AMOSSG/4-SN No. 13

21/8/03

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FOURTH MEETING

Montreal, 15 to 18 September 2003

Agenda Item	5:	Aerodrome observation requirements
5.1:	Reporting requirements and criteria

DEFINITION OF "AERODROME" AND "VICINITY"

(Presented by Dennis Hart)

SUMMARY
This study note describes a proposed more accurate definition of "aerodrome" and "vicinity" to overcome the difficulties when applying current definitions in daily practice.

1.	INTRODUCTION

1.1	The current definition of an aerodrome and its vicinity in accordance with Annex 3 results in an imprecise determination of the location of weather phenomena at or in the vicinity of the aerodrome when reported in routine en special observations. At this moment this is a disadvantage for users, observers and forecasters. The lack of strict definitions becomes even more evident when fully automated observations are put into place.

1.2	After an indebt discussion on this subject during the Meteorological Divisional Meeting 2002 it was decided that the AMOSSG should be tasked to study further on this matter and to propose definitions for the terms "vicinity" and "aerodrome" in relation with the reporting practices on aeronautical observations.

2.	DISCUSSION

2.1	In accordance with Annex 3 an aerodrome is defined as an area on land or water intended to be used for arrival, departure and surface movement of aircraft. Similarly the vicinity of an aerodrome is defined as not on the aerodrome but not further then approximately 8 km from the aerodrome perimeter. It is not operationally feasible for users, observers, forecasters and automated systems to determine these areas at any particular airport.

2.2	More precise definitions of an "aerodrome" and "vicinity" should incorporate conditions to be general acceptable as more accurate and of operational use:

—	Feasible for both small and extended aerodromes;

—	Clear and unambiguous defined areas that represent the aerodrome and its vicinity;

—	These defined areas shall have an incorporated relation with the aerodrome extends, E.g. at a small airport the definition of "aerodrome" will also result in a small area vice versa, and

—	These defined areas shall have a relation with a known reference point at an aerodrome.

2.3	To meet these conditions it is proposed to change the definition of "aerodrome" and "vicinity" in definitions using known references as the "Aerodrome Reference Point (ARP)" and the "end of the runway". The ARP is located near the initial or planned geometric centre of the aerodrome. The end of the runway is the start or end of the hardened surface intended to be used for landing and starting aircraft.

2.4	Using these known aerodrome specifics a new quantity is introduced, the Aerodrome Radius. The Aerodrome Radius is defined as the lateral distance from the end of the runway at greatest lateral distance from the ARP (rounded up to the nearest 100 meter). The forthcoming proposed definition for aerodrome is then "the area within the Aerodrome Radius of the ARP".

2.5	The vicinity of an aerodrome in this proposal is defined as the area adjacent to the aerodrome that extends from the Aerodrome Radius to the Aerodrome Radius plus 8 kilometres.

2.6	In Appendix A a graphical interpretation of the proposed definitions is displayed. Appendix B gives a practical indication of "aerodrome" and "vicinity" for several example airports.

3.	CONCLUSION

3.1	To overcome the self-interpretation by observer, forecaster and user in cases of locating weather phenomena on the aerodrome and in its vicinity a revised definition for aerodrome and vicinity is suggested. In cases where fully automated observations are in place the need for exact definitions is even more evident. The above-mentioned proposed definitions, 2.4 and 2.5, are meeting all conditions to have exact and unambiguous definitions for vicinity and aerodrome.

4.	ACTION BY THE GROUP

4.1	The group is invited to:

a)	note the content of this paper;

b)	agree on the proposal stated in paragraph 2.4;

c)	agree on the proposal stated in paragraph 2.5, and

d)	undertake any further action, if necessary.

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