Collision with terrain involving a Robinson R22, VH-HUA

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Collision with terrain involving a Robinson R22, VH-HUA 93 km SE of Mount Isa, Queensland, 20 March 2015 ATSB Transport Safety Report Aviation Occurrence Investigation AO-2015-033 Final – 10 June 2015 Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Publishing information Published by: Australian Transport Safety Bureau Postal address: PO Box 967, Civic Square ACT 2608 Office: 62 Northbourne Avenue Canberra, Australian Capital Territory 2601 Telephone: 1800 020 616, from overseas +61 2 6257 4150 (24 hours) Accident and incident notification: 1800 011 034 (24 hours) Facsimile: 02 6247 3117, from overseas +61 2 6247 3117 Email: atsbinfo@atsb.gov.au Internet: www.atsb.gov.au © Commonwealth of Australia 2015 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this publication is owned by the Commonwealth of Australia. 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Addendum Page Change Date › 1 ‹ ATSB – AO-2015-033 Collision with terrain involving a Robinson R22, VH-HUA What happened On 20 March 2015, at about 1140 Eastern Standard Time (EST), a Robinson R22 helicopter, registered VH-HUA, departed from Stanbroke Station for a private flight to Devoncourt Station, Queensland. On board were a pilot and one passenger. The main fuel tank was filled to capacity prior to departure, with 68 L of fuel. While en route between the two stations, the pilot was assessing the water available for stock by overflying water holdings. At about midday, while about 500 ft above ground level, the helicopter approached a gorge. To assess the water quantity in the gorge, the pilot conducted a descent to about 100 ft and slowed the helicopter to a hover. As the pilot shifted his focus outside, the rotor revolutions per minute (RPM) decreased, the low rotor RPM warning horn sounded and the helicopter commenced descending. The pilot immediately lowered the collective1 and turned the helicopter away from the higher gorge walls in an attempt to increase forward speed and rotor RPM. He was unable to regain sufficient rotor RPM and the helicopter continued to descend. The right skid landed heavily on uneven ground, followed by the left skid. The main rotor then collided with a rock and the helicopter rolled onto its right side. The pilot and passengers exited the helicopter and were not injured. The helicopter sustained substantial damage (Figure 1). Figure 1: Damage to VH-HUA Source: Aircraft operator Local conditions The temperature at the time was about 42 °C and the elevation of the area was about 1,000 ft above mean sea level. The pilot reported the wind was southerly at about 10-15 kt, but the gorge was sheltered and the wind in the vicinity of the accident was calm. 1 A primary helicopter flight control that simultaneously affects the pitch of all blades of a lifting rotor. Collective input is the main control for vertical velocity. › 2 ‹ ATSB – AO-2015-033 Pilot comments The pilot reported that his attention was momentarily diverted outside checking the water, when he would normally be watching the gauges and monitoring the rotor RPM. He usually operated without a passenger on board, so the extra weight of the passenger had reduced the helicopter’s performance, particularly its ability to maintain a hover out of ground effect. Power required and power available A number of factors related to the power required and the power available may have contributed to the decaying main rotor RPM during a hover out of ground effect.2 These factors include density altitude, take-off weight and the wind component. • Density altitude. Increasing density altitude adversely affects helicopter performance through the combined effects of reducing the power available and increasing the power required. Considering elevation and temperature, and barometric pressure in the area, the density altitude at the accident site would have been around 4,000 ft. High relative humidity would have had the effect of further increasing the density altitude. • Operating weight. Increasing the helicopter weight increases the power required. The greater lifting force demanded of the main rotor, and the requirement to counter the associated increased torque effect3 with the tail rotor, both contribute to an increased power requirement. The weight of the helicopter at the time of the accident was less than the maximum permitted operating weight, but reduced the ability to hover out of ground effect. • Wind component. A nil wind component increases the power required because of the diminished or delayed influence of translational lift.4 The following references discuss factors affecting helicopter performance, and provide some guidance to pilots regarding the associated considerations: • A ‘Good Aviation Practice’ booklet titled Helicopter Performance, produced by the Civil Aviation Authority (CAA) of New Zealand. The booklet is available via the CAA website: www.caa.govt.nz/safety_info/good_aviation_practice.htm • The Federal Aviation Administration (FAA) Helicopter Flying Handbook (chapter 7 deals with