At approximately 1416 Central Daylight-saving Time on 15 Dec 2006, the flight crew commenced a take-off roll in a Boeing Company 737-400 aircraft, registered VH-TJH, on a scheduled passenger service from Adelaide, SA to Melbourne, Vic.

At a speed of approximately 50 kts, the crew reported an abrupt, uncommanded left yaw. Corrective action was applied, and the take-off was continued without further incident. The remaining flight was uneventful.

The flight crew subsequently reported that they did not notice any rudder pedal movement coincident with the uncommanded yaw and recalled that there was a gusting crosswind from the left during the take-off.

Data from the aircraft's Flight Data Recorder was recovered and downloaded by the Australian Transport Safety Bureau (ATSB) for review. That review indicated that the input to the aircraft rudder was not uncommanded and that the rudder pedals moved proportionally to the rudder surface deflection at all times. An examination of the aircraft by the aircraft operators' maintenance engineers did not identify any reason for the uncommanded yaw and the aircraft was released back to service. Additionally, there was no other aircraft traffic in the vicinity that may have generated wake turbulence in the immediate timeframe prior to the take-off.

While the nature of the uncommanded yaw could not be positively identified, it is likely that the event was related to an atmospheric disturbance or turbulence during the take-off.

The ATSB continues to monitor such reported uncommanded yaw events and has reported similar events in the past (see occurrence reports 200700035, 200500994 and 199703237 available on the ATSB website).

Preliminary report released 9 December 2006

The aircraft was reported to have impacted the ground during a flight to replenish the hopper for further spraying. The pilot was fatally injured.

During an approach into Cairns Airport, Qld in overcast conditions late on the morning of 2 December 2006, the pilot of a Piper Navajo aircraft, registered VH-BTD, lost control of the aircraft and entered an uncontrolled descent. Control of the aircraft was regained shortly before the pilot became visual below the cloud base, and the pilot continued to Cairns.

The loss of control was the result of the pilot's inexperience with respect to the effects of spatial disorientation and with flight in instrument meteorological conditions (IMC).

This occurrence reaffirms the potential for spatial disorientation, if not recognised and recovered from appropriately, to result in the loss of aircraft control.

On 27 November 2006, a Beechcraft King Air 200 aircraft, registered VH-XDB and carrying two crew and six passengers, was on a flight from Mount Hale to Perth, Western Australia. Shortly after commencing the decent into Perth airport, the right engine failed catastrophically.

An engineering examination of the failed Pratt and Whitney Canada PT6A-41 turboprop engine was performed and revealed that the first stage 'sun' and 'planet' gear set within the propeller reduction gearbox had decoupled from the power turbine. The decoupling allowed the power turbine to overspeed, which resulted in destruction and shedding of the turbine blades. Several blade fragments punctured the outer gas generator case.

A metallurgical examination of the failed first-stage gear set revealed that a mismatch in service histories between the sun gear and planet gears was the most likely contributor to the failure. The engine manufacturer had been alert to the occurrence of reduction gearbox distress due to gear mismatching at overhaul.

Following this incident, the aircraft operator initiated a review of their system of maintenance with respect to monitoring of life-limited engine components, for all PT6A engines in their fleet.

On 22 November 2006 at 0817 Eastern Summer Time, an Ilyushin Design Bureau IL-76TD (IL-76) aircraft, registered UR-BXQ, was reported to have entered the runway 28 stop way before becoming airborne while departing from runway 28 at Royal Australian Air Force Base Richmond, NSW. The aircraft was departing on a charter flight to Manila, the Philippines with 10 crew members on board.

A number of witnesses at various locations on the airport reported that the main wheels of the IL-76 did not lift off the ground until after the aircraft entered the stop way. However, the pilot in command of the IL-76 stated that the aircraft became airborne at about 250 m before the end of the runway.

From the available witness and flight crew reports, and the physical and recorded evidence, the investigation was unable to determine whether the aircraft entered the runway 28 stop way. The investigation could not reconcile the discrepancy between the recollection of events provided by the witnesses to the occurrence, and that of the pilot in command.

On 2 November 2006, the pilot of a Bell Helicopter Company 206A helicopter, registered VH-AAL, departed Coffs Harbour, NSW, on a private flight to a property located at Palmers Island, near Yamba, NSW. On board the 206A were the pilot and one passenger in the front left seat.

On arrival in the vicinity of Palmers Island, the pilot commenced a downwind turn into a strong quartering tailwind and the helicopter began an uncommanded right yaw. The pilot attempted to regain control, but the helicopter continued to yaw and to descend until it impacted the ground. The pilot and passenger sustained serious injuries and the helicopter was destroyed.

There was no evidence found of any mechanical or systems failures that may have contributed to the accident. The reported local conditions and nature of the loss of control were consistent with a loss of tail rotor effectiveness (generally referred to as LTE).

While a serviceable emergency locator transmitter was fitted to the helicopter, it had not been 'armed' prior to the flight and did not activate as a result of the impact.

On 15 November 2006, a Boeing Company 737-838 (737) aircraft was established on a visual approach to runway 01 at Brisbane, Qld. The Brisbane aerodrome controller (ADC) had issued a clearance for a vehicle driver to enter runway 01 to locate and remove debris that had been blown onto the runway strip. The ADC subsequently issued the pilot of the 737 with a landing clearance while the vehicle was still on the runway, anticipating that the vehicle would vacate prior to the 737 landing.

The ADC reported that he may have momentarily forgotten about the vehicle. An unidentified transmission, believed to have been made by the pilot of another aircraft waiting for departure, warned the ADC of the vehicle's presence. The ADC instructed the vehicle driver to vacate the runway and reissued a landing clearance to the pilot of the 737. There was a runway incursion.

Recent thunderstorm activity had resulted in unidentified debris being blown onto the active runways, requiring multiple entries for airside operations vehicles into the runway strip to locate and remove the debris.

The thunderstorm activity led to a situation where the ADC experienced a busy and complex workload for an extended period of time without a rest break. The ADC did not initially issue instructions to the vehicle driver, or adequately monitor the situation, to ensure that the vehicle vacated the runway strip so that separation was assured with the 737.

The investigation found a common misconception about the classification and reporting of runway incursion events. The ICAO runway incursion definition of an 'incorrect presence' does not preclude a presence being incorrectly authorised by an air traffic control clearance.

On 2 November 2006, at 1228 Central Summer Time a Boeing Company 767-338 aircraft, registered VH-OGL, departed Melbourne, Vic, on a scheduled passenger flight to Perth, WA. During the cruise climb, the crew reported that the Engine Indication and Crew Alerting System (EICAS) message displayed 'R OIL FILTER'. The crew initiated a descent and reduced the right engine thrust lever to idle. As the EICAS message remained illuminated, the crew shut-down the right engine, as required by the checklist, and diverted the aircraft to Adelaide, SA.

The operator's engineering personnel inspected the right engine magnetic chip detectors and found no evidence of debris. They also replaced the right engine oil scavenge filter and conducted an idle leak check. As no anomalies were found, the aircraft was returned to service.

Preliminary report released 31 October 2006

On 31 October 2006 at 1955 Eastern Standard Time, PA31-350 aircraft, registered VH-ZGZ, was on descent to Gladstone Airport, Qld when its radar track disappeared from the air situation display in the Brisbane Air Traffic Control Centre. Subsequently, the aircraft was found to have impacted terrain approximately 9 km south-east of Raglan, Qld. The pilot and two passengers were fatally injured. The aircraft was destroyed by impact forces and post-impact fire.

On 31 October, at approximately 1152 Eastern Daylight-saving Time, the pilot of a Bell 206 B3 helicopter, registered VH-KTR, was undertaking aerial feral animal culling operations with a feral animal shooter onboard. The pilot was lining the helicopter up for the shooter, when the engine power suddenly reduced to near idle. The shooter was able to throw his rifle out of the helicopter and brace for impact, in accordance with the Feral Animal Aerial Shooting Training (FAAST) procedures.

The helicopter descended into trees and came to rest supported by trees on the side of a steep hill. The occupants reported that the engine was still running after the helicopter came to rest, however, only at about idle power. The pilot then shut the engine down via the throttle. The pilot sustained facial and eye injuries while the shooter had minor injuries.

Examination and testing of the engine and components, and the fuel system was unable to determine what led to the sudden loss in power.

By following FAAST procedures, it is likely that the shooter reduced the danger to the pilot and to himself.