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Analysis

Summary

The Terminal Area Forecast (TAF) provided information to the crew that moderate turbulence was likely to be encountered during the flight. The meteorology information provided no warning of severe turbulence until after the flight had landed at the Gold Coast. The TAF that the crew had used indicated that the change in wind direction and strength at 1600 would signify the passage of the front over the Gold Coast.

The turbulence encountered during the Dash 8's initial approach and the visual observations reported by the crew of a roll cloud and water spouts, were consistent with the aircraft having encountered the leading edge of the frontal zone. This was about 2 hours earlier than forecast. The indications from the weather stations at Evans Head and Cape Byron confirmed that the front was moving to the north faster than expected. However, the severe turbulence associated with the front could not be determined from those weather stations and was therefore unexpected.

The drop in temperature of 7 degrees provided the pilot in command of the B717 with an indication that conditions at the Gold Coast Airport were changing earlier than forecast. This temperature drop was also recorded by the automatic weather station at the Gold Coast Airport. While the drop in temperature cannot by itself indicate the degree and/or severity of turbulence likely to be encountered, it did indicate the arrival of the front.

As the aviation special weather report issued at 1258 was not passed to the crew of TNW, they were not in a position to appreciate that the passage of the front over the Gold Coast Airport was earlier than expected. The crew were aware that the B717 had encountered turbulence in the area of the Gold Coast Airport, but were not fully aware of the severity of that turbulence.

During the missed approach, the flap 5 limit speed was exceeded for a short period of time. At the time, the crew were likely to have been preoccupied with the low oil pressure warning and maintaining control of the aircraft due to the turbulent conditions. The overspeed did not result in damage to the aircraft. The extreme roll rates encountered by the aircraft could have given the perception that the aircraft rolled to unacceptably high roll angles, however the data recovered from the flight data recorder revealed that the roll angles encountered were within normal operating parameters.

The changes recorded in vertical `g' readings were indicative of a severe turbulence encounter. The decision by the crew to conduct a missed approach due to the turbulence was in accordance with normal operating procedures.

 
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