from two arrival sides.
Approach traffic APC 12.jpg
The altitude between the 2 arrival sequencing legs shall be different and vertically separated.

The same final altitude shall be reached when reaching the point merge after regulation horizontal separation is applied and maintained.

Approach traffic APC 13.jpg



See also

Reference

  • None

Author

  • VID 150259 - Creation
  • VID 150259 - Article Split from Approach management document - September 2019

DATE OF SUBMISSION

  • 12:45, 7 January 2020

COPYRIGHT

  • This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.

DISCLAIMER

  • The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.