| Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation. |
What happened
On 14 June 2020 at approximately 1600 Central Standard Time, the pilot of a Robinson R22 helicopter was conducting mustering operations on a property near Tindal Airport, Northern Territory.
The pilot was attempting to herd a number of cattle into a yard, which was proving difficult as the cattle were not moving as required. The pilot decided to land the helicopter behind the cattle to encourage them to move forward, and selected a landing site on a graded road bordered on either side by trees. The pilot was confident that the dust would be minimal in the selected landing area and planned to use a direct-to-the-ground approach to reduce the potential of creating a dust cloud and a possible brownout condition.[1]
As the helicopter descended below 3 ft, an excessive amount of dust was raised from the landing area and the helicopter immediately became fully enveloped by the dust cloud. The pilot elected to reject the landing and commenced a climb, but as all visual references were lost and there were obstacles close by, the pilot quickly decided to put the helicopter on the ground as soon as possible.
The pilot lowered the collective[2] and the helicopter contacted the ground with an amount of left lateral movement resulting in a rollover. The helicopter came to rest on its side sustaining substantial damage (Figure 1). The pilot was uninjured in the accident.
Figure 1: Helicopter post-accident
Source: Operator
Pilot comments
The pilot commented that normally a request for ground personnel assistance to herd the cattle would have been made, however as one of the ground personnel was recently injured the pilot was reluctant to ask for help. The pilot also advised that the mustering job had been delayed to late in the day, and therefore self-induced time pressure to complete the task existed. On reflection, the pilot advised the ATSB that these considerations may have influenced the decisions made on the day.
Brownout condition
The brownout phenomenon can lead to accidents during helicopter take-off and landing operations in arid / desert terrain. Dust clouds created by the rotor downwash during near-ground flight can result in the pilot losing visual reference. This increases the risk of the helicopter colliding with the ground and other obstacles, as well as dynamic rollover due to sloped, uneven terrain or uncommanded aircraft movement due to spatial disorientation.
There are several factors that affect the probability and severity of brownout:
- aircraft weight / rotor disk loading
- soil composition
- wind
- approach speed and angle.
Safety message
This accident highlights the importance of selecting a suitable landing area and the best approach path and landing technique for the surrounding environment. This includes consideration of appropriate escape routes when faced with an unexpected situation such as a brownout condition. Pilots should also always maintain situational awareness of environmental factors like wind direction, obstacles and surface conditions in order to mitigate risk and avoid an unfavourable situation.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
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- Brownout condition: is an in-flight visibility restriction due to dust or sand in the air. In a brownout, the pilot cannot see nearby objects which provide the outside visual references necessary to control the aircraft near the ground. This can cause spatial disorientation and loss of situational awareness leading to an accident.
- Collective: 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.