Perth Traffic Management

The large areas of military and naval airspace in close proximity to Perth International Airport necessitate complicated tracking arrangements for departing and arriving air traffic. In the mid-1990’s the rapidly growing civil traffic and the major military and naval investments at RAAF Pearce and HMAS Stirling led to a review of procedures and airspace management. This review included representatives from Airservices Australia, the RAAF, the RAN, and national and regional airlines and operators.

Restricted areas, which had been based on Pearce TACAN radials, were redrawn to conform with the Perth VOR radials, new SIDs and STARs were developed to, as much as possible, segregate inbound and outbound traffic, and Letters of Agreement detailing responsibilities and coordination protocols were agreed to with the RAAF and RAN. The result is a traffic handling procedure known as the Perth Traffic Management Plan.

The Perth Traffic Management Plan

The Perth Traffic Management Plan applies segregated tracks between outbound and inbound aircraft and minimises the civil transit of military airspace. Traffic handling procedures, including level assignments, are standardised and coordination between adjacent sectors is minimised. These procedures, binding on controllers, are published in South-West Regional Services Local Operating Instructions and, for pilots, in ERSA.

The Perth Traffic Management Plan applies to all aircraft cleared:

· Inbound to Perth, Jandakot or Pearce at FL140 and above;

· Outbound from Perth, Jandakot or Pearce at FL130 and above.

Aircraft below these levels are cleared via flight planned route and are subject to normal coordination between controllers.

Outbound Clearances

Clearances for outbound aircraft are based on:

· The runway in use;

· The intended route of the pilot from 160nm Perth (or the first OCTA waypoint);

· Noise abatement requirements.

Thus the clearance that the pilot receives, such as a Standard Instrument Departure (SID), will take the aircraft via the appropriate outbound system route to intercept the pilot’s flight-planned route by 160nm Perth.

Military aircraft that require to track other than via the appropriate route, such as “special requirements” flights (i.e. minimum fuel) and NAVEX aircraft, are subject to individual coordination.

Outbound Traffic Handling

PHD assigns outbound aircraft A060 and gives “heads up” coordination of the departure to LCI. Once this is done, PHD assigns the aircraft FL130 and hands it off to LCI who may then assign up to FL180. A higher level cannot be given until KNG assigns further climb. KNG is responsible for separating departing traffic with the inbound traffic, which is in Class A and E airspace above FL180, much of which is not yet radar identified. (The base of Class E is A085 in LCI sector but steps up in KNG sector at 90NM Perth to FL180). This does not leave much time for the KNG controller to formulate a procedural separation standard if one is required because most jets and turboprop aircraft quickly reach FL180.

Procedural separation is applied, such as:

• restricting outbound aircraft to levels below the inbound traffic until they’ve passed;

• requiring outbound aircraft to reach a level above inbound traffic by 10 minutes prior to passing;

• establishing aircraft on a laterally separated routes

• vectoring aircraft outside of the tracking tolerances of inbound aircraft until vertically separated, then vectoring them onto their planned route.

In-trail Spacing

PHD provides LCI (and LCI provides KNG) with an orderly traffic flow as follows:

· departing jet and non-jet traffic must be established in independent and separate trails;

· in-trail spacing is be 10nm with no closing IAS.

Before aircraft leave radar coverage (at about 200nm from Perth for the higher-types) and before they are handed off to the procedural sectors, a procedural separation standard must exist.

Track Modification

Once an aircraft is airborne its track may be modified to resolve a traffic confliction or to track shorten the flight. LCI may coordinate a modified route to PHD, such as:

· a heading,

· direct tracking to a SID waypoint at 80nm Perth,

· direct tracking to a 160nm waypoint (after advice from KNG).

A controller will use a heading to vector aircraft out of conflict, such as where inbound and outbound tracks cross, permitting outbound traffic to continue climbing and inbound aircraft to continue descending. Departing aircraft may be vectored 5nm laterally from the SID to allow a faster following aircraft to fly the SID, thus establishing two independent and separate departure trails. Individual aircraft may be track shortened to separate them with other departing aircraft or to clear an inbound traffic sequence.

Inbound Clearances

Inbound aircraft, above FL140, are cleared by an appropriate standard arrival route (STAR), which is determined by:

· the runway in use;

· the original aircraft’s inbound route;

· noise abatement requirements.

Thus the STAR that the pilot receives will take the aircraft off its flight-planned route at the 160nm Perth waypoint, and reroute it by the appropriate inbound system route to Perth. Aircraft planned via non-published routes must be cleared by the nearest suitable system route. Aircraft destined for Jandakot and Pearce fly the STAR waypoints or are vectored around the STAR.

Aircraft cleared at FL135 and below are coordinated directly with Perth TMA for a cleared route (usually direct to Perth). They may opt for a STAR.

Inbound Traffic Handling

KNG assigns inbound aircraft FL190 for descent and hands them off to LCI. As they near the terminal area, LCI assigns them FL140 for aircraft that will cross PHD airspace, and A090 for those entering PHA airspace directly. These are the standard levels for handoff and keep the inbound aircraft in Class E airspace and above the uncontrolled Class G airspace. Any other assigned levels, due to crossing traffic for example, must be coordinated.

No coordination is necessary for aircraft on STARs, who are assigned standard handoff levels.

Separation Standards

Aircraft are said to be in conflict when a separation standard does not, or will not, exist between them. There are, perhaps, more than 100 separation standards, designed by ICAO, involving the three spatial dimensions

· lateral separation,

· longitudinal separation,

· vertical separation,

· and time separation.

These are procedural separation standards. The actual magnitudes of the separation standards do not apply universally in all airspace sectors but are dependent on the nature and quality of the navigational information available to the pilots and controllers; that is, the aircraft's navigational equipment and the navigation aids on the ground.

For aircraft to be separated, a controller needs only one standard to apply. A breakdown of separation occurs when no standard exists between two aircraft. This is not the same as a near miss. Aircraft operating OCTA, in Class G airspace, are not under control; they may have an airprox, but this is not a breakdown of separation because no ATC separation is required.

It is important to realise that a separation standard guarantees just 1 mile of separation between two aircraft when all possible equipment errors and tolerances are taken into account. Thus a 5 mile radar standard, a 20 mile DME standard, a 30 mile RNAV standard and a 10 minute time standard usually mean that aircraft are many miles from each other. But in a worse case scenario they might only be 1 mile apart.

The art of controlling is to be able to move smoothly and seamlessly between standards as aircraft climb, cruise and descend through other traffic so that, in most instances, pilots aren't even aware that differing standards are being applied to separate them from other aircraft in the airspace (nor are they normally aware of which aircraft they are in conflict). This requires the air traffic controller to project each flight ahead and work on future conflicts while maintaining situational awareness of the current traffic disposition.

Vectoring and Speed Control

In enroute radar airspace, the most commonly used separation standards are radar separation of 5nm and vertical separation of 1000ft. The fine weather around Perth often permits visual separation, so that a pilot might be instructed to "sight and follow" another aircraft. When aircraft tracks come into conflict, one or both may be vectored (placed on a heading) until they're out of conflict then instructed to "resume own navigation". Vectoring is also used to permit unrestricted climb or descent of aircraft. The mix of aircraft types means that often a faster jet will overtake a slower turboprop on the climb out of Perth or on descent into Perth, so one must be vectored off track until the faster aircraft has overtaken the slower. For similar types of aircraft on the same route, speed control may be used to maintain radar separation on the climb out of Perth until they reach less congested airspace. Then one can be vectored and the speed control removed. An aircraft with a slow rate of climb may be step-climbed under one with a faster rate of climb.

Aircraft departing Perth tend to spread out. But as aircraft approach Perth they begin converging with other traffic. An orderly sequence of traffic must be organized, not only because common sense tells us that only one aircraft can land at a time, but a mandated separation standard must exist between them, too. This is covered on the next page, Flow Control and Sequencing.