COSCAP
North Asia / Cooperative Development of Operational Safety & /
Continuing Airworthiness Programme

ADVISORY BULLETIN FOR STATES

Subject:INFORMATION TO STATES ON TERRAIN AWARENESS

WARNING SYSTEM (TAWS)

Date:23 December 2003

Initiated by:COSCAP-NA

Bulletin No:001

  1. PURPOSE

a.The purpose of this Advisory Bulletin is to provide States’ with the information on aeroplanes required to be equipped with Ground Proximity Warning Systems (GPWS) and forward looking terrain avoidance function as mandated by the ICAO Standards (and Recommended Practices).

b.The contents of this Bulletin are intended to assist States who are required to develop appropriate legislation, regulations and standards for implementation of the ICAO Standards (and Recommended Practices).

c.This Bulletin is developed to comply with the decisions of the COSCAP-North Asia Steering Committee taken at its 2ndMeeting on 4 – 6 November 2003 on Terrain Awareness Warning System (TAWS) and implement the relevant NARAST recommendations.

2.BACKGROUND

a.The introduction of ground proximity warning system (GPWS) equipment in 1978 resulted in a significant reduction in controlled flight into terrain (CFIT) accidents. However, CFIT accidents do still occur, not only to those aeroplanes that have no GPWS, but also to GPWS-equipped aeroplanes that encounter terrain rising too rapidly ahead of them or that descend below a safe approach path when in a landing configuration. It was with these shortcomings in mind that avionics manufacturers developed a solution to which the International Civil Aviation Organisation (ICAO) responded by publishing Standards and Recommendations concerning retrofit action it believes can or should be taken.

b.GPWS feeds inputs to its computer from a downwards-looking radio altimeter, an air data computer, an instrument landing system (ILS) glideslope signal, and flap and gear selector lever positions: its outputs include visual and aural alerts and warnings when it detects by rate-of-change of position that the aircraft is closing with terrain. To satisfy the ICAO requirement that GPWS should now include a predictive terrain hazard warning function, a terrain awareness and warning system has recently been developed. The predictive function is achieved by feeding the aeroplane's known position (as determined by a flight management system (FMS) or by a global positioning system (GPS)) to a terrain data base, enabling the computer to predict terrain ahead and to the side of the aeroplane's flight path. Terrain features can then be displayed to the flight crew. TAWS therefore overcomes shortcomings associated with GPWS in that it produces earlier alerts and warnings of significant terrain that lie ahead at all stages of flight. Furthermore, with reference to terrain around airfields, it can warn of descent below safe vertical profiles when the aircraft is in a landing configuration and there is no ILS glideslope signal present. Pilots' situational awareness is greatly improved by means of terrain features displayed before them. This displayed information, related to flight path and altitude, means that the alerting and warning capabilities TAWS possesses are less likely to be needed than if GPWS alone were installed. (Note: the acronym EGPWS (Enhanced GPWS) that has been in use for some time describes only one TAWS solution - other solutions are now in the course of development or in production.)

3.SCOPE

a.The scope of this Bulletin is designed to identify the applicable ICAO SARPS on GPWS, which were issued vide Amendment 27 to Annex 6 Part I. The Amendment to the SARPS were 'adopted' by the ICAO Council on 15 March 2002. It was ‘effective’ as of 15 July, 2002 and became 'applicable' on 28 November, 2002.

b.It is also intended to identify the training objectives as may be made applicable to the Operator(s) for implementation of TAWS pilot training.

4.ICAO SARPS

The text below depicts the Standards and Recommended Practices (SARPS) as stipulated in CAO Annex 6 Part 1:

6.15.1 All turbine-engined aeroplanes of a maximum certificated take-off mass in excess of 5 700 kg or authorized to carry more than nine passengers shall be equipped with a ground proximity warning system.

6.15.2 All turbine-engined aeroplanes of a maximum certificated take-off mass in excess of 15 000 kg or authorized to carry more than 30 passengers, for which the individual certificate of airworthiness is first issued on or after I January 2001, shall be equipped with a ground proximity warning system which has a forward looking terrain avoidance function.

6.15.3 From I January 2003, all turbine-engined aeroplanes of a maximum certificated take-off mass in excess of 15 000 kg or authorized to carry more than 30 passengers shall be equipped with a ground proximity warning system which has a forward looking terrain avoidance function.

6.15.4 All turbine-engined aeroplanes of a maximum certificated take-off mass in excess of 5700 kg or authorized to carry more than nine passengers, for which the individual certificate of airworthiness is first issued on or after 1 January 2004, shall be equipped with a ground proximity warning system which has a forward looking terrain avoidance function.

6.15.5 From 1 January 2007, all turbine-engined aeroplanes of a maximum certificated take-off mass in excess of 5 700 kg or authorized to carry more than nine passengers, shall be equipped with a ground proximity warning system which has a forward looking terrain avoidance function.

6.15.6 Recommendation, All turbine-engined aeroplanes of a maximum certificated take-off mass of 5 700 kg or less and authorized to carry more than five but not more than nine passengers should be equipped with a ground proximity warning system which provides the warnings of 6.15.9 a) and c), warning of unsafe terrain clearance and a forward looking terrain avoidance function.

6.15.7 From 1 January 2007 all piston-engined aeroplanes of a maximum certificated take-off mass in excess of 5 700 kg or authorized to carry more than nine passengers shall be equipped with a ground proximity warning system which provides the warnings in 6.15.9 a) and c), warning of unsafe terrain clearance and a forward looking terrain avoidance function.

6.15.8 A ground proximity warning system shall provide automatically a timely and distinctive warning to the flight crew when the aeroplane is in potentially hazardous proximity to the earth's surface.

6.15.9 A ground proximity warning system shall provide, unless otherwise specified herein, warnings of the following circumstances:

a) excessive descent rate;

b) excessive terrain closure rate;

c) excessive attitude loss after take-off or go-around;

d) unsafe terrain clearance while not in landing configuration;

1)gear not locked down;

2)flaps not in a landing position; and

e) excessive descent below the instrument glide path"

5.ACTION BY STATES

a.States may or may not have yet incorporated the revised ICAO requirements for ground proximity warning systems and forward looking terrain avoidance function into their legislation or requirements:

1)States that are yet to do so are requested to initiate action to bring their requirements on TAWS in conformity with ICAO Standards at the earliest.

2)States which find it impracticable to comply with any such international standards or procedure, are requested to give notification to ICAO of the ‘difference’.

b.States may issue the attached Advisory Circular, COSCAP NA - 001 on ‘Guidance for Operators on Training Programmes for the use of Terrain Awareness and Warning System (TAWS) after appropriate modifications as may be considered necessary.

Signed:

Capt. Len J. Cormier

Chief Technical Advisor

COSCAP-NA

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