On 22 June 2009, an Airbus A330-300 being operated by Qantas on a scheduled passenger flight from Hong Kong to Perth encountered an area of severe convective turbulence in night Instrument Meteorological Conditions (IMC) in the cruise at FL380 and 10 of the 209 occupants sustained minor injuries and the aircraft suffered minor internal damage. The injuries were confined to passengers and crew who were not seated at the time of the incident. After consultations with ground medical experts, the aircraft commander determined that the best course of action was to complete the flight as planned, and this was uneventful.
An Investigation was carried out by the ATSB. The flight crew stated that when approaching the coast of Borneo, the aircraft was in clear air with no indication of cloud either visually or on the weather radar. The lights of Kota Kinabalu and other coastal cities in the region were visible below the aircraft as it approached the coast of Borneo, which suggested, in conjunction with the absence of distant weather radar returns from the area where the encounter occurred suggested that the cloud did not extend into the lower levels where the radar installed would have detected precipitation. The severe turbulence began as the aircraft entered cloud. The flight crew believed that the cloud was probably composed of ice crystals, due to the noise of particles impacting the aircraft, the outside air temperature of -50 °C, and the high reflectivity of the aircraft strobe lights when within the cloud.
An examination of Flight Data Recorder (FDR) data showed significant disturbance in a number of the atmospheric conditions affecting the flight during the severe turbulence event. The disturbance lasted for about 20 seconds, and included large variations in both wind velocity and air temperature. Wind speed reduced from a stable 20 knots prior to the encounter to 5 knots before increasing to 38 knots and again stabilizing. Wind direction varied up to 75° either side of 125° true. Temperature was a stable -51°C before the encounter then rose to -46°C before dropping and stabilising at -52°C as the encounter ended. During that time, the aircraft experienced a vertical acceleration of between -0.48 and +1.59g with an almost instantaneous change in wind direction of about 150° at the point of maximum negative g. The recorded variations in g over a very short period of time confirmed the severity of the turbulence.
The Investigation noted that ice crystals are a form of water that is least well detected by aircraft weather radar and was not detectable by the radar fitted to the incident aircraft. It was also noted that as the event occurred at night with no moon, there had been little opportunity for the crew member maintaining a visual lookout to see the weather. The Operator advised the Investigation that it intends to upgrade the weather radar fitted to its A330 fleet to increase the capability to detect convective turbulence. Two other related but minor safety issues were identified during the investigation:
- At the time of the occurrence, the aircraft commander was returning a publication to the flight deck library which required them to move their seat to the fully aft position. Whilst in this position, turbulence caused the contents of the library to be deposited in their lap which, combined with the position of their seat, temporarily restricted their access to the flight controls.
- The turbulence also caused the flight deck door manual latch to engage which, until one of the operating flight crew were able to vacate their seat and reset the lock, temporarily prevented access to the flight deck by the resting flight crew. The aircraft operator considered that this had probably occurred because the latch had been incorrectly stowed.
The aircraft operator advised the Investigation of their intention to address both issues.
The Final Report of the Investigation was released on 30 June 2010 and may be seen in full at SKYbrary bookshelf: Aviation Occurrence Investigation AO-2009-029 Final
No Safety Recommendations were made.