The Australian Transport Safety Bureau did not conduct an on-scene investigation of this occurrence.
At approximately 1330 Eastern Standard Time (EST) on 8 October 2004, a de Havilland Canada DHC-8-102 (Dash 8) aircraft, registered VH-TNW (TNW), with a crew of three and 18 passengers, encountered severe turbulence during approach to the Gold Coast Airport, Queensland. The aircraft was being operated on a scheduled passenger service from Brisbane to the Gold Coast.
The flight crew reported that conditions were quite rough with moderate turbulence during the flight. Approximately 25 NM from the Gold Coast Airport, at an altitude of 5,000 ft, the aircraft encountered turbulence that resulted in a wing drop, while operating with the autopilot engaged. The crew were then cleared by air traffic control (ATC) to descend to 4,000 ft and to reduce speed, as they were being radar vectored behind a Boeing Company 717 (B717) aircraft that had conducted a missed approach at the Gold Coast Airport due to encountering turbulence.
The crew of TNW reconfigured the aircraft for a flap 15 landing. They were then advised by ATC that they would be in front of the B717, were cleared for a visual approach and advised to contact the control tower. Passing through approximately 2,500 ft, the crew reported that they encountered a severe updraft that stopped the aircraft's descent. They then disconnected the autopilot and continued the descent. The crew reported that as the aircraft was passing through approximately 1,500 ft, they encountered severe turbulence, which required them to apply almost full control inputs to control the aircraft. The pilot in command then carried out a missed approach and the aircraft was reconfigured for a climb. During the missed approach, the number-1 engine `low oil pressure' warning light illuminated for a short time. The crew checked the cockpit indications and confirmed that the oil pressure was within limits.
They climbed the aircraft to 3,000 ft and manoeuvred for another approach. The pilot in command reported that during the downwind leg they observed that the water off the coast appeared to be `foaming'. He also reported a number of small water spouts present, and that there appeared to be a roll cloud forming ahead of the aircraft.
After landing, the crew advised the ground engineers that they had encountered severe turbulence. Following discussions with the operating company's base, a decision was made to ground the aircraft to allow a thorough engineering inspection. That inspection was to include flap over-speed and severe turbulence encounter inspections.
A review of the recovered data from the aircraft's flight data recorder revealed that, at a recorded altitude of 1,460 ft, the aircraft encountered a turbulence event that recorded +2.26 vertical `g'. At that point, the aircraft was banked to the left to 21 degrees. Almost immediately following this, the aircraft banked to the right to 20 degrees. The data also revealed that during the missed approach the engine torque values exceeded 100% for a period of two seconds and that the flap 5 limit speed of 148 kts was also exceeded.
The aircraft was not damaged during the turbulence encounter and none of the occupants were injured.
The pilot in command of the B717 reported that, when they had started descent, they were advised that the automatic terminal information service (ATIS) had changed. The new information that they received indicated that the temperature had dropped 7 degrees from the temperature that they had recorded just prior to starting the descent. He also reported that the conditions became very turbulent as the aircraft descended below 10,000 ft. While on approach, the conditions became very turbulent and he conducted a missed approach when the aircraft became unstable on the approach.
The general meteorological forecast for the morning of 8 October 2004 indicated that a trough line was moving across south-east Queensland. Coincident with the movement of this trough, a front was moving north along the New South Wales coast and was expected to move through south-east Queensland in the mid to late afternoon.
The Terminal Area Forecast (TAF) for the Gold Coast Airport, issued at 1104, indicated that the wind was from 300 degrees at 18 kts, with gusts to 30 kts. It further indicated that the wind was to change direction and strength at 1600. The TAF also indicated that moderate turbulence was expected below 5,000 ft from 1100 until 1700.
An amended TAF was issued at 1335, which indicated that the wind was from 160 degrees at 20 kts. This TAF also indicated that moderate turbulence was expected below 5,000 ft from 1300 until 1700.
Data from the automatic weather station (AWS) at the Gold Coast Airport indicated that the wind direction started to change from a north-westerly direction to an easterly and finally a south-easterly direction between 1230 and 1326. The recorded temperature also decreased from 34.6 degrees to 26.8 degrees in the same period. An aviation special weather (SPECI) report related to a change in wind direction and a drop of temperature of more than 5 degrees was issued by the Gold Coast Airport AWS at 1258. That information was not passed to the crew of the TNW.
A significant meteorological (SIGMET) warning of severe turbulence was issued at 1449 that covered the area surrounding the Gold Coast Airport. This turbulence was expected below 8,000 ft.
The passage of the front along the New South Wales coast was detected by automatic weather stations at Evans Head and Cape Byron. These stations did not have the capability to provide 1 minute updates to the data. Therefore they could only provide aviation routine weather (METAR) and SPECI reports.
SPECI data from Evans Head and Cape Byron stations indicated the passage of the front through those locations at 1025 and 1131 respectively.
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.
As a result of this and a number of similar occurrences, the ATSB is reviewing past investigations and data held by the Bureau covering safety issues relating to the communication of weather information to aircrews and between Airservices Australia and the Bureau of Meteorology and the safety action taken by these organisations to mitigate known problems in this area.
The ATSB has previously published reports of the investigations into occurrences that involved flight by regular public transport aircraft into convective weather and other weather situations where the availability of accurate weather information and communication of weather information to flight crews was a factor. For further information, readers are directed to ATSB occurrence investigations 200100213, 200105157, 200201228, 200301941 and 200304400 and associated safety recommendations. Copies of these reports are available from the ATSB website, or from the Bureau on request.
|Date:||08 October 2004||Investigation status:||Completed|
|Time:||1333 hours EST|
|Location:||Gold Coast, Aero.|
|Release date:||01 August 2005||Occurrence category:||Serious Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||de Havilland Canada|
|Type of operation||Air Transport Low Capacity|
|Damage to aircraft||Nil|
|Departure point||Brisbane, QLD|
|Departure time||1315 hours EST|