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 takeoff 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.
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.
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 takeoff, 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 takeoff.
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.
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 takeoff 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.
The helicopter weighed close to its maximum permissible all up weight. The pilot reported that the power required to hover the helicopter in ground effect was about 23 inches manifold air pressure, which was close to the placarded limit. The flight manual data also indicated that the helicopter had insufficient power to hover out of ground effect in nil wind. The reported high power being used to achieve an in ground effect hover associated with the high density altitude conditions and the available flight manual performance data, indicated that the helicopter's engine was unlikely to have been capable of providing appreciably more power than that already being used.
The reported site information indicated that the helicopter would have needed to achieve a climb profile of at least three degrees. However, the available performance data indicated that there was unlikely to have been sufficient power available to depart from the in ground effect hover and achieve the required climb profile in nil wind. The helicopter's performance would have been adversely affected by the high relative humidity, which had the effect of further increasing the already high density altitude. Had the pilot consulted the flight manual or conducted a power check prior to landing on the pad, he may have realised that there was unlikely to have been sufficient power available to attempt the departure, or at least he could have planned the departure with a rejected takeoff in mind.
Neither the helicopter's flight manual, nor operator's operations manual provided climb performance data or guidance on expected power requirements for the helicopter to depart the hover and transition into forward climbing flight. Although the Civil Aviation Orders specify minimum performance requirements for aeroplanes, there are no similar requirements for helicopters. With no regulatory requirement for climb performance information to be provided by either the helicopter's manufacturer or the operator, the pilot had no documented guidance on the helicopter's expected performance in forward climbing flight. While it would have been prudent for the pilot to conduct a power check before commencing operations into or out of the helicopter landing site, there was no guidance provided by either the operator or helicopter manufacturer on required power margins. Therefore, a power check may have been of relevance to a pilot with experience in R22 limited power operations. However, the accident pilot's experience was not extensive, with a total flying time of about 173 hours. While he had accumulated 36 flying hours during the month prior to the accident he had only flown about 50 hours during the previous 16 months. It appears incongruous that, in accordance with the regulations and orders, the pilot had sufficient experience to transport passengers but insufficient flying experience to undertake mustering operations. While there was no documentary evidence detailing the pilot's initial training, there appeared to be some gaps in his knowledge with regard to operating the R22 helicopter close to its limits. The limited amount of flying he conducted in the 15 months between completing his course and joining the helicopter's operator may have also been a factor. He appeared to have been ill prepared to operate the helicopter in the high density altitude conditions of Northern Australia.
Although the task of carrying passengers from the station was not authorised by the helicopter's operator, the pilot reported that he was advised that the on-site experienced pilot was "in charge". The helicopter's operator was unaware of the requirement to conduct passenger flights, and in using the term "in charge" in relation to the on-site pilot, probably contributed to the pilot's belief that the on-site pilot was a nominated person who could authorise all flights. If the operator had been aware of the passenger flights, then more appropriate supervision of the pilot may have been provided. There appeared to have been a misunderstanding between the operator and the on-site pilot as regards to the use of the helicopter.
The pilot reported that he had not experienced any problems during the first takeoff from the site. He reported the wind as being gusty, averaging 15 kts and that there were thunderstorms in the area. With evidence indicating that there was probably little power available to depart the hover and achieve the required departure angle in nil wind, it was likely that the helicopter's performance was assisted during the previous takeoff by the wind conditions existing at the time. This may have lulled the pilot into a belief that the helicopter had sufficient power to attempt further takeoffs.
During the accident takeoff, the helicopter's main rotor RPM decreased. No evidence of a mechanical fault was subsequently found. The pilot reported that the wind was gusty and the humidity was high and increasing as storms built-up in the area. It was possible that the relative humidity had increased sufficiently to decrease the main and tail rotor performance or decrease the amount of power available from the engine. Alternatively, or in combination with the high relative humidity, the wind may have changed direction or lost strength during the accident takeoff. In either case, the pilot would have had to increase the collective pitch to maintain the departure profile. This may have resulted in the power required to drive the helicopter's rotor system exceeding the power available from the engine. As a result, the main rotor RPM drooped which reduced the lift being produced by the main rotor and the helicopter descended to the ground. Because the pilot had conducted the departure without considering the possible requirement to reject the takeoff, the area into which the helicopter descended was unsuitable for landing.
While the pilot was conducting the takeoff from Fossil Downs Station, the environmental conditions may have changed such that the power required to maintain the helicopter's departure profile exceeded the power available from the engine. As a result, the main rotor RPM decayed and the helicopter descended onto the ground. The pilot had not adequately assessed the power needed to conduct the takeoff and had used an inappropriate takeoff technique for the environmental conditions and helicopter weight. There was a misunderstanding between the operator and the customer as to the use of the helicopter. The pilot inadvertently believed he was authorised in accordance with the company operations manual to conduct the passenger flights. The helicopter's operator was unaware that the passenger flights were being conducted.
- The pilot was inexperienced.
- The density altitude and relative humidity were high.
- The wind conditions were gusty.
- There was no documented data or guidance available to the pilot to assist him in assessing the expected performance of the helicopter during the takeoff.
- The pilot did not adequately plan the takeoff to account for the weather conditions and helicopter landing site characteristics.
- The pilot used an inappropriate takeoff technique.
- The helicopter was probably at or close to maximum all up weight and had inadequate performance to complete the takeoff in nil wind.
- The weather conditions had changed since the first takeoff and did not assist the helicopter during the second takeoff.
As a result of this occurrence, the Bureau of Air Safety Investigation is investigating perceived safety deficiencies involving helicopter performance, pilot licensing and experience requirements.
Any recommendation issued as a result of this deficiency analysis will be published in the Bureau's Quarterly Safety Deficiency Report.
|Date:||03 February 1999||Investigation status:||Completed|
|Time:||1530 hours WST|
|Location:||9 km ENE Fossil Downs Station (ALA)|
|State:||Western Australia||Occurrence type:||Forced/precautionary landing|
|Release date:||24 September 1999||Occurrence category:||Accident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Robinson Helicopter Co|
|Type of operation||Charter|
|Damage to aircraft||Substantial|
|Departure point||Fossil Downs Station, WA|
|Departure time||1600 hours WST|
|Destination||Fitzroy Crossing, WA|
|Role||Class of licence||Hours on type||Hours total|