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METWSG/1-IP/3
/ METWSG/1-IP/3
9/11/07

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
7.2: / Study the need for the development of the criteria for the provision of warnings for rotor zones in terminal area

ASSESSMENT OF INCIDENCE OF ROTOR WAVES RESULTING IN AN AIRCRAFT INCIDENT

(Presented by Steven Albersheim)

SUMMARY
This paper presents information on work that has been conducted in the United States with regard to rotor waves and their affects on aircraft performance.

1.INTRODUCTION

1.1ICAO State letter 13 July 2007 (Ref: AN 10/22-IND/0715) noted that the Air Navigation Commission at the eighth meeting of its 175th Session agreed to the establishment of a study group to assist the Secretary to examine methods to improve the issuance, dissemination and formatting of SIGMETs and other meteorological warnings. The group also took over the responsibilities of the Low Level Wind Shear and Turbulence Study Group. One of the tasks identified in the State letter was to study the need for the development of criteria for the provision of warnings for rotor zones in the terminal area.

1.2The United States for many years through its Aviation Weather Research Program (AWRP) has studied various phenomena associated with turbulence and its cause, such as terrain induced turbulence. This information paper is being presented to share with the group various findings based on the research sponsored by the Federal Aviation Administration (FAA).

2.Discussion

2.1Current research in the United States

2.1.1Under the auspices of the AWRP, the FAA is supporting the NationalCenter for Atmospheric Research (NCAR) in examining terrain induced turbulence at at altitudes above 10,000 feet. This research has resulted in the Graphical Turbulence Guidance (GTG) product and version 3 (GTG3) that is scheduled for operational deployment in early 2010, which uses a suite of parameters to produce a forecast of turbulence associated with mountain waves.

2.1.2This discrimination capability of the automated mountain wave turbulence algorithms above 10,000 ft will be evaluated as part of the GTG3 Aviation Weather Technology Transfer (AWTT) process. However, the results of the evaluation cannot be used to determine the accuracy in the terminal area. Another approach is to use high resolution numerical models to predict waves, rotors, and turbulence in the terminal area. This approach has been shown to be able to recreate severe turbulence encounters at upper levels (Clark et al. 2000 JAS. Sharman et al. – ARAM 2004, Sharman et al. – ARAM 2006, Doyle 2005) and to reproduce rotors near the surface (Doyle and Durran 2002, Hertenstein and Kuettner – Tellus 2005). Therefore, numerical models may provide mountain wave turbulence warnings in the terminal area, but they need to be verified.

2.1.3The Desert Research Institute (as well as other institutions) through funding from the National Science Foundation is examining terrain induced turbulence. This program is known as the Terrain-induced Rotor Experiment (T-REX). This project studies the structure and evolution of low-level rotor waves with the aim of developing modeling capability to forecast rotor waves that may be a hazard to aviation.

2.1.4At the present time the information collected indicates that development of a modeling capability to support a forecast of rotor zones is not practical in the near term.

2.2Implementation issues for a warning message

2.2.1Terrain induced turbulence at aerodromes located in complex terrain is limited to a select number of aerodromes in the world. Documentation that supports aircraft accidents directly attributed to terrain induced turbulence is not sufficient to warrant any promulgation of a recommended practice for a warning message at this time.

2.2.2While the issues associated with terrain induced turbulence at aerodromes located in complex terrain are not to be ignored there is a need to establish priorities for where resources can be committed to support the work that would be required to provide a warning message of this nature.

2.2.3Besides the work that has been supported in research as described in section 2.1, the group needs to consider the complexities and the skill level required by a forecaster to adequately forecast a warning message for rotor zones. The complexity of the problem is immense and the skill level to provide this type of advance warning without numerical models and a sophisticated array of sensors would be limited. Based on past experiences with the issuance of SIGMETs by Meteorological Watch Offices, the majority of States do not have the resources available to them to provide this type of warning message. Therefore, the group should consider inviting the World Meteorological Organization to provide input and guidance on the science that would be required for a forecaster located in an aerodrome meteorological office to be able to provide a warning message and how it could be implemented on a global basis.

2.2.4While the group may question the merits of the issue and not necessarily reach a consensus, the one thing the group could consider is to support an effort to obtain statistics on the phenomena to better understand the global dimensions and magnitude of the problem. This would further help the group to determine whether there is a need to further pursue the development of criteria for the issuance of a warning message for rotor zones.

2.2.5To put this into perspective, U.S. National Transportation Safety Board provided a list of aviation accidents attributed (cause or factor) to mountain wave turbulence for the last 25 years within the United States. A total of 65 accidents occurred; however, 61 of them were small aircraft. The other 4 were large commercial aircraft, but only 1 was in the terminal area (Japan Airlines Boeing 747, 1993, Anchorage, AK). Thus there is a need for more information to determine whether there is a need for global requirement for this type of warning message.

3.Summary

3.1Current statistics and limited resources in the FAA AWRP may not be able to justify continuation of work that is focused on rotor zones in the terminal area.

3.2Existing accident statistics do not necessarily support a terminal rotor zone warning message based on data available to the United States.

3.3The group should independently collect information to determine the magnitude of the problem to determine if the issue is global in dimension or one that is unique to a few select airports.

3.4The group should consider inviting the WMO to provide guidance on the science and skill level of forecasters in aerodrome meteorological offices to even provide this information.

4.action by the metwsg

4.1The group is invited to note the information in this paper.

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