AMOSSG/4-SN No. 9

25/8/03

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FOURTH MEETING

Montreal, 15 to 18 September 2003

Agenda Item	5:	Aerodrome observation requirements

PROVIDE A MORE ACCURATE DEFINITION OF "AERODROME" AND "VICINITY" FOR REPORTING OF ROUTINE AND SPECIAL OBSERVATIONS

(Presented by Kevin Browne)

SUMMARY
The current definitions of aerodrome and vicinity do not allow pilots, dispatchers, airport operators and forecasters to accurately determine the location of weather phenomena occurring at or in the vicinity of the aerodrome. This paper proposes new definitions for the reporting of routine and special observations in the METAR/SPECI code forms at the aerodrome and in the vicinity of aerodrome.

1.	INTRODUCTION

1.1	In accordance with Annex 3, Chapter 1, an aerodrome is defined as an area on land or water (including any buildings, installations and equipment) intended to be used for arrival, departure and surface movement of aircraft. From an operational perspective, there is no readily available method for the pilot, dispatcher or meteorologist to determine what this is at any particular airport. Further, with the advent and introduction of automated observations, there is both an operational and engineering need to more precisely define the area of an aerodrome. Current practice with human observations provides wide latitude for interpretation by the observer of where the weather phenomena are occurring. Automation is more precise and therefore does not require this latitude.

1.2	Similarly, the issue occurs with reporting weather phenomena in the vicinity of the aerodrome. In accordance with ICAO Annex 3, Chapter 4, paragraph 4.8.6, vicinity is defined as not at the aerodrome, but not further than approximately 8 km from the aerodrome perimeter. Since pilots, dispatchers and meteorologists are unable to determine what constitutes the aerodrome they are also unable to visualize the location of the weather phenomena observed in the vicinity of the aerodrome.

2.	DISCUSSION

2.1	The existing definition of aerodrome lacks specificity for the reporting of weather phenomena for operations. Using a reference point on the aerodrome with a defined area that represents the aerodrome will correct this deficiency. The most appropriate point on the aerodrome to establish this area is the Aerodrome Reference Point (ARP) (ANNEX 14, Chapter 2, Paragraph 2.2). The United States uses the geometric centre of the useable runway surfaces as the ARP. The ARP is located near the initial or planned geometric centre of the aerodrome and is known to both pilots and dispatchers. In addition to having a known fixed reference point, it can be easily identified on an airport diagram.

2.2	Therefore, it is proposed for the reporting of routine and special observations, the aerodrome would be referred to as "the area within 8 km of the ARP". This definition would provide uniformity and eliminate the irregular and mostly unknown shapes of almost all aerodrome perimeters, especially those located in urban settings.

2.3	In the vicinity should be defined as a specific area with reference to the ARP. To be specific it should be defined as "that area adjacent to the aerodrome that extends from 8 km to not more than 16 km of the aerodrome". This would allow pilots, dispatchers and meteorologists to more accurately assess the meteorological conditions that may affect decisions they are required to make.

2.4	The United States is currently using the above reference for the automated reporting of thunderstorms (TS). Existing technology allows for greater accuracy in the reporting of TS when compared to human observations. With the automated reporting of TS, pilots, dispatchers, meteorologists and airport managers now know more precisely whether a thunderstorm is occurring at the aerodrome (TS) or in the vicinity (VCTS). This is very significant, since a thunderstorm erroneously reported at the aerodrome while it is actually in the vicinity can result in unnecessary delays. Usually, observers will err on the conservative side and report a thunderstorm at the aerodrome if they are not completely confident that it is located in the vicinity.

3.	CONCLUSION

3.1	There is a need to change the definition of an aerodrome and in the vicinity of an aerodrome as it applies to the automated observing and reporting of thunderstorms. The United States has a methodology in use to resolve this issue.

4.

4.1	The United States proposes that the meeting review the definition for an aerodrome and in the vicinity of an aerodrome with regard to automation.

5.	ACTION BY THE MEETING

5.1	The meeting is invited to act on the recommendation provided in this paper.

— END —