Sydney Airport Wind Shear Encounter - 15 April 2007

At approximately 0923 UTC, on 15 April 2007 a Boeing 747 encountered low altitude wind shear in the final stages of an attempted landing on runway 16R at Sydney Airport in Australia. Available observations indicate the wind shear was associated with a microburst that developed over the airport as a line of high based showers and thunderstorms moved across the airport from the SW. There was only light intermittent precipitation reported at the airport during this period and there was no associated reduction in visibility. Fortunately the aircraft concerned successfully aborted the landing but the incident highlights the hazards to aviation associated with wind shear. The incident is also of interest because it resulted from a ‘dry microburst' in a coastal environment and the available observational data for this event allows an analysis that has not previously been possible in Australia.

For the period of interest radar data is available from the Sydney radar, located 40 km SW of the airport, and the Kurnell Doppler radar located 8 km SE of the airport. Anemometer data with a temporal resolution of 10 seconds is also available from a network of anemometers located on and near the airport. These data show the passage of a gust front ahead of the line of storms and then the development of the microburst near the threshold of runway 16R in the period shortly prior to the approach of the B747 aircraft. The microburst was present for just 4-5 minutes and was dissipating at the time the aircraft encountered the wind shear. The maximum divergence observed was at 092151UTC when the vector difference was 22 m.s-1 over a distance of 1.7 km and equates to a divergence of 12.9 x 10-3 s-1. This is substantially greater than the threshold of 10 ms-1 at ≤ 4 km used by Wilson et al (1984) to define a microburst (equating to a divergence of 2.5 x 10-3 s-1) and the mean difference reported by Hjelmfelt (1988) of 24 ms-1 over 3.1 km (equating to a divergence of 7.74 x 10-3 s-1).

The paper will present the observational data showing the evolution of the event. This includes Flight Recorder Data from the aircraft which shows the descent of the aircraft through the gust front and then the encounter with the decaying microburst.