| 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 12 Jul 2018, at about 1000 Eastern Standard Time, the pilot of a Robinson R44 helicopter took off with one passenger on board to conduct a few circuits[1] at Lethbridge Airport, Victoria, prior to departing the airport for a private flight.
The pilot conducted two circuits and on the third circuit, set up for an autorotation[2] to demonstrate to the passenger the rate of descent during the manoeuvre. The pilot selected a landing point 1/3 down the runway and established the helicopter at 70 kt, 600 ft above ground level (AGL). The pilot then partially rolled off the throttle to reduce the motor RPM and lowered the collective[3] to enter autorotation. The pilot was explaining the autorotation to the passenger when the low rotor RPM horn and light came on followed by a significant wobble and shake of the helicopter. The pilot checked the rotor RPM and it was about 70 per cent. The pilot initiated recovery by increasing collective and winding the throttle back on. This made little difference and at 300 ft, the pilot pitched the nose of the helicopter forward to increase RPM. Just prior to impact with the ground the pilot flared the helicopter and pulled full collective, however there was little rotor RPM left.
The pilot called for the passenger to brace and the helicopter landed somewhat level. As it skidded forward, the helicopter rolled to the left side and came to a stop. The helicopter was destroyed and the passenger sustained serious injuries.
Figure 1: R44 wreckage at Lethbridge Airport, Victoria
Source: Owner
Safety message
Practice of emergency recovery techniques such as autorotations should not be conducted with passengers on board. These carry an inherently elevated degree of risk. Additionally, passengers increase a pilot’s workload and can cause distractions. When conducting an autorotation; attitude, airspeed and rotor RPM should be the focus of the pilot’s attention. Practice autorotations are a dynamic manoeuver, increasing the potential to mishandle the helicopter. Two serious conditions associated with a mishandled autorotation are low rotor RPM stall and vortex ring state.
Safety Notice SN-10 on the Robinson Helicopter Company website states that, ‘No matter what causes the low rotor RPM, the pilot must first roll on throttle and lower the collective simultaneously to recover the RPM before investigating the problem.’
Safety Notice SN-24 Low RPM Rotor Stall can be Fatal and Safety Notice SN-22 Vortex Ring State Catches Many Pilots by Surprise, both detail recovery actions that require the collective to be lowered as part of the initial recovery actions.
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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- Circuit: The circuit is an orderly pattern that involves the pilot making approaches to a landing area, touching down and then applying power to take off again.
- Autorotation: Autorotation is a condition of descending flight where, following engine failure or deliberate disengagement, the rotor blades are driven solely by aerodynamic forces resulting from rate of descent airflow through the rotor. The rate of descent is determined mainly by airspeed.
- 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.