ASN Wikibase Occurrence # 223778
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| Date: | Thursday 28 June 2018 |
| Time: | 12:05 |
| Type: |  Robinson R44 Raven II |
| Owner/operator: | |
| Registration: | |
| MSN: | |
| Fatalities: | Fatalities: 0 / Occupants: 4 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Mt Conner, NT -
 Australia
|
| Phase: | Landing |
| Nature: | Passenger - Scheduled |
| Departure airport: | Ayers Rock-Connellan Airport, NT (AYQ/YAYE) |
| Mt Conner, NT | |
| Confidence Rating: |  Information verified through data from accident investigation authorities |
On 28 June 2018 at 1125 Central Standard Time, the pilot of a Robinson R44 Raven II helicopter departed for a return charter flight from Connellan Airport, Northern Territory, to Mt Conner, NT. The originally scheduled, larger aircraft, a Bell JetRanger experienced an unserviceability, and the Robinson R44 was allocated to the flight. There were three passengers on board. When the pilot departed Connellan Airport, the helicopter was at its maximum gross weight of 1134kg. This was the pilot’s first trip to Mt Conner.
Mt Conner, known as Attila to the Pitjantjara people, is a mesa standing 2818 feet above mean sea level, and 984 feet above ground level. On the day, a high-pressure weather system pushed the pressure altitude slightly lower to around 2600 feet. There was a light wind from the east-northeast. The flight to Mt Conner took just under 40 minutes, using 25kg of fuel on the way. The landing weight of the helicopter at Mt Conner was 1109kg. According to flight manual performance charts, the helicopter was capable of performing an out of ground effect hover at the landing site.
The pilot wasn’t comfortable with his first approach and correctly aborted it. The second approach felt better to the pilot and he flew the helicopter at a 300 feet/min rate of descent towards the western ridgeline. At 40 KIAS, 50 feet above and 10 m from the ridge, the pilot noticed a sudden increase in rate of descent. The pilot thought he had entered vortex ring state (VRS) and initiated a technique known as the Vuichard Recovery. This involves using full power, tail rotor thrust and lateral cyclic to move the helicopter sideways out of the downwash of the main rotor. The Vuichard Recovery technique had not been taught to the pilot, nor was his proficiency in its use tested.
At 40 knots, the helicopter’s downwash flows out behind the aircraft and VRS will not develop. The VRS recovery initiated did not arrest the rate of descent. The aircraft was now in a state whereby the power required to arrest the rate of descent exceeded the engine power available. Cancelling the lateral movement to avoid sideways contact with the ground, the pilot initially lowered the collective before pulling full collective to reduce the rate of descent.
Pulling collective increases the pitch on the main rotor blades to increase lift and increases the power demand on the engine. The low RPM light and horn activated as aerodynamic drag on the main rotor blades exceed the available power from the engine, slowing the rotor; a situation known as overpitching. The aircraft landed heavily in a level attitude 20m to the right of the helipad. The skids absorbed the impact and there were no injuries.
Sources:
https://www.atsb.gov.au/publications/occurrence-briefs/2018/aviation/ab-2018-087/
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 08-Apr-2019 13:16 | Pineapple | Added |
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