| 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 the morning of 27 March 2018, a Robinson R22 helicopter landed at Delamere Station, Northern Territory (NT) to conduct a refuel from the drum stock.
At about 0730 Central Standard Time (CST), after the refuelling was complete, the pilot proceeded to take-off from the station. During the take-off, the downwash from the main rotor blade spun the fuel pump around the top of the fuel drum resulting in the fuel hose hooking over the helicopter’s skid. The fuel hose subsequently pulled the helicopter to one side causing dynamic rollover.[1] The helicopter collided with the ground resulting in substantial damage (Figure 1).
Figure 1: Robinson R22 post-accident, in the vicinity of the fuel drum
Source: Operator
Safety message
The pivoting of the helicopter with the skid in contact with the fuel hose, and subsequent loss of control is consistent with the phenomenon known as dynamic rollover.
Once started, dynamic rollover cannot be stopped by application of opposite cyclic[2] control alone. Even with full opposite cyclic applied; there is not sufficient control authority to arrest the roll once it is developed and the main rotor thrust vector and its moment serves to accelerate the roll. Quickly reducing collective[3] pitch is the most effective way to stop dynamic rollover from developing.
This occurrence serves as a reminder for pilots to never hover close to fences, sprinklers, bushes, runway lights or other obstacles a skid could catch on.
The R22 Pilot's Operating Handbook includes a safety notice (SN-9) which provides advice about how to avoid dynamic rollover situations.
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.
__________
- Dynamic rollover: A rolling tendency, when close to the ground. For dynamic rollover to occur, some factor has to cause the helicopter to roll or pivot around a skid or landing gear wheel until its critical rollover angle is reached.
- Cyclic: a primary helicopter flight control that is similar to an aircraft control column. Cyclic input tilts the main rotor disc, varying the attitude of the helicopter and hence the lateral direction.
- 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.