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AMOFSG/7-IP/9
/ AMOFSG/7-IP/9
27/8/08

AERODROME METEOROLOGICAL OBSERVATION AND FORECAST STUDY GROUP (AMOFSG)

SEVENTH MEETING

Montréal, 9 to 12 September 2008

Agenda Item / 5: / Aerodrome observations

PROVISION OF INFORMATION ON CROSSWIND

IN SPECI, TAF AND TREND FORECAST

(Presented by C.M. Cheng)

SUMMARY
This paper raises the need for providing information on crosswind in SPECI, TAF and trend forecast, and presents a proposal to specify clearly the criteria under which such crosswind information should be provided.

1.  INTRODUCTION

1.1  An A320 jet with 130+ passengers on board was hit by extremely strong crosswind gusts while attempting to land at the Hamburg Airport on 1 March 2008. This near miss case exemplifies the need for information on cross-, tail- and headwinds, for both mean wind and gust for the aviation users, particularly the pilots.

2.  DISCUSSION

2.1  In the current ICAO Annex 3 / WMO Technical Regulations (Chapter C.3.1), indications of crosswind are provided in SPECI (Appendix 3, para. 2.3.2(d)), TAF (Appendix 5, para. 1.3.1(d)) and trend forecast (Appendix 5, para. 2.2.2(c)) under the following criterion:

“when the [surface wind is forecast to change] / [wind changes] through values of operational significance. The threshold values should be established by the meteorological authority in consultation with the appropriate ATS authority and operators concerned, taking into account changes in the wind which would:

1) require a change in runway(s) in use; and

2 indicate that the runway tailwind and crosswind components [have changed] / [will change] through values representing the main operating limits for typical aircraft operating at the aerodrome”.

2.2  Furthermore, under Amendment 74, Appendix 3 para. 4.1.5.2(c) specifies that in local routine and special reports and in METAR and SPECI,

“variations from the mean wind speed (gusts) during the past 10 minutes shall be reported when the maximum wind speed exceeds the mean speed by:

1) 10 km/h (5 kt) or more in local routine and special reports when noise abatement procedures are applied in accordance with paragraph 7.2.3 of the PANS-ATM (Doc 4444); or

2) 20 km/h (10 kt) or more otherwise”.

It is understood that this new provision is intended to address the effects of gusts on landing aircraft arising from turbulence associated with airport buildings when the application of noise abatement procedures renders the use of the runway concerned under crosswind/tailwind conditions.

3.  CONCLUSION

3.1  In the spirit of enhancing the safety of flights and support decision-making by pilots landing under unfavourable crosswind conditions, irrespective of the causes behind these conditions, it is recommended that indications of crosswind in SPECI, TAF and trend forecast should be clearly spelt out by making reference to the relevant crosswind operating limits of the major commercial aircraft types:

“when the crosswind [have changed] / [is forecast to change] through 40 km/h (20 kt), 50 km/h (25 kt) and other values of operational significance representing the main operating limits for typical aircraft operating at the aerodrome as established by the meteorological authority in consultation with the appropriate ATS authority and operators concerned”

4.  ACTION BY THE GROUP

4.1  The AMOFSG is requested to:

a)  note the content of this paper; and

b)  consider the proposal in para. 3.1 and, if supported by the group, formulate a draft amendment to Annex 3 for incorporation in Amendment 75.

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