AMOSSG/4-SN No. 10

20/8/03

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FOURTH MEETING

Montreal, 15 to 18 September 2003

Agenda Item	7:	Aerodrome forecast requirements

TAF VALIDITY PERIODS AND ISSUANCE TIMES

(Presented by Pete Woveris)

SUMMARY
With the advent of Extended-Range aircraft, long flights require that TAFs be issued at least six (6) hours in advance of their valid times, and should be valid for twenty-four (24) hours. They shall supercede the previously-issued TAF upon the beginning of their valid, not issue, time.

Other TAFs should be issued at least three (3) hours in advance.

1.	The problem

1.1	To cover long flights, TAFs should be issued at least six (6) hours in advance of their valid times, they should be valid for twenty-four (24) hours, and they will supercede the previously-issued TAF upon the beginning of their valid time, not their issue time.

1.2	Many airlines now conduct long-haul international flights which are 14-18 hours in length, and longer flights are likely in the not-too-distant future. Current flights require planning at least two (2) hours in advance of departure, and most government regulations state that the forecast for the destination and alternate be valid for at least two (2) hours beyond the planned arrival time. Therefore, a TAF must be valid for at least 22 hours from its beginning time.

1.3	A second, related issue is the time of issuance of a TAF. These should be issued at least six (6) hours prior to the beginning of their valid time, sufficiently in advance for flight planning purposes as described above.

1.4	Other aerodromes serve as destinations for shorter international flights and need TAFs that are valid for only eighteen (18) hours. These TAFs should be issued with at least three (3) hours lead time. Nine (9) hour TAFs should similarly be issued with three (3) hours lead time.

1.5	It should be underscored that airlines need TAFs issued with sufficient lead time for flight planning purposes.

1.6	The Appendix presents an example of insufficient TAF validity period.

2.	Annex 3

2.1	Currently, Annex 3 includes the following:

2.2	"6.2.6 Recommendation : The period of validity of routine aerodrome forecasts should be not less than 9 hours nor more than 24 hours ; this period should be determined by regional air navigation agreement. (..) .Routine aerodrome forecasts (..) valid for 12 to 24 hours should be issued every 6 hours."

2.3	An amendment to this paragraph could be considered to address the issues mentioned in paragraph 1 of this Study Note.

3.	Action by the group

3.1	The group is requested to review the need to amend Annex 3 so that:

a)	24-hour TAF (valid for a 24-hour period) be issued as a requirement;

b)	The 24-hour TAF is issued at least 6 hours prior to the validity period (effectively covering a period from 6 hours to 30 hours after the issuance);

c)	The 18-H and 9-H TAFs are issued at least 3 hours prior to the validity period, and

d)	A TAF supercedes the previously-issued TAF upon the beginning of their valid time, not their issue time.

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