Preliminary report released 19 February 2008

On 7 January 2008, a Boeing Company 747 438 aircraft, registered VH-OJM, was being operated on a scheduled international regular public transport service between London, England and Bangkok, Thailand. The aircraft had 346 passengers and 19 crew on board, including four flight crew.

At about 0837 UTC, while the aircraft was at about 21,000 feet on descent to Bangkok International Suvarnabhumi Airport, the customer service manager (CSM) notified the flight crew that a substantial water leak had occurred in the forward galley.

Between approximately 0840 and 0852, cockpit indications showed a number of electrical bus and system failures that indicated alternating current (AC) buses 2, 1 and 3 were not powered. The status of AC bus 4 appeared normal and some systems were powered by batteries.

The captain's primary flight display, navigation display, and some other instruments were available in a degraded mode. Standby instruments and the aircraft's instrument landing system were also available. The crew conducted an approach to runway 01 Right in day visual meteorological conditions and the aircraft landed at 0907.

On 11 January 2008, the aircraft manufacturer issued a Multi Operator Message to operators of 747 400 series aircraft, containing advice and instructions for the inspection and repair of main equipment centre drip shields. The manufacturer is preparing an inspection and repair alert service bulletin on the same subject that is scheduled for release by May 2008.

On 11 January 2008, the aircraft operator issued a Cabin Standing Order and a Flight Standing Order requiring cabin and flight crews to treat and report abnormal water accumulation in galley areas.

On 29 November 2006, an Australian Army Black Hawk helicopter, A25-221, crashed during a training flight. The helicopter was attempting to land on HMAS Kanimbla located in international waters off Fiji. Onboard the helicopter were 10 army personnel - four aircrew and six soldiers. Of those onboard, eight survived and two were fatally injured.

The helicopter sank in deep water and the flight data recorder (FDR) was recovered in March 2007 after a salvage operation. The Australian Department of Defence was responsible for investigating this accident and appointed a Board of Inquiry. The Department of Defence requested ATSB assistance in the recovery of data from the FDR. The Executive Director of the ATSB approved the request. To protect the information supplied by the ATSB to Defence and investigation work undertaken to assist Defence, the ATSB initiated an investigation under the Transport Safety Investigation Act 2003.

The solid-state memory was successfully downloaded and a copy of the data file was provided to a representative from the Directorate of Defence Aviation and Air Force Safety.

Information publicly released by the Board of Inquiry is available on the Department of Defence website: http://www.defence.gov.au

Preliminary report released 8 February 2007

On 24 December 2006, the owner-pilot of an Auster Aircraft Company J1/A1 aircraft, registered VH-ALO, was intending to ferry the aircraft from a private airstrip at Nelson, Vic, to Akuna station S.A. The pilot was the sole occupant. At approximately 0930 Eastern Daylight-saving Time, the pilot commenced a take-off towards the west. Three people were standing between two hangars that were to the north of the airstrip, and they observed that the aircraft became airborne before it reached the taxiway leading from the hangars to the runway. When the aircraft was adjacent to the taxiway, it made a low-level right turn towards the hangars.

One witness, who was an experienced pilot, reported that the aircraft climbed suddenly just prior to striking a power line that was located on the airstrip side of the hangars. The aircraft then drifted over open space between the two hangers on a northerly heading; the left wing was seen to drop and the aircraft impacted the ground almost vertically. The pilot was fatally injured.

On 29 December 2006 at 1330 Western Daylight-saving Time, an Embraer EMB-110P2 Bandeirante aircraft, registered VH-FNP, departed Kununurra Airport, WA, enroute to Argyle. The aircraft was being operated on a charter flight with two pilots and one passenger onboard. The pilots later reported that, during climb out following take-off, while passing through 500 ft above ground level, the right engine lost power. The pilots confirmed the power loss, completed emergency procedures, that included shutting down the right engine, and returned to Kununurra Airport. There were no injuries to the flight crew or passenger and no damage to the aircraft.

Subsequent examination of the engine compressor turbine (CT) blades from the engine indicated that they had been subjected to a 'high temperature creep' event, leading to stress rupture of the CT blade assembly.

The investigation could not determine when the engine had sustained the localised high temperature heating of the compressor turbine components.

On 20 December 2006, a Kawasaki KH4 helicopter lost collective pitch control and impacted terrain while performing agricultural aerial spray operations approximately 21 km NE of Mount Gambier, SA. The helicopter was substantially damaged, but the pilot was uninjured. When the accident site was surveyed, the main rotor mast and main rotor blade assembly were found to have separated from the helicopter. They were located a short distance away.

Examination of the wreckage revealed that the helicopter's main rotor mast thrust bearing had failed catastrophically in flight. That bearing was a critical item for safe operation and continued airworthiness of the KH4. It supported the full weight of the helicopter and transferred thrust loads generated by the main rotor blades during flight.

The investigation was unable to conclusively establish the factors that led to failure of the mast bearing. No evidence was found of manufacturing or material defects. Nor was there any evidence of improper installation procedures or maintenance practice. Based on the inspection of aviation databases in Australia and North America, the main rotor mast thrust bearing failure appears to be an isolated event for the KH4-series helicopter.

Despite the low probability associated with a mast bearing failure of this type, the consequences of such an event could have been fatal for the pilot onboard. This report has been provided to Australian operators and maintainers of Kawasaki KH4 and Bell 47G3 series helicopters as a future alert for this type of occurrence.

A Saab 340B passenger aircraft, registered VH-UYA, experienced a left engine malfunction during the take-off roll at Mount Isa airport. In response to the abnormal engine condition, the flight crew rejected the take-off and shut down the left engine. When the engine was subsequently disassembled by the engine manufacturer, it was revealed that a single stage-four power turbine blade had fractured at the blade root. The liberated airfoil section caused secondary damage to the power turbine and exhaust sections. Metallurgical analysis of the fractured blade revealed that a pre-existing crack had been present at the blade root for a significant period of engine operation prior to the incident malfunction.

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.