Investigate Applications of Provision of Area Proximity Warnings

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Investigate Applications of Provision of Area Proximity Warnings

44TH ANNUAL CONFERENCE, Melbourne, Australia, 17-22 April 2005

WP No. 91

Investigate Applications of Provision of Area Proximity Warnings

Presented by TOC


1.1.  Working paper number 92 of the 2004 conference produced a definition of Area Proximity Warning (APW) and Area Proximity Warning System (APWS). The fact that these systems could be deployed as either a safety net or a Controller Tool (CT) was highlighted in the working paper.

1.2.  Because an area proximity warning system could be utilised in a number of capacities, generally dependent upon the nature of the airspace being protected, guidance material was sought to assist Member Associations (MAs) in evaluating warning systems.

1.3.  The purpose of this paper is to provide information regarding the implementation of area proximity warning systems.


2.1.  In the modern world of aviation there are a variety of different types of airspace that could possibly require protection. There are danger areas, restricted areas, special use areas, prohibited areas, temporary reserved areas, military areas and other locally defined special airspace areas to name a few. The airspace will have been established for a specific purpose and there will be a requirement to either keep aircraft operations clear of such areas or at least advise a pilot of the imminent penetration of some types of airspace.

2.2.  In determining how an area proximity warning system will be implemented, a fundamental decision will need to be made with respect to the type of airspace that must be protected. Some types of airspace can be considered “safety critical”, examples of which are live firing areas or areas established for military air combat manoeuvring. Other types of airspace are “non-safety critical”; examples of which are noise sensitive areas or conservation areas. The fundamental difference is whether entry into the area constitutes (or may constitute) a hazard to the safe transit of an aircraft.

2.3.  Making this decision does not preclude operating a system with varying types of airspace being protected. It has been previously established that a single functionality can be utilised as both a CT and a safety net, depending upon the parameters and design of the system. An APWS can similarly be deployed as a safety net function, a CT, or both. What is vitally important is that the presentation to a controller of any warning is appropriate to the airspace and varies according to the safety critical nature of the airspace.

2.4.  If an area proximity warning system is to meet the requirements of both a CT and a safety net then it is vital that the system is able to recognise different types of airspace and present different warnings to a controller depending upon this differentiation. It would not be appropriate, for example, for a system to generate the same warning for an aircraft about to enter a live firing area as one about to descend into a noise sensitive area. In the first case, an immediate response is required whereas in the latter case, the alert could be considered as an advisory.

2.5.  Provided an APWS is able to meet the requirement as stipulated in 2.4, then it can be deployed for the purposes of a safety net and also as a CT. If this requirement cannot be fulfilled then the system must only provide warnings for one type of airspace, either as a CT or a safety net function. Additional requirements for APWS are similar to the requirements for other safety net functions or CTs. These include:

a)  Alerts must be unique, distinguishable, timely and actionable;

b)  Nuisance alerts must be kept to a minimum;

c)  Controllers must be provided with clear, unambiguous instructions relating to actions required in the event of an alert;

d)  Controllers should be provided with the ability to suppress alerts on individual aircraft when necessary.


3.1.  Area proximity warning systems can be used to provide a level of protection for a variety of airspace types.

3.2.  Area proximity warning systems can be deployed to operate as a CT, a safety net or have dual functionality depending upon system design.

3.3.  If an APWS has dual functionality, then the nature of the alerts generated must be clearly unique and actionable by a controller. Other requirements for any CT or safety net function must also be met.


It is recommended that;

4.1. This paper is accepted as information material.

Last Update: September 29, 2020  

March 27, 2020   233   Jean-Francois Lepage    2005    

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