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The Agusta/Bell 47G-2A1 helicopter departed from Maroochydore airport at about 1420 Eastern Standard Time (EST) on a solo navigation exercise. The pilot intended to track via Somerset Dam, Kenilworth, Nambour and return to Maroochydore under the Visual Flight Rules (VFR), with an expected enroute flight time of about 1.9 hours. A flight plan was not submitted to Airservices Australia by the pilot. However, a flight notification form was retained by the company for search and rescue (SAR) purposes. Shortly before take-off, the pilot was cleared by the Maroochydore Tower controller to track direct to Somerset Dam via The Big Pineapple initially at 1,500 ft above mean sea level (AMSL).

Air Traffic Services (ATS) primary radar intermittently tracked the helicopter at a position 7 NM northeast of the accident location about 40 minutes after departure. The primary "paint" ceased about that time and location. A witness reported seeing the helicopter near the northern side of Mount Archer at about 1515 EST and flying in a manner consistent with the pilot experiencing controllability difficulties. A subsequent aerial search located the wreckage at a position about 1 NM right of the direct track from Maroochydore to Somerset Dam and on the north-north-eastern slope of Mount Archer. The helicopter sustained severe impact damage. The pilot received fatal injuries.

Some notes containing pre-flight navigation planning calculations and small pieces of the perspex cockpit bubble were found several hundred metres before the accident site. The notes contained navigation calculations that did not take into account the forecast enroute winds. Personnel at the flight training school did not recall discussing at length the forecast weather conditions with the pilot and, in particular, they did not recall briefing the pilot about the forecast mountain waves prior to the navigation exercise. The personnel at the flight training school also reported that helicopter pilots had been flying throughout the day in the Maroochydore region without experiencing any controllability difficulties induced by the forecast and actual strong winds.

The ATSB investigation team did not attend the accident site but viewed video footage and police photographs of the wreckage. The video footage had been recorded by the search and rescue helicopter crew at the time the wreckage was located. Damage to the helicopter structure was extensive and the tail boom was severed. According to the search and rescue helicopter crew, the helicopter's emergency locator transmitter (ELT) did not activate. The pilot also carried a portable ELT but it was damaged during the impact and did not activate.

The pilot held a Student Pilot Licence and a Restricted Private Pilot (Aeroplane) Licence. At the time of the accident the pilot had accumulated a total of 72.5 flying hours in helicopters, including 21.5 hours on Bell 47G helicopters. The pilot's aeroplane flight time records were not available to the investigation.

At the time the accident report was compiled, the pilot toxicology and autopsy results were not available. Consequently, the investigation was unable to comment on whether the pilot's performance was adversely affected by any pre-existing physiological condition.

There were no known maintenance deficiencies and the helicopter was considered capable of normal flight prior to the accident.

A Bureau of Meteorology (BOM) area forecast, issued at 1338 EST on the day of the accident, indicated isolated severe turbulence and mountain waves below 9,000 ft. The BOM examination of the available data indicated that the wind between 1,000 ft and 5,000 ft above ground level (AGL) in the Mount Archer area was constant with height at about 250 degrees True in the range 25 to 30 kts. The surface wind speed was estimated to be around 15 to 20 kts with frequent gusts in the range 25 to 30 kts. The relative orientation of the ridge and wind direction were conducive to mountain waves and possible rotor effects (see Attachment A) to the northeast of Mount Archer. The helicopter impacted terrain on the north-north-eastern slope of Mount Archer. The search and rescue helicopter pilot's report of actual meteorological conditions in the vicinity of the accident site was consistent with the BOM forecast.

Initial video and photographic evidence indicated that the helicopter probably encountered severe turbulence from mountain waves or rotors in flight while approaching the lee of Mount Archer. The evidence suggested that the main rotor blades may have severed the tailboom approximately 1 m forward of the tail rotor assembly. This accident signature is consistent with excessive blade flapping. The evidence indicated that a divergence of the main rotor blade from its normal plane of rotation probably occurred as a result of severe turbulence generated by mountain wave or rotor activity, and a main rotor blade contact with the tailboom and cockpit area ensued, resulting in a loss of control of the helicopter.

It is also possible that the collective lever friction may have been overcome by the severe turbulence that caused the non-powered collective lever to suddenly drop. The collective lever drop would have induced a sudden nose down attitude and this may have caught the pilot by surprise. The pilot may have instinctively and rapidly applied aft cyclic to correct the aircraft's attitude. The rapid application of aft cyclic in this situation may have been sufficient to induce main rotor blade contact with the tailboom.

A further discussion of mountain wave phenomena is provided in Attachment A.


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