Standard Practices and Procedures in the Provision of Wind Shear and Microburst Alerts

METWSG/2-SN No. 13 27/3/09

METEOROLOGICAL WARNINGS STUDY GROUP (METWSG)

SECOND MEETING

Montréal, 19 to 21 May 2009

Agenda Item 6: Wind shear and turbulence warnings 6.1: Low-level wind shear detection along the approach/take-off paths

STANDARD PRACTICES AND PROCEDURES IN THE PROVISION OF WIND SHEAR AND MICROBURST ALERTS

(Presented by Steven Albersheim)

SUMMARY This paper presents information on Air Traffic Control Services procedures in the provision of wind shear and microburst alerts for over 100 aerodromes.

1. INTRODUCTION

1.1 Current procedures used by ATC for the provision of microburst and wind shear alerts to aircraft on approach and take-off paths do not include forecasts or predictions. The alert information disseminated is real-time only. These procedures are used at over 100 aerodromes in the United States that are equipped with Low Level Wind Shear Systems (LLWAS) or a combination of LLWS with Terminal Doppler Radar.

1.2 The responsibility of ATC in relaying weather alerts to the pilot is confined to repeating the message directly as displayed from the automated alert system. The controller is required to repeat the message as shown on the automated alert display without alteration.

(3 pages) 0b22068d4dc9384717cb8e5edf6c2c8d.doc METWSG/2-SN No. 13 2

2. DISCUSSION

2.1 For clarification, consider the Integrated Terminal Weather System (ITWS) Microburst Prediction algorithm which is part of the ITWS suite of algorithms. Microburst predictions with a lead time of up to two minutes in advance are determined by using TDWR upper level tilts and other environmental data to monitor the growth of thunderstorms. The output of the algorithm is not passed along directly to ATC for dissemination as an alert message, but contributes to the generation of the final alert product which is passed to the pilot from the controller.

First, the microburst predictions are merged with the detections by allowing an existing wind shear detection (15, 20, or 25 knots) to be increased to a 30 knot microburst if the two events are co-located. The result of the merged products is then used to determine the final alert messages that are distributed to ATC for dissemination to the pilots.

The ITWS Microburst Prediction algorithm enhances the current detections to provide an advanced warning of a hazard up to two minutes in the future. The alerts are issued to the controller as current conditions; there is no distinction between alerts detected by the detection algorithm, and wind shear alerts that have been increased to 30 knots in strength based off of the prediction algorithm output. These alert strength increases are not considered to be forecasts or predictions. The lead time of two minutes is intended to account for the time the wind shear (15, 20, or 25 knot loss) is detected by radar and the time that an aircraft encounters it, in which time it could grow in intensity quickly.

2.2 The distinction between wind shear warnings and wind shear alerts are discussed in section 7.4 Wind shear warnings and alerts, of ICAO Annex 3 Chapter 7. Wind shear warning is defined as having a human element, while wind shear alert is specific to “…wind shear (is) detected by automated, ground-based, wind shear remote-sensing or detection equipment…”. Wind shear alerts are also noted to be “…information related to the observed existence of wind shear…”; therefore, including a status of “FORECASTED” with the message would be inconsistent with this clarification.

2.3 Providing additional status about the automated alert, such as being corroborated by a pilot, would be introducing a human element and result in an alert message that is no longer automated. If provided, the status would be subject to the same one minute or less update rate as the other alert information. That is, each human provided status of “REPORTED” by a pilot would have to be tracked for expiration in order to be associated with the automated alert message. This method of operating is not practical and is inconsistent with both the definition of automated alerts, and the current ATC procedures on disseminating alert messages.

2.4 In consultation with ATC there is no operational requirement to qualify an alert as FORECAST or REPORTED based on automated wind shear alert system. The microburst and wind shear alerts provided are never a forecast, nor are they identified by the controller as being corroborated by a pilot.

3. RECOMMENDATION

3.1 In that it is identified in the discussion that algorithms that provide wind shear alerts are not forecasts, the group should not consider any additional or changes in phraseology to provide a forecast as part of an automated wind shear alert. 3 METWSG/2-SN No. 13

3.2 In that it is identified in the discussion that automated wind shear alerts do not include a human element, the group should not consider any additional or changes in phraseology to identify an automated wind shear alert as being corroborated by a pilot.

4. ACTION BY THE METWSG

4.1 The METWSG is invited to:

a) note the information in this paper; and

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

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