World Meteorological Organization CAeM-XIV/INF. 4
COMMISSION FOR AERONAUTICAL METEOROLOGY Submitted by: Hong Kong, China
FOURTEENTH SESSION Original Language: English Hong Kong, China, 3 to 10 February 2010
LATEST DEVELOPMENTS OF WINDSHEAR ALERTING SERVICE FOR
THE HONG KONG INTERNATIONAL AIRPORT
CONTENT OF DOCUMENT:
A summary of the latest developments of the windshear alerting service at the Hong Kong International Airport.
; Information Paper
CAeM-XIV/INF. 4, APPENDIX
LATEST DEVELOPMENTS OF WINDSHEAR ALERTING SERVICE FOR THE
HONG KONG INTERNATIONAL AIRPORT
1.1 Due to the complex geographical environment in the vicinity of the Hong Kong International Airport (HKIA), low-level windshear and turbulence may occur at final approach and departure corridors in specific weather conditions, affecting the safe operation of landing/departing aircraft. The Hong Kong Observatory (HKO) works closely with the aviation stakeholders, including civil aviation authority, air traffic control, pilots and airlines, to enhance the windshear alerting service through the use of the latest technology and user awareness building.
1.2 This document summarizes the latest developments of windshear alerting service at HKIA.
2. LIDAR WINDSHEAR ALERTING SYSTEM (LIWAS)
2.1 A major technology advancement in the alerting of windshear at HKIA is the application of the Doppler Light Detection And Ranging (LIDAR) systems. Two systems are now working, each serving one of the two runways at HKIA. An automatic algorithm of using the LIDAR data to alert windshear, namely, LIWAS (LIDAR Windshear Alerting System), was put into operational use for arrival runway corridors of HKIA in December 2005. It is based on an innovative special scanning strategy of the LIDAR conceived by HKO, called the “glide-path scan”, to measure the headwind
profiles to be encountered by the aircraft along the glide paths of the runways.
2.2 Following the installation of a second LIDAR near the northern runway in 2006 and the subsequent relocation of the first LIDAR, originally sited near the middle of the airport, to the southern runway in 2008, it was found that the laser beams from the two LIDAR systems could become better aligned with the orientation of the runways of HKIA. In particular, the measurement of the headwinds along the southern runway, which is primarily used for departures, could be significantly improved. As such, the LIWAS algorithm has been enhanced to cover departure runways since September 2009. A special feature of the enhanced algorithm is the use of different windshear length scales for arrival and departure runway corridors. For example, for departing aircraft, wind changes over a distance of 4 km, even reaching the threshold of 15 kt, may not be regarded as significant because the aircraft is normally in full thrust and wind speed increase with altitude is generally expected to occur during take-off. For this reason, separate windshear alerts are given by LIWAS for arrivals and departures based on better performance of the algorithm using a different length scale (3 km) for detecting windshear for departures.
3. USER AWARENESS BUILDING
3.1 User awareness is an important element for enhancing the provision of weather services. Apart from the windshear briefings at the airlines, education of windshear and turbulence situations at HKIA has also been made through the publication of the booklet entitled “Windshear and Turbulence in Hong Kong – information for pilots”. This booklet was first published in 2002 and it
has been updated to the third edition in January 2010 through collaboration with the International Federation of Air Line Pilots’ Associations (IFAPLA) and The Guild of Air Pilots and Air Navigators (GAPAN). New materials include illustrations of the typical windshear and turbulence conditions at HKIA using LIDAR and radar observations, and clarifications for the users’ perception of windshear
based on flight data recorder (FDR) data. The new edition of the booklet is available for download from HKO’s Website on the windshear alerting service:
3.2 Moreover, a set of three windshear posters was published jointly by HKO, WMO, ICAO and IFALPA in 2008. They cover the common causes of windshear, warning and alerting methods, and the pilot’s rules of handling windshear. The posters are intended as training materials for
CAeM-XIV/INF. 4, APPENDIX, p. 2
pilots, air traffic controllers and aviation weather forecasters. They are available for download from the following Websites:
4. FUTURE DEVELOPMENTS
4.1 At HKIA, research is being conducted to explore the use of the LIDAR data and the Terminal Doppler Weather Radar (TDWR) data in the detection of turbulence. Apart from pilot reports, eddy dissipation rate (EDR) based turbulence intensity calculated from the FDR data of commercial aircraft and a meteorological instrumented fixed-wing aircraft of Government Flying Service in Hong Kong will form the basis in the development of the new turbulence detection algorithms.
4.2 Besides vertical wind profiles, the stability profile of the atmosphere can also be used to derive/diagnose the likelihood of terrain-induced turbulence and windshear. This could be based on temperature profiles continuously measured by the microwave radiometer at HKIA. New windshear warning rules utilizing the radiometer data are under development.
4.3 Apart from terrain-induced disturbances, there have been pilot reports of similar phenomena, albeit on smaller scales, associated with building structures at HKIA. The low-level wind effects due to these structures will continue to be studied. For instance, a short-range LIDAR with high spatial resolution will be deployed to observe the wind fluctuations downstream of the structures and calculate the turbulence intensity.
4.4 In addition to the continual semi-operational trial in collaboration with the Northwest Airline to uplink real-time TDWR and LIDAR windshear alerts to the cockpit, the feasibility of uplinking windshear and turbulence alerts in graphical format will also be explored. Prototype windshear and turbulence products in graphical format will be developed for future uplink applications in collaboration with the airlines.