AMOSSG/5-SN No. 13

16/3/05

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FIFTH MEETING

Montreal, 11 to 14 April 2005

Agenda Item	6:	Aerodrome forecast requirements

USER REQUIREMENTS FOR TAF

(Presented by W. Woveris)

SUMMARY
This paper outlines the evolving user requirements for TAF and the need to review TAF provisions in Annex 3 accordingly.

1.	INTRODUCTION

1.1	The recent introduction of ultra-long range operations resulted in a new user requirement for longer TAF coverage. TAF provisions thus need to be reviewed to ensure TAF adequately support flight planning for international air transport. As this review is being conducted, it is suggested that other aspects of TAF provisions be considered, such as the issue of two different TAF for the same aerodrome, which is the source of some concern.

2.	DISCUSSION

2.1	TAF current provisions

2.1.1	The current provisions covering TAF production for aviation are basically more than 40 years old. At the time they were developed, the communication means available for transmission of aeronautical MET data were one of the major limiting factors.

2.1.2	As the decades passed, the requirements of operators for the number, validity period and availability of OPMET data have changed and led for example to the upgrade of the COM means (CIDIN, SADIS, etc.) to meet the requirements for transmitting the continuously increasing amount of data. The current COM is not the limiting factor any more, but now the TAF program itself does not meet the current operational requirements.

2.1.3	According to ICAO Annex 3, 6.2.6 the "period of validity of TAFs should be not less than 9 hours (short TAF,with a WMO data designator "FC") nor more than 24 hours (long TAF,with a WMO data designator "FT"); this period should be determined by regional air navigation agreement". The FASID parts of ANPs list aerodromes for which OPMET data is required in each ICAO Region.

2.2	Operational requirement

2.2.1	With the current increased operational flight times, i.e. 18 hours or even more (e.g. Manila-Paris, Santiago-Frankfurt, Singapore-New York), the requirements for TAF validity period has changed. TAFs used for flight planning should cover the ETA+/-1hr of the operation, not only for the destination, but also for all alternate airports. For the very long haul operations 18-hour or 24-hour TAF coverage would not be sufficient for the flight planning phase, which occurs 3 to 5 hours prior to departure. Some operators have indeed indicated a requirement for 30-hour TAFs.

2.2.2	The provisions for issuance and validity period of TAFs should be changed to meet the current operational requirements.

2.2.3	It is recognized that a format issue must be resolved due to the TAF covering more than 24H, to differentiate the last 6 hours from the first 6 hours of a 30H TAF. This would need a combined ICAO/WMO format amendment.

2.2.4	It is also recognized that TAF accuracy decreases over time and that the last hours of a 30H TAF may be less accurate. However, it is better to have a forecast, even less accurate, rather than none.

2.2.5	During the APANPIRG CNS/MET SG meeting in July 2004, it was mentioned that the US and Singaporean MET Service providers would test possible solutions for 30H TAF.

2.3	Other concerns

2.3.1	Many aerodromes issue the two types of TAF (FC & FT), with different issuance time, start of validity time and validity period. IATA does not require two different types of TAFs for any aerodrome. Depending on use and operational hours of an aerodrome either FC (9hr) or FT (24hr or 30hr) should be issued, not both. This creates operational problems and issues, such as:

a)	only one TAF type being amended, while the other remains the same;

b)	overlapping validity periods;

c)	only one type being available through some channels;

d)	non-harmonization of MET products between ICAO regions; and

e)	complexity and added costs.

2.3.2	To our knowledge, MET service providers, IFALPA and other stakeholders do not favour having different TAF products for the same aerodrome, to ensure consistency. For example, international aerodromes, listed in the RANP and supporting ultra-long range operations, would provide 30H TAF, other international aerodromes would provide 24H TAF. Non-international destination or alternates aerodromes not able to issue 24H TAF would issue 9H TAF (FC).

3.	ACTION BY THE AMOSSG

3.1	The AMOSSG is invited to:

a)	note the content of this working paper;

b)	request the US and Singaporean MET Service Providers to provide results from their test;

c)	review Annex 3 TAF provisions to satisfy user requirement for longer coverage; and

d)	consider Annex 3 TAF provisions ensuring aerodromes issue a single TAF type, promoting global harmonization.

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