AMOSSG/5-SN No. 3

22/3/05

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FIFTH MEETING

Montreal, 11 to 14 April 2005

Agenda Item	6:	Aerodrome forecast requirements

OVERVIEW OF PROGRESS WITH RESPECT TO AERODROME FORECAST REQUIREMENTS

(Presented by the Secretary)

SUMMARY
A summary of progress made by the group with respect to aerodrome forecast requirements is given together with an overview of outstanding tasks for consideration by the group.

1.	INTRODUCTION

1.1	This study note summarizes the tasks that are under review by the group that concern aerodrome forecast requirements, together with an indication of previous discussions and, in some cases, suggested courses of future action. Additional tasks that have arisen since the AMOSSG/4 Meeting are also introduced.

1.2	The attention of the group is drawn to the consideration of whether changes are necessary to the provisions, principally of Chapter 6 and Appendix 5 of Annex 3 — Meteorological Service for International Air Navigation.

2.	DISCUSSION

2.1	Alignment of TAF amendment criteria with the criteria used for the issuance of SPECI (ANC task 9206 a) 7)

2.1.1	The group will recall that the MET Divisional Meeting in its Recommendation 2/3 b) invited ICAO, in consultation with the World Meteorological Organization (WMO) and user organizations, to consider the need for harmonizing the criteria for issuance of SPECI and those for including change groups in TAF.

2.1.2	The AMOSSG/4 Meeting agreed that there was an operational need to harmonize these two sets of criteria but recognized that it was the SPECI criteria that represented the operational requirements. Therefore, the Secretary was requested to prepare an amendment proposal to the TAF change group criteria in order to provide the harmonization as required. The required changes consist of more detailed criteria for wind speed and visibility. Furthermore, the group may wish to agree that a requirement should be included in the SPECI criteria for the development or dissipation of cumulonimbus clouds which is currently a requirement for a change group in TAF.

2.1.3	In response to action a) of agenda item 5 of the summary of discussions of the AMOSSG/4 Meeting, the Appendix to this study note contains a proposal to amend the TAF change and SPECI issuance criteria for consideration by the group as a part of draft Amendment 74 to Annex 3.

2.2	Update of Attachment B to Annex 3 (ANC task 0403 a) 1, 4)

2.2.1	The group will recall that at the AMOSSG/4 Meeting a review was carried out concerning the operationally desirable accuracy of forecasts contained in Attachment E to Annex 3, which following the adoption of Amendment 73 in November 2004 became Attachment B.

2.2.2	The review of the attachment took place in two parts; within the AMOSSG concerning those forecast criteria associated with aerodromes, and within the World Area Forecast System Operations Group (WAFSOPSG) dealing with en-route forecasts. A further request, stemming from WMO, sought to ensure that the format of the attachment allowed for the forecast verification scheme that was being developed by WMO at that time. The group will recall that clarification was sought into the precise nature of the concerns expressed by WMO and requested Saad to provide some guidance on how the format of the attachment could be changed to accommodate such a verification scheme. In response to action a) of agenda item 7 of the summary of discussions of the AMOSSG/4 Meeting, a response from WMO was received by the Secretary on 19 October 2004 stating that no changes were required to the format of the attachment.

2.2.3	In response to action b) of agenda item 7 of the summary of discussions of the AMOSSG/4 Meeting, the Appendix to this study note contains a proposal to update the Attachment B of Annex 3 for consideration by the group as a part of draft Amendment 74 to Annex 3. The proposal simply combines the changes agreed by the AMOSSG/4 Meeting and by the WAFSOPSG/1 Meeting.

2.2.4	The group is further invited by the ANC to consider whether there is a need to establish a requirement for the accuracy of precipitation forecasts. It may be noted that currently the requirements specify the occurrence or non-occurrence of precipitation whereas there is no requirement concerning the intensity of precipitation. This is a longstanding task given to the Secretariat during the 136th Session of the ANC in 1994 which arose during the consultation process concerning Amendment 70 to Annex 3.

2.3	Desirability of greater accuracy in the first three hours of TAF and the limitation of the use of the PROB qualification (ANC task 0403 a) 2)

2.3.1	The group will recall that following action taken by the Air Navigation Commission (ANC) on a proposal to study the operational feasibility and desirability of requiring a greater accuracy in TAF during the first three hours of its validity period the group agreed during the AMOSSG/4 Meeting that further clarification was required. It was noted that one option was to remove the use of the "PROB" statement during this validity period and that it was unclear whether operational difficulties were being experienced either by overuse of PROB or the interpretation of PROB statements in differing ways by the operators.

2.3.2	In response to action c) of agenda item 7 of the summary of discussions of the AMOSSG/4 Meeting, study notes are invited from members of the group indicating whether any problems exist with the use of the term "PROB" or whether a general requirement exists for a greater accuracy in TAF over the first three hours of the validity period. If any problems are noted then appropriate actions should be discussed by the group.

2.4	TAF validity period (New task)

2.4.1	The group will recall the discussions at the AMOSSG/4 Meeting concerning difficulties being experienced by operators with the use of TAF for increasingly long flights. A proposed solution was that 24-hour forecasts should be issued with a lead time of 6 hours which would cater for the longest routes such as Manilla-Paris and Frankfurt-Santiago. However, some members of the group expressed the view that a 30-hour forecast with no lead time would be a more appropriate solution. The group agreed that the requirement for a 30-hour TAF would be the most appropriate long-term solution despite the need to amend the TAF code form to accommodate the duplication of validity times within the period of the forecast.

2.4.2	The group may wish to note that the European Air Navigation Planning Group (EANPG) at its 46th Meeting in Paris, 30 November to 2 December 2004, proposed an interim solution of providing 24-hour TAF with a 6 hour lead time in the EUR Region as the issuance times for TAF are subject to Regional agreements. However, the IATA position that only a single TAF was required for each aerodrome was noted by the meeting which would require a further solution to eliminate the need for the same aerodrome having both a short and long TAF. The meeting therefore agreed the following Conclusion:

Conclusion 46/25 —	ANNEX 3 PROVISIONS FOR ISSUANCE OF AERODROME FORECASTS FOR VERY LONG HAUL FLIGHTS

That ICAO consider a review of the Annex 3 provisions on the issuance and validity time for aerodrome forecasts (TAF) in order to meet new operational requirements for very long haul flights.

2.4.3	In response to action d) of agenda item 7 of the summary of discussions of the AMOSSG/4 Meeting, the Appendix contains a proposed amendment to Annex 3 stating a requirement for the introduction of 30-hour TAF to be issued every 6 hours for consideration by the group as a part of draft Amendment 74. The proposed amendment includes the date in all appropriate time groups.

2.4.4	The group may wish to consider the need for the requirement for more than one forecast being in effect for a single aerodrome, i.e. the continuation of the use of 9-hour TAF after the introduction of a 30-hour TAF with no lead time. This may also imply that the 30-hour TAF should be issued on a 3-hourly basis instead of the current 6-hourly basis. Further consideration could be given to the standardization of issuance times on a global basis which would remove the need for regional consideration. An alternative solution could be to simply introduce a requirement for each State to indicate in the air navigation plan (ANP)/facilities and services implementation document (FASID) whether a 9-hour TAF or 30-hour TAF will be issued for an international aerodrome, taking into account the traffic mix at that aerodrome.

2.4.5	The group is invited to consider the creation of an ad-hoc group to establish whether any appropriate additional amendments to Annex 3 are required on the basis of the above discussion. The group would be expected to work by correspondence with a view to developing proposals for inclusion in Amendment 75 to Annex 3 which would become applicable in 2010.

2.5	Visibility forecasting (ANC task 0403 a) 3)

2.5.1	During the review process of Amendment 73 to Annex 3 it was noted by the ANC at the 10th Meeting of its 164th Session that there was a need to consider whether there was a requirement to include the forecast of minimum visibility in TAF, in addition to prevailing visibility, when the visibility was forecast to vary in different directions. The group may wish to note that the required changes to Annex 3 would be straightforward and that the changes would make the annex more consistent. However, it could be considered to be of little operational use to issue such a forecast for most aerodromes owing to the difficulty involved in forecasting variable visibility over a period of up to 30 hours.

2.5.2	The group is invited to consider whether such forecasts are feasible and, if so, to agree on the nature of the most appropriate changes to Annex 3 for inclusion in draft Amendment 74.

2.6	Runway visual range (RVR) forecasting (ANC task 0403 b))

2.6.1	The group will recall that it is a longstanding task of the ICAO Secretariat to monitor the development of techniques for the forecasting of RVR which was originally formulated by the COM/MET/82 Divisional Meeting.

2.6.2	This issue has been studied by the MET/AOP PT in the EUR Region more recently and members of the group are invited to provide any updated information on progress made either in the context of the aforementioned group or within an individual State.

2.7	Miscellaneous editorial amendments to Annex 3

2.7.1	Three suggested editorial changes to the Annex 3 provisions were brought to the attention of the Secretariat during a review of the differences filed following the introduction of Amendment 73 in November 2004:

a)	the issuance of SPECI and amendments to TAF for the onset or cessation of thunderstorms only applies to those without precipitation, whereas those with precipitation should also be listed in the category where a change in intensity is considered;

b)	the consideration of present weather phenomena to be reported in trend forecasts currently allows a maximum of three elements to be reported for both elements involving precipitation and those without which could be misinterpreted to give a total of six elements. Therefore, clarification is required to specify that the total number of elements to be reported should not exceed three; and

c)	landing forecasts are currently intended to be provided as determined by regional air navigation agreement whereas the provisions in Annex 3 imply that the format of these forecasts is stipulated in the regional agreement rather than an indication of the aerodromes for which the requirement exists.

2.7.2	Proposed amendments to Annex 3 are contained in the Appendix for consideration by the group as forming a part of draft Amendment 74.

3.	ACTION BY THE GROUP

The group is invited to:

a)	consider the proposed changes to Annex 3 contained in the Appendix as a part of draft Amendment 74;

b)	consider whether there is a need to establish a requirement for the accuracy of precipitation forecasts;

c)	consider whether there is a requirement for a greater accuracy in TAF over the first three hours of the validity period and propose remedial action if necessary, and

d)	consider if it is feasible to forecast the minimum visibility in TAF in addition to the prevailing visibility when the visibility is forecast to vary in different directions.

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