The Robinson R22 helicopter was sent to Fossil Downs Station by the operator to conduct a small mustering assignment. As the operator's pilot was relatively inexperienced and not qualified to conduct mustering operations, the helicopter was fitted with dual controls so that an experienced and qualified pilot who was on-site could conduct the flying while the operator's pilot occupied the other seat. However, after the aircraft arrived at the station, the on-site pilot requested that the operator's pilot transport two passengers from the station to Fitzroy Crossing. Although the operator's pilot had insufficient hours to conduct mustering, he held a commercial pilot's licence and was qualified to carry passengers.
The pilot transported the first passenger from the helicopter landing site without incident. However, during the second departure, at about 15 ft and just as the helicopter was achieving translational lift, it sank back towards the ground. When the pilot increased the collective pitch in an attempt to regain the required departure profile, the low rotor RPM warning horn sounded and the rate of descent increased. The pilot reported that he checked that the throttle was fully open but the main rotor RPM continued to decay. The helicopter landed heavily and the main rotor blades clipped a tree. The pilot reported that as soon as it landed, he shut the engine down. The helicopter was extensively damaged but neither occupant was injured. The pilot reported that he flew the second flight's take-off into wind along a similar path to that flown during the previous passenger flight.
The maintenance organisation that repaired the helicopter reported that no mechanical fault was found that would have contributed to the accident. The accident was not subject to an on-site investigation by the Bureau of Air Safety Investigation.
Weather conditions
The pilot reported that the ambient temperature was about 37 degrees Celsius. He also reported that the humidity was high and increasing as storms were developing in the area. The wind was averaging about 15 kts from the south-east and gusting. The density altitude at the site, without factoring the relative humidity, was calculated to be about 3,000 ft.
The helicopter landing site
The pilot reported that he was using a southerly departure from the site to align with the general wind direction. The pilot reported that in the southerly direction, the helicopter landing site had an available length of about 50 to 60 m from the departure point with about 3 m high bushes at the departure end. There was also a small fence running east to west about 40 m from the departure point.
Helicopter performance
The helicopter weighed close to its maximum all up weight of 622 kgs. The helicopter's flight manual indicated that the calculated maximum weight to hover out of ground effect in nil wind, was about 605 kgs. The pilot did not consult the helicopter's flight manual for likely power requirements and power availability; nor did he conduct a power check prior to arriving at the helicopter landing site in order to ascertain the actual power available. While the Robinson R22 Flight Manual provided hover performance data, it did not contain performance data related to the expected climb performance of the helicopter during take-off, or in forward flight. The operator's operations manual did not provide guidance regarding power margins. There was no requirement under the existing regulations for information or guidance related to required power margins for departure or climb performance to be provided by either the helicopter's manufacturer or operator.
The pilot reported that the power setting required to hover the helicopter in ground effect was about 23 inches manifold air pressure, which was approximately the placarded limit manifold air pressure of 23.5 inches. The pilot could not recall the power indication during the accident take-off.
Ambient wind conditions can have significant and differing effects on a tail rotor equipped helicopter's performance. Engine power is delivered to a transmission system, which drives the main and tail rotors The power required to drive the transmission system is determined primarily by the amount of drag being produced by the rotors and the power available is determined by the power output of the engine(s). The difference between the power available and power required is known as the power margin. If the power required to drive transmission exceeds the amount of power available from the engine, then the main and tail rotor speed will decay, or droop. When the speed of the main rotor droops significantly, the main rotor loses lift and the helicopter descends. Wind blowing over a main rotor provides translational lift that can significantly reduce the power required to drive the helicopter's transmission system. Wind may also assist a helicopter to maintain heading, which also reduces the load demand on the transmission and therefore reduces the power required to drive the transmission. Conversely, a wind from an adverse direction may increase the load demand on the transmission and, in turn, the power required from the engine. Therefore, the wind may cause a net effect which, depending on its strength and direction, will reduce or increase the power required for a tail rotor equipped helicopter to maintain flight.
The density of air is affected by a number of factors including its moisture content. Relative humidity is the ratio of the amount of moisture in the air to the amount it is capable of absorbing at a given temperature. The greatest decrease in air density (increase in density altitude) due to moisture content will be at a high temperature. In general, as the density altitude increases, helicopter rotor and piston engine performance decrease. The performance data provided in the R22 helicopter's flight manual is only valid for nil-wind conditions and does not account for the adverse effects of high relative humidity.
Although the Civil Aviation Orders (CAOs) specify minimum performance requirements for single and multi-engine aeroplanes, there are no minimum performance criteria specified for helicopters.
Pilot Experience
The pilot had about 173 hours flying experience, of which about 83 hours were in command. All his flying experience had been gained on the Robinson R22 helicopter. Prior to joining the operator, he had flown about 14 hours during the 15 months since gaining his commercial (helicopter) pilot's licence in September 1997. He had been employed by the operator for less than one month and had accumulated just over 36 flying hours in that time. His initial training was conducted at several helicopter training schools in Queensland, and he reported that during the training, he had not experienced the helicopter being close to limits of power or practiced rejected departures and had not previously experienced main rotor RPM droop. He also reported that at the time of the accident, he was unaware of how to recover from a low rotor RPM condition. There were no available records related to his initial flying training, however, the pilot reported that he considered the training to be adequate. The operator conducted a proficiency check on the pilot about three weeks prior to the accident. The pilot's performance during the check was rated as satisfactory. About a month after the accident, the pilot attended a Robinson Safety Course where he flew with an experienced R22 helicopter instructor. The instructor reported that the pilot demonstrated an inappropriate take-off technique and that he required remedial instruction.
The Civil Aviation Orders impose a minimum requirement of 100 hrs as pilot-in-command before a pilot may conduct mustering operations. The Civil Aviation Regulations specify that a pilot may obtain a commercial (helicopter) pilot's licence, under certain circumstances, after a minimum total of 105 flying hours of which at least 35 hours are as pilot-in-command.
The company's operations manual required pilots to obtain authorisation from the Chief Pilot or a person nominated by the Chief Pilot before conducting any flights. The pilot reported that the Chief Pilot told him that the on-site pilot was "in charge". When he was requested to conduct the passenger flights, the pilot believed that the on-site pilot had the appropriate authority.