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The following is the text of a presentation made to an ICAO ATM Seminar held in Mexico in November 1997. The document was authored and presented by George Livingstone, the then Asst. Director of Civil Aviation on behalf of the Civil Aviation Division, and the Government of  Trinidad and Tobago.

While the plans and procedures mentioned have never been officially accepted as part of the Division’s macro Aviation policy with respect to Airspace Planning within the Eastern Caribbean, it however, represented the views of the author at that time.

The author wishes to acknowledge the assistance of Mr. Trevor Dowrich the Chief Air Traffic Controller who assisted in the editing of the document and his help at the meeting with the presentation of the visual aids associated with the subject.

   AIRSPACE PLANNING WITHIN THE PIARCO CTA/FIR

INCLUDING  THE  PRESENT  IMPACT  OF  THE  USE  OF 

RNAV AND RANDOM  ROUTES

ON AIRLINES AND SERVICE PROVIDERS.

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  Contents

  Introduction

The Present

  • The Procedural Environment

  •  Determination of Separation in the Procedural Mode

  • The Eastern Caribbean (ECAR) Air Route Structure

  • The Challenges and Implications of RNAV routes in the Procedural System

  • Procedural Options for Level Changes

  • RNAV Separation Criteria

  • Challenges of the Oceanic Airspace

The Future

  • Possible Solutions for Mid and Long Term

  • SIDs, STARs and New Tracks in the Oceanic Airspace

  •  Radar Linking

  •  Restructuring of Routes in the Oceanic

  •  General Improvements

Comments and Conclusions

  INTRODUCTION

I wish to thank the organisers of this seminar for giving me the opportunity to address you on a topic which is now gaining greater and greater importance as we seek to establish in our areas of jurisdiction the facets and principles for the various components of the new CNS/ATM systems for the future of aviation, a discipline now referred to as Air Traffic Management.

Air Traffic Management, in itself, incorporates many aspects of the aviation environment.  Any general discussion of ATM, will of necessity include at least concepts and topics such as Airspace Management, Reduced Vertical, Lateral, and Longitudinal Separation, Air Traffic Flow Management, Conflict Prediction and Conflict Alert, Standard Instrument Departure Procedures, Standard Arrival Routes etc.  Such is the diverse nature of the topic itself.

The varied nature of the topic has meant that if  I am not to be here for an hour or more, I would have to select one of the categories on which to make this presentation.  As such I have chosen to deal with Airspace Planning within the area over which Piarco has jurisdiction, including the implications of RNAV and random Routes, and the present impact on the airlines which use the system, and the providers who operate the system.  The airspace with which I am familiar is the Piarco Upper and Lower Control Area and its Upper and Lower Flight Information Region, hereinafter, for ease of discussion, referred to primarily as the CTA/FIR.

 In dealing with the subject matter I have opted to use a practical- approach, since, in my opinion, all matters related to the Air Traffic Services result in the provision of an operational service to the airlines.

  In analyzing this situation it will be important: -

  1.    Firstly to look briefly at the present scenario of the procedural environment, and the route management challenges related to the existing traffic situation as it applies to the present route structure. 

(In this context, I will need to explain briefly how the Procedural environment works and consider some of its inherent limitations)

  2.    Secondly to look at the possibilities for the future of the sub region's airspace with a brief discussion of workable solutions which are consistent with the ICAO route and area navigation concepts.

(In this context, we look at the user’s need for RNAV Routes, and the providers’ capacities to arrange an environment in which there will be continuing safety with a manageable workload for air traffic controllers.)

 

THE PRESENT

The increase in traffic through the Piarco FIR has brought with it a number of challenges in the local management and controller management of the resulting air traffic scenarios.

Large numbers of transatlantic aircraft via established and RNAV routings are either transiting the Piarco CTA/FIR or operating into or out of International Airports in the Eastern Caribbean.  Challenges in the science of keeping aircraft safely separated now exist due to a number of inter-related factors.

  The Procedural Environment

To understand why this environment presents a gnawing challenge to ATC, I will need to provide a brief overview at this point of the Procedural ATC Environment and how it works for the benefit of those who may not be familiar with this type of operation.

I suppose a simple way to define a procedural environment is to say that it is a non Radar environment, and then argue that every one here knows what is a radar environment.  But a more precise definition would be that a procedural air traffic control environment is one in which aircraft are separated by utilizing pilot reports and estimates for predetermined points.  These reporting points are usually overhead navigation beacons of various types, or other significant positions based on bearings and distance from these beacons.  Pilot reports are then compared with those calculated by the controller and verified where there are discrepancies, and then used to project the expected future positions of the aircraft. This information is then used to space aircraft longitudinally, or depending on whether, initially, there is adequate longitudinal spacing, to effect level changes.

Determination of Separation in the Procedural Mode.

In this type of environment and within Piarco’s control airspace, the controller's tools for effecting separation, are basically the NDB, VOR and DME stations.  These navigational aids, when so spaced are also used to determine lateral separation when there is no overlap of the airspace to be protected.  The navaids are not necessarily strategically placed, as may be the situation within the USA, but geographically and conveniently placed owing to the fact that the area is not a large land mass but several small islands.

A controller sits at a display board with designators of the Reporting Points arranged in such a manner as to represent the chart of the route structure and the area to a trained eye.  Flight Progress strips for the aircraft which form the current traffic scenario, are placed appropriately in time or level sequence under these designators.

The Controller takes and keeps a mental picture of the traffic situation, in three dimensions, and projects the flight path of the aircraft, based upon the estimates provided, as previously mentioned, in order to determine whether separation will exist in the future.  He/she then takes action accordingly to ensure such future separation along the route.

The ECAR Route Structure

The design of a route structure in a busy environment should normally facilitate the provision of separation, particularly within the arrival and departure phases of flight.  At present the ECAR Route structure has slowly evolved to be comprised basically, of direct connections between city/island pairs and at present does not necessarily always provide for automatic separation between aircraft operating along these routes.  The controller therefore has to be constantly vigilant as to when such separation between aircraft on the same, converging and crossing routes, will cease to exist.  This again is all based upon estimates.

Among the ICAO standard methods for dealing with separation between routes based upon the conventional navigation aids are:-

1.    The establishment of routes from a VOR station so that their angular divergence in the arrival and departure phase, meet the ICAO criteria set up for separation.  If this were strictly adhered to, there would be no routes emanating from a VOR station that are closer than 15 degrees apart.  However this is not always practicable. 

2.    The Diamond Concept.  This concept also makes use of VOR signals and is used for relatively short distances, where the route, in one direction, forms a half of a Diamond shape, and in the opposite direction-- the other half.  

3.    The RNP Concept.  Within recent times, as many of you know, ICAO has established a new concept which specifies the minimum navigation performance accuracy necessary for operation within a defined airspace.

However, neither of the first two concepts, was ever applied within the airspace over which Piarco has jurisdiction.  We have now begun to actively consider the implications of the RNP concept, and how it may be applied within the area for which we are responsible.

Today, I would like to point out some of the existing challenges, both for users and for us, with the hope that there will be a greater understanding of the present system and its constraints.  This may be particularly informative for airline personnel who are more familiar with a Radar environment than with the Procedural environment and its challenges.

  The Challenges and implications of RNAV routes in the procedural system. (Controlled Airspace)

Allow me now the privilege of talking briefly about random routes and the present implications for users and for us within the CTA/UTA.  In my discourse, I will make generic reference to random or RNAV routes, for ease of discussion.

GNSS navigation, whether on specific RNP or random routes, allows operators to select the most efficient flight paths for their aircraft between departure and destination points, allowing for consequential savings in fuel and time.  Providing for these preferred routes, is acknowledged to be extremely beneficial to the airline industry, in order for users to benefit from improved navigation technology, and despite present constraints, continues to be a major objective of the ATS providers.

We have found that in the past and even, to some extent, at present in the effort to provide airlines with their requested routes, controllers, have been granting RNAV direct routes and thereafter looking for methods to provide the necessary separations between aircraft for level changes.  Approvals to preferred levels and ad-hoc level changes have not always been expeditious.  Why not?

Separation of aircraft in the procedural environment, is most easily achieved when aircraft involved are proceeding directly to or away from the navigation aid on which the separation is predicated.  However in many cases of aircraft on random RNAV or direct routes, the navaids used to provide separation in the climb or descent profile are offset from the direct route, and very often the separation is difficult to achieve and requires excessive pilot/controller interchanges.

Procedural options for level changes. (RNAV routes)

The relatively new RNAV longitudinal separation criteria in Document 4444 provides for a basic 80 NMs separation between RNAV equipped aircraft in various circumstances.  While this has proven useful in instances involving high level movements, in many other scenarios this separation may be considered a bit exorbitant for application at the medium levels and lower airspeeds.  In these circumstances the options to expedite the level changes may then involve, in an RNAV situation, the re-clearing of one or both aircraft to proceed initially towards the navaid from which direct navigation reference will then be possible, with level restrictions to ensure separation.  Ensuring that the level change is completed outside of the required 15 miles, the separation is thus accomplished.

RNAV Separation Criteria?

The majority of developing countries, has not been able to develop detailed RNAV separation criteria and are still dependent upon the ICAO textbook type standard, many of which are not particularly compatible with the justifiable expectations of most cost-conscious airlines which, of necessity are now equipping their fleet with advanced airborne navigation equipment.

Within the Piarco CTA, new initiatives to be implemented, relative to the application of the ICAO Concept of Protected Airspace, may allow for more efficient management of the airspace.

Increasing Traffic numbers and the need for more direct routings

The CNS/ATM concept has long been accepted by many countries.  Improvements are planned where global changes in route designs are expected to cater for more direct paths.  These structural route design changes are now being established in many areas of the world as users press for and providers seek to afford the facilities which will bring early benefits to users who are equipped with the new avionics technology.  This is not extremely difficult within the radar environment, as monitoring and radar separation can apply as may be necessary.

With the increasing numbers of GNSS equipped aircraft within the ECAR, ATS providers are already seeing an increasing number of requests for more direct Trans-Atlantic and TransCaribbean routes.  The traffic challenges are compounded, as we couple the factor of increased traffic levels with the need to allow for more direct routes.  

Part 11