On 15 April 2007, a Boeing 747-400 operated by Qantas AW on a scheduled passenger flight from Singapore to Sydney was in the final stages of a daylight approach to land on Runway 16R at Sydney when at about 100 ft agl it encountered a significant and rapid change in wind velocity. The aircraft touched down heavily and the windshear warning sounded in the cockpit. The First Officer acting as PM carried out the prescribed windshear escape manoeuvre and subsequently made a second uneventful approach and landing. Two relief pilots were present on the flight deck during the occurrence. There were no injuries to passengers or crew and although some cabin panels fell down they were able to be re-fitted. The required heavy landing inspection subsequently confirmed that there was no aircraft structural damage.
An Investigation was carried out by the Australian Transport Safety Board who noted that at the time of the event, the airport had been under the influence a line of high-based thunderstorms associated with light, intermittent rain. It was concluded that “the aircraft was influenced by outflow descending from a high-based storm cell that developed into a microburst.”
The Non Volatile Memory from the aircraft Terrain Avoidance and Warning System (TAWS) system was downloaded and showed that there had been significant horizontal but little vertical shear present. The recorded airspeed had increased from 150 KCAS to 163 KCAS before falling rapidly to 135 KCAS during the next 7 seconds. This loss of airspeed had begun when the aircraft was over the runway at 111 feet agl just 8 seconds prior to touchdown. The absence of an airport low level windshear warning system (Low Level Wind Shear) was noted as was the fact that although pilots of aircraft operating on the reciprocal runway had previously reported moderate windshear to ATC and the surface wind conditions had been changing rapidly, this information had not been communicated to the occurrence aircraft. It was noted that although the aircraft had been only fitted with a reactive windshear alerting system, the fact it was a 'dry' microburst which had been encountered meant that even if the predictive system approved for the aircraft type had been available, it would have been unlikely to activate.
In response to this occurrence, the Bureau of Meteorology were noted to have begun a 'Sydney Airport Wind Shear Study' to assess options for providing low level windshear alerts and planned to complete that work by April 2010.
The Investigation concluded that the timing, location and characteristics of the windshear encountered were such that a hard landing had been unavoidable. Four 'Contributing Safety Factors were identified:
- Weather conditions in the Sydney Airport area were conducive to the development of low-level windshear associated with dry microbursts.
- There was no ground-based automatic low-level windshear warning system at Sydney Airport.
- The handling of wind and windshear-related information by air traffic controllers was inconsistent and resulted in the crew not receiving information that was relevant to the conditions they were likely to encounter during the landing approach.
- The aircraft encountered significant horizontal windshear associated with a dry microburst that commenced at about 120 ft radio altitude as the flying pilot began to flare the aircraft for landing.
The Final Investigation Report was published on 18 December 2009. The following Appendices are included within the Report:
- APPENDIX A: Bureau of metorology report
- APPENDIX B: Analysis by aircraft manufacturer
- APPENDIX C: Analysis by EGPWS manufacturer
- APPENDIX D: Sources and Submissions
No Safety Recommendations were made but it was considered that the review planned by the Bureau of Meteorology constituted an appropriate safety response.