A serious incident over Sydney Harbour in April is a reminder of the distinctive hazard of helicopter wake turbulence.
A Robinson R44 helicopter carrying 2 passengers on a scenic flight experienced a sudden onset of turbulence followed by an uncontrolled descent as it entered the Parramatta River helicopter lane behind an EC120 helicopter.
The Australian Transport Safety Bureau (ATSB) found it was likely the R44 had entered the rotor wake from the EC120, which resulted in the control difficulties, an uncontrolled descent, a low–rotor speed warning and a forced landing.
The R44 landed at Cabarita Park, on the Parramatta River, in inner-western Sydney. It was able to take off again after the incident and returned to Bankstown Airport after a hover check.
The ATSB found the R44’s transponder had failed before the incident. The R44 had passed over Ryde Bridge out 9 seconds behind and slightly below the EC120 helicopter.
The ATSB report emphasised helicopter wake turbulence is larger and less predictable in its behaviour than for aeroplanes of the same weight.
Helicopter rotor vortices can descend, remain level or climb, and the duration of their persistence can increase significantly in conducive weather conditions. The United States Helicopter Safety Team website recommends remaining 3 rotor discs clear of a hovering or taxiing helicopter and allowing 3 nm and/or 2 minutes for the rotor wake from a preceding helicopter to dissipate.
The ATSB says vortex duration depends strongly on ambient weather conditions. A variance of 300% was observed on those days most conducive to vortex persistence and duration, compared with those observed on typical days.
After review of the draft report, CASA undertook proactive safety action to improve existing guidance about helicopter wake vortices in Advisory Circular 91-16. The updated advisory circular was released on 17 July 2025 and can be found at the link: AC 91-16 v1.2 – Wake turbulence.
