User Needs

The best starting point for developing an operational concept is to review the issues and needs raised by the future users of the AOAWS. User needs were developed during meetings held in Taipei in 1996, 1997 and 1999. Organizations represented in the meetings included the Taiwan Civil Aeronautics Administration (CAA), Far Eastern Transport (FAT), China Airlines, EVA Air, Air Force Meteorological Center, Central Weather Bureau (CWB), TransAsia, Hwa Hsin Airlines, Formosa Airlines and U-Land Airlines.

Chun-Ming Jou (So-So), visiting engineer from the CAA in Taipei,
is working on the MDS display at the AOAWS lab in Boulder.

Major issues considered in the development of AOAWS concepts:

  1. Convective windshear (including microburst) detection in the terminal areas has higher priority than other advanced aviation weather products.
  2. Terrain-induced windshear and turbulence in the terminal area has the second highest priority.
  3. Thunderstorm hazards in the terminal area are important followed by thunderstorm hazards in the domestic enroute region and lastly in the FIR region. Thunderstorm hazards include windshear, turbulence, lightning, and to a lesser extent, icing.
  4. Knowledge of airport surface winds and ceiling and visibility are necessary for safe operations. Better forecasts of those conditions are highly desired.
  5. For flight planning, accurate information (current and forecast) of winds and temperature aloft are required.
  6. The users agreed that better weather detection and forecasts accuracy for all aviation weather information is desired.
With this in mind, a number of considerations for AOAWS development were reviewed and accepted. AOAWS design considerations include:
  1. The windshear systems – Low–Level Windshear Alert Systems (LLWAS) and the Windshear Processor (WSP) – should have a high Probability of Detection (POD) and low False Alarm Rate (FAR).
  2. If more than one sensing system is used for hazards detection, the resulting alert information should be based on an integrated approach.
  3. Terminal alert information should be concise to keep the controller workload low.
  4. The AOAWS should use standard terminology for describing weather phenomena. For example, products such as flight categories should use standard definitions for IFR, VFR, etc., and standard terms should be used for turbulence and windshear. Event intensities should also be given using standard terminology.
  5. Alert conditions should be reserved for operationally significant (safety critical) events.
  6. Crosswind shear may be an operational problem at some airports, particularly at CKS and Kaohsiung.
  7. Vertical windshear is thought to be a common occurrence at CKS. More research is needed to understand this phenomenon and determine whether it is an aviation hazard.
The windshear alert generation strategy should be consistent with FAA and other established systems. For example:
  1. Alerts should be provided, where possible, out to 3 nm on approach and departure.
  2. Alert update rate should be approximately 60 seconds or faster.
  3. The alert corridor around the runways should be 1/2 nautical mile wide on either side of the centerline to account for windshear event movement.
  4. Windshear alerts should be provided as gains or losses in wind speed (knots).
  5. The minimum windshear alert threshold should be 15 knots.
  6. The minimum microburst threshold should be 30 knots (windspeed loss).