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METWSG/1-SN No. 8
/ METWSG/1-SN No. 8
22/10/07

METEOROLOGICAL WARNINGS STUDY GROUP (METWSG)

FIRST MEETING

Montréal, 20 to 22 November 2007

Agenda Item / 7: / Amendments to provisions related to wind shear warnings and alerts
7.3: / Consider the need to provide information on low-level temperature inversion either in a specific warning or in the supplementary information appended to local reports and METAR/SPECI

NEED FOR THE PROVISION OF INFORMATION ON LOW-LEVEL TEMPERATURE INVERSION

(Presented by the Secretary)

SUMMARY
This study note discusses the need to provide information on low-level temperature inversion.

1.INTRODUCTION

1.1The group may wish to note that this task was originated by the European Air Navigation Planning Group(EANPG), through Conclusion 47/32,calling for ICAO to consider amending Annex 3 — Meteorological Service for International Air Navigation to include the low level temperature inversion information as a meteorological related safety hazard at aerodromes. This conclusion wassubsequently endorsed by the Air Navigation Commission(ANC) at its 172nd Session.

1.2The group may also wish to note that when discussing this issue, the EANPG agreed that low-level temperature inversion had a detrimental effect on aircraft performance during take-off and landing and suggestedthat there could be two possibilities for reporting such phenomena: as a specific warning (similar to wind shear); or as supplementary information appended to local reports and METAR/SPECI.

1.3In this regard, the group may wish to notethat this issue has been regularly addressed over the years by the ANC. In 1986 during the review of the replies received to a letter to selected States and international organizations on the possibility of using data extracted from flight data recorder to determine the frequency, occurrence and magnitude of deviations from the standard temperature lapse rate, the International Air Transport Association (IATA)called for the encouragement of better reporting of marked temperature inversion.However, the ANCfelt that there was not enough information to propose provisions for inclusion in Annex 3. Furthermore,it was noted that there was still confusion between inversions and deviations from the standard lapse rate. The group may wish to note that at that time the ANC agreed that provisions in Annex 3 were not required and that guidance material on the provision of information on significant deviations from the standard temperature lapse rateshould be included in theManual of Aeronautical Meteorological Practice (Doc8896).

1.4Subsequently, in 1994 the issue wasreaddressed during the preliminary review of an amendment proposal to Annex 3 regarding the provision of information on weather phenomena hazardous to low-level flights. In this regard, in reply to a query from the International Federation of Air Line Pilots’ Associations (IFALPA),the ANC feltthat there was no need including temperature inversions in AIRMET/GAMET, since they were mostly a problem in terminal areas and that guidance material had been included in Doc 8896.

1.5Regarding the guidance issued, the group may wish to note that the Manual of Aeronautical Meteorological Practice (Doc8896)contains some guidance related to temperature inversion. In particular, it relates temperature inversions to wind shear for which a requirement to issue warnings already exists. Furthermore,an appendix entitled“An operational wind shear and inversion warning system for Helsinki-Vantaa Airport”(Appendix 13 refers) which provides extensive guidance providing an example on how to deal with this phenomenon. It should be noted that for temperature inversions,there is an alarm limit; when the limit value is exceeded a warning message is issued and reported in the automatic terminal information service (ATIS)broadcast.The warning message is also shown on the airport terminal data network.

1.6The group may wish to concur that the situation has not changed and that temperature inversions need not to be subject to a stand-alone warning provided that warnings related to the accompanying wind shear are issued.Furthermore, the group is invited to agree that specific, local warning systems such as the one described in Doc 8896 is satisfactory to cover operational requirements and that there is no need to draft SARPs at this stage. Therefore, the group may wish to agree to the following action:

Action agreed 1/..Provision of information on low-level temperature inversion either in a specific warning or in the supplementary information appended to local reports and METAR/SPECI
That the sub-task be deleted from the work program of the study group.

2.ACTION BY THE METWSG

2.1The METWSG is invited to:

a)note the information in this paper; and

b)decide on the draft action proposed for the group’s consideration.

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