Low level wind shear has been identified as an aviation hazard which has caused or contributed to a significant number of aircraft accidents. In order to protect aircraft from deadly wind shear, the Federal Aviation Administration (FAA) uses a network of sensors, collectively called the Low Level Wind Shear Alert System (LLWAS). The LLWAS has undergone several advancements in both design and algorithmic computation. The latest deployment, known as the Low Level Wind Shear Alert System-Network Expansion (LLWAS-NE), consists of additional sensors to the original LLWAS network, providing better coverage of the airfield. In addition, the LLWAS-NE is capable of providing runway-oriented wind shear and microburst alerts with loss and gain values. The alerts from LLWAS-NE will be integrated with those from the Terminal Doppler Weather Radar (TDWR) at most LLWAS-NE locations.
An analysis was undertaken at Orlando (MCO) and Dallas/Fort Worth (DFW) International Airports to assess wind shear alerts produced by the TDWR/LLWAS and ITWS/LLWAS integration algorithms. By very careful comparison of TDWR base data with LLWAS data for cases where PIREPS indicated overwarning, we were able to identify an LLWAS sensor overspeed problem. Based on the Orlando experience, we suggest that ongoing assessment of the LLWAS-NE should use both LLWAS-NE and TDWR base data when possible. Comparing both data sets also will facilitate optimization of LLWAS parameters used in the computation of alerts. Examples of such comparisons using data from DFW and MCO will be presented.
The current TDWR/LLWAS integration algorithm was developed on the notion that both systems have correctly measured a valid wind shear event but are getting different results due to the different measurement methods. If both systems are measuring the wind shear event correctly, the current approach is probably adequate. However, if one system has sensor failures (as was the case at MCO), a much greater use of overall domain information seems necessary. At times, identifying problems which arise from the sudden failure of an individual sensor to produce correct wind measurements is very challenging. The paper will discuss some options for greater use of Doppler data in the real-time integration algorithm to validate LLWAS alerts when there is no confirming TDWR alert or the TDWR is indicating a much lower strength event (especially when the TDWR has a good viewing angle for the event).
* This work was sponsored by the Federal Aviation Administration. The views expressed are those of the authors and do not reflect the official policy or position of the U.S. Government.
+ Opinions, interpretations, conclusions and recommendations
are those of the authors and are not necessarily endorsed by the United
States Air Force.
The 8th Conference on Aviation, Range, and Aerospace Meteorology