AERODROME METEOROLOGICAL OBSERVATION AND FORECAST STUDY GROUP (AMOFSG)

Transcription

1 AMOFSG/9-SN No /6/11 AERODROME METEOROLOGICAL OBSERVATION AND FORECAST STUDY GROUP (AMOFSG) NINTH MEETING Montréal, 26 to 30 September 2011 Agenda Item 5: Observing and forecasting at the aerodrome and in the terminal area 5.1: Observations REPORT OF THE AD-HOC WORKING GROUP ON THE CALCULATION OF CROSSWIND AND TAILWIND COMPONENTS WITH PARTICULAR REGARD TO THE INCLUSION OF GUSTS (Presented by Colin Hord, Rapporteur of AMOFSG/8 ad-hoc WG/1) SUMMARY This paper presents the conclusions of the ad-hoc team tasked with reviewing the calculation of crosswind and tailwind components with particular regard to the inclusion of gusts. 1. INTRODUCTION 1.1. At the eighth meeting of the Aerodrome Meteorological Observation and Forecast Study Group (AMOFSG/8), Action 8/3 led to the formation of an ad-hoc team comprising the following members Colin (Rapporteur), CM, Dennis, Herbert, Jan, Jarmo, Jun, Michel, Steve, Ndiwa and Carole. They agreed to work towards developing guidance material on the calculation of crosswind and tailwind components including gusts with the following steps: (7 pages) AMOFSG.9.SN en.doc a) review existing regulatory material; b) consider existing algorithms; c) propose suitable algorithms for use in guidance material; and d) report actions and next steps as necessary to the group.

2 AMOFSG/9-SN No A number of members provided valuable information leading to the summary presented in this paper. This group is especially indebted to the assistance of CM who provided significant input to this work. 2. DISCUSSION 2.1 Review of existing regulatory material for crosswind and tailwind At AMOFSG/8 a paper was presented that detailed a number of references to the existing ICAO regulatory material for crosswind and tailwind, these are listed at Appendix A. Since this meeting a further, but not exhaustive, review, was conducted and it was noted that: a) there is little information on how to calculate crosswind/tailwind including gusts in existing regulatory material; b) ICAO Annex 3 does not specifically regulate how to calculate crosswind/tailwind. It specifies the averaging period for gust, i.e. 3 sec (Appendix 3, ). A number of recommendations also touch on reporting of crosswind/tailwind [Appendix 3, a) 2) re SPECI; Appendix 5, d) 2) re TAF; Appendix 5, c) 2 re TREND forecast)]; c) ICAO Doc 8896 also contains the same recommendations on reporting of crosswind/tailwind as in Annex 3. Figure A7-5 depicts typical crosswind/tailwind limits; d) WMO Doc No. 8 does not appear to specify the algorithm of calculating crosswind/tailwind. Part 1, Chapter 5, states clearly the reasoning behind adopting 3-s average for gust; and e) WMO No. 731 Chapter 2.4 covers wind observation and the material therein basically comes from WMO Technical Regulation, WMO No. 8, WMO No. 488 as well as ICAO Doc It would also appear that few, if any, States have guidance information relating to the calculation of crosswind and tailwind with gust information. 2.2 Consider existing algorithms The group noted that the following algorithm could be used to derive crosswind and tailwind information.

3 - 3 - AMOFSG/9-SN No In order to relate these values in terms of crosswinds and tailwinds, an algorithm is used to take account of the runway alignment at any particular airport.. The algorithm used is as follows: Headwind: Wind strength x cos (wind direction-runway direction). A positive value denotes a headwind, and a negative value denotes a tailwind Crosswind: Wind strength x sin (wind direction-runway direction) A positive value crosswind is from the right, and a negative value crosswind is from the left e.g. Wind direction = 070 Wind strength = 20kts Runway = 09 Headwind = 20*cos (70-90) = (Headwind) Crosswind = 20*sin (70-90) = (from the left) In terms of algorithms for providing crosswind and tailwind including gust information it was noted that a number of suppliers of MET observing systems do provide a crosswind and tailwind calculation which in some cases make use of gusts. However since there is no agreed method for providing this information it appears that these systems use different algorithms for the calculation of crosswind and tailwind when using gusts. 2.3 Propose suitable algorithms for use in guidance material While reviewing this work it became clear that there were a number of alternative methods for including gusts when calculating crosswind and tailwind information Before reviewing these different options it should be noted that for Local Routine Reports and Local Special Reports the wind information is required to be averaged over a 2 minute period, with the gust information being the maximum recorded 3 second mean wind speed in the past 10 minutes. For SPECI the averaging period for wind information is 10 minutes, with the gust information being the maximum recorded 3 second mean wind speed in the past 10 minutes For SPECI it is also noted that where a marked discontinuity for wind (Annex 3 App 3 Para ) occurs only data occurring after the discontinuity shall be used for obtaining mean values, however the reporting of gust information is not subject to the marked discontinuity arrangement. Further consideration is required on how best to use gust information when a marked discontinuity information has occurred The alternative solutions that for the calculation of crosswind and tailwind when using gusts are described as follows: a) take the maximum 3 second mean in the past 10 minutes, and note the corresponding 3 second wind direction and use this information to calculate the crosswind and tailwind.

4 AMOFSG/9-SN No advantage: Easy to implement using existing sensors and systems. disadvantage: The 3 second mean wind direction at the time of the recorded gust value may deviate vastly from the 10 minute mean wind direction and could well be in an opposing direction to that of the mean crosswind or tailwind gust value. b) take the maximum 3 second mean wind speed in the past 10 minutes and note the 10 minute (or 2 minute if usage is required within the aerodrome) average mean wind direction; advantage: Easy to implement using existing sensors and systems. disadvantage: This would mean that a different crosswind or tailwind gust value would be provided depending on the averaging period. c) take the maximum 3 second mean wind speed in the past 10 minutes and note the 10 minute wind direction. Use these speed and direction values to resolve the crosswind and tailwind values; advantage: Easy to implement using existing sensors and systems. disadvantage: This would use the 10 min mean wind direction in calculating the crosswind and tailwind gust value for use within the aerodrome; and d) record all the maximum 3 second mean wind speeds along with their corresponding 3 second mean directions for the last 10 minutes. For each set of mean wind speed and direction firstly derive the crosswind and tailwind components. Then use the maximum wind speed and corresponding direction values in the past 10 minutes to derive the crosswind and tailwind gust components. advantage: This should ensure that the gust values are using the appropriate wind direction and will provide the highest values of crosswind and tailwind gust over the previous 10 (or 2) minute period. disadvantage: The calculation becomes more complicated, the reported crosswind and tailwind are calculated independently and they may occur at different times, thus the total gust calculated using the crosswind gust and tailwind gust may not equal the maximum 3 second mean wind speed over the period of 10 minutes As noted 2 members of the group supplied information describing how Met Observation systems display crosswind and tailwind information. It was noted that they use a similar approach to that as described in option B. However more guidance from Users is required to establish how this information is used i.e. is it used as guidance as to what the conditions are like currently and therefore likely to be, or is this information required to describe what has been the highest crosswind or tailwind that has occurred over the previous 2 or 10 minute period i.e the worst case, if this is the case then Option D would be required.

5 - 5 - AMOFSG/9-SN No In addition the cost of providing this information should also be reviewed, some of the options proposed require little or no modifications to existing systems and for that reason may be preferred. 3. ACTION BY THE GROUP 3.1 Noting that the group had limited input from the User community (IATA and IFALPA) it is proposed that further discussions are held to assess how best to provide crosswind and tailwind information and to understand the user requirement more fully. 3.2 Therefore, the group is invited to: a) request that the secretary ensures that this subject is tabled on the agenda of AMOFSG/9 in order that further discussion can take place on the various options provided; and b) prepare a paper following the discussions at AMOFSG/9 that can be presented to the ATMRPP (Air Traffic Management Requirements and Performance Panel) highlighting the issues associated with the provision of crosswind and tailwind when Gusts are included.

6 ATTACHMENT A REFERENCES TO HEADWIND, TAILWIND AND CROSSWIND IN ICAO DOCUMENTATION A. Annex 3 Chapter Wind shear warnings and alerts At aerodromes where wind shear is detected by automated, ground-based, wind shear remote-sensing or detection equipment, wind shear alerts generated by these systems shall be issued. Wind shear alerts shall give concise, up-to-date information related to the observed existence of wind shear involving a headwind/tailwind change of 30 km/h (15 kt) or more which could adversely affect aircraft on the final approach path or initial take-off path and aircraft on the runway during the landing roll or take-off run Recommendation. Wind shear alerts should be updated at least every minute. The wind shear alert should be cancelled as soon as the headwind/tailwind change falls below 30 km/h (15 kt). Appendix Recommendation. SPECI should be issued whenever changes in accordance with the following criteria occur: d2) indicate that the runway tailwind and crosswind components have changed through values representing the main operating limits for typical aircraft operating at the aerodrome; Appendix Recommendation. The criteria used for the inclusion of change groups in TAF or for the amendment of TAF should be based on the following: 2) indicate that the runway tailwind and crosswind components will change through values representing the main operating limits for typical aircraft operating at the aerodrome; Appendix Surface wind The trend forecast shall indicate changes in the surface wind which involve: c2) indicate that the runway tailwind and crosswind components will change through values representing the main operating limits for typical aircraft operating at the aerodrome. B. PANS ATM Doc 4444 Chapter SUSPENSION OF INDEPENDENT PARALLEL APPROACHES TO CLOSELY-SPACED PARALLEL RUNWAYS Independent parallel approaches to parallel runways spaced by less than m between their centre lines shall be suspended under certain meteorological conditions, as prescribed by the appropriate ATS authority, including wind shear, turbulence, downdrafts, crosswind and significant meteorological conditions such as thunderstorms, which might otherwise increase ILS localizer course and/ or MLS final approach track deviations to the extent that safety may be impaired.

7 A INFORMATION FOR ARRIVING AIRCRAFT At the commencement of final approach, the following information shall be transmitted to aircraft: a) significant changes in the mean surface wind direction and speed; Note. Significant changes are specified in Annex 3, Chapter 4. However, if the controller possesses wind information in the form of components, the significant changes are: Mean headwind component: 19 km/h (10 kt) Mean tailwind component: 4 km/h (2 kt) Mean crosswind component: 9 km/h (5 kt) Chapter Noise abatement shall not be a determining factor in runway nomination under the following circumstances: e) when the crosswind component, including gusts, exceeds 28 km/h (15 kt), or the tailwind component, including gusts, exceeds 9 km/h (5 kt) Reduced runway separation minima shall be subject to the following conditions: c) tailwind component shall not exceed 5 kt -END-