International Civil Aviation Organization

World-wide CNS/ATM Systems

Implementation Conference

Rio de Janeiro, 11 – 15 May 1998

WW/IMP–WP/3

26/3/98

Item 1

Agenda Item 1:	Overview of CNS/ATM systems implementation

CNS/ATM SYSTEMS AND THE REDUCTION OF CONTROLLED FLIGHT

INTO TERRAIN (CFIT) ACCIDENTS

(Presented by the Secretariat)

Information Paper

SUMMARY

This paper summarizes the contribution that the introduction of CNS/ATM

systems could make to the prevention of controlled flight into terrain.

1.	Introduction

1.1	It is beyond dispute that most accidents take place in the departure, the descent, the approach and the landing phases of flight, and that the most serious problem with regard to these accidents is the occurrence of controlled flight into terrain (CFIT).

1.2	Whilst terminal airspace is usually provided with better surveillance and communications than en-route airspace, this is by no means the universal case with regard to surveillance. The efficient, and universal, monitoring in the initial approach, the terminal area, the intermediate and the final approach phases of flight would provide the possibility for the greatest improvement in the safety of flight.

2.	Systems which contribute to the prevention of cfit

2.1	Currently the means to do this are provided by disparate systems both in the air and on the ground. Many aircraft are provided with terrain hazard warning systems which themselves have widely varying capabilities. These capabilities are being improved, with the later models of the conventional system based on the use of radio altimeters, and with the introduction of predictive terrain hazard warning systems based on area navigation (RNAV) systems and a terrain data base. These systems are not universally provided despite the adoption by the 31st Session of the ICAO Assembly of Resolution A31/9, in October 1995, which urged States to implement the carriage of terrain hazard warning systems in international and in domestic operations. The success of terrain hazard warning systems, when provided, is critically dependent upon operator policy and the education and training of all personnel in the CFIT problem and the response required to a hazard warning.

2.2	Many aircraft are provided with pressure-altitude warning transponders, SSR Mode-C and increasingly Mode-S, and other similar equipment. However, there is a problem of international incompatibility of radar systems and transponder equipment. Both primary and secondary radar are used to monitor navigation performance in azimuth. Altitude information, whilst available from aircraft, has been traditionally ignored as a routine means of providing additional safety in the terminal area phases of flight, except where a minimum safe altitude warning (MSAW) system has been provided in association with the Air Traffic Control (ATC) terminal and approach radar service. Other proprietary systems, where some aircraft have had, for a number of years, the capability of automatic reporting of flight parameters, have not been exploited for lack of will and an appropriate infrastructure.

2.3	The MSAW service is acknowledged to be successful as a system for the prevention of CFIT. However, the system has been implemented in very few States despite the fact that the majority of the ATC radar systems in use have the basic capability to provide the service. These radar systems have not been provided with the appropriate system software or a terrain database which are requirements for the provision of an MSAW service. The other requirement, as noted above is a pressure-altitude reporting transponder in the aircraft.

2.4	The requirement for many transport aircraft to be equipped with airborne collision avoidance systems (ACAS II) from 1 January 2003 and many more smaller aircraft to be equipped from 1 January 2005, in international operations will mean that a large number of aircraft will be equipped with SSR Mode-S transponders. A requirement, applicable from 5 November 1998, requires all aircraft engaged in international operations to be equipped with a pressure-altitude reporting transponder. Regional agreements and the designation of airspace by States will extend the carriage of pressure-altitude reporting transponders in domestic operations. These transponders will be available to contribute towards the prevention of both airborne collision and CFIT.

3.	The contribution to approach phase safety from cns/atm systems

3.1	The opportunity provided by the introduction of CNS/ATM systems must be taken to integrate the available information within a comprehensive safety system and to provide to aircraft, at least equipped with a pressure-altitude reporting transponder, a minimum safe altitude warning system. Aircraft equipped with CNS/ATM systems will be capable of self-monitoring and automatic reporting, to both the flight crew and ATC, of significant flight deviations. These systems should be able to detect and report deviations from clearances and from instrument procedures in real time and with sufficient time available for the correction of the flight path or the initiation of a missed approach.

4.	The efficient and safe use of airspace

4.1	The intent of the introduction of CNS/ATM systems is to permit more flexible and efficient use of airspace, and to enhance traffic safety and regularity of flight. One of the most beneficial ways in which this could be exploited to increase the safety of flight would be to take a part of the dividend of the increased efficiency in the use of airspace and to raise the minimum altitudes available for flight, particularly in terminal areas where terrain constitutes a problem. We have in the past been overconfident about the minimum allowed terrain clearance. There is also insufficient universal knowledge of, and application of, altimeter corrections in conditions of low temperatures, low pressure and strong winds. If there is no demonstrated need to operate close to terrain before entering an aerodrome circuit area or before initiating an instrument approach, then these lowest altitudes currently available should not be used.

5.	Summary

5.1	Capabilities of the CNS/ATM systems being introduced include the monitoring of navigation, adherence to clearances, adherence to instrument procedures for departure, arrival and approach to landing, and the provision of alerts to both flight crew and ATC of significant deviations. These systems must be able to exploit the integration of all available information. Every effort should be made to provide for increased terrain clearance prior to the commencement of a visual or an instrument approach.

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