In September 2023, a Westpac rescue Helicopter crashed into Waikato's Mt Pirongia during a rescue mission. Photo / Search and rescue Services Ltd
In September 2023, a Westpac rescue Helicopter crashed into Waikato's Mt Pirongia during a rescue mission. Photo / Search and rescue Services Ltd
In September 2023, a Waikato Westpac Rescue Helicopter crashed into Mt Pirongia.
The air ambulance was trying to get close to a patient who needed to be winched out of the bush.
The Transport Accident Investigation Commission released its final report today, confirming that the helicopter had been in a ‘vortex ring state’ when it crashed.
A Waikato Westpac Rescue Helicopter crash was caused by a phenomenon called a ‘vortex ring state’, an investigation has found.
The helicopter was trying to get near a patient who needed to be winched out of bush when it crashedin rural Waikato in September 2023.
The Transport Accident Investigation Commission (TAIC) has today released its final report on the incident, which found that the helicopter almost certainly entered a dangerous aerodynamic condition called a vortex ring state (VRS).
It may be the first-ever recorded accident found to have been directly caused by VRS, the commission said.
TAIC chief investigator of accidents Naveen Kozhuppakalam said VRS is a flight condition that causes a helicopter to lose lift and descend rapidly.
The accident scene where a Westpac Rescue Helictoper crashed in September 2023. Photo / Search and Rescue Ltd
The crash:
On September 19, 2023, the Westpac Rescue Helicopter flew from Hamilton to recover an injured person on Mount Pirongia. On board was a pilot, a crew member, and a paramedic.
The helicopter descended on the windward side of a ridgeline to prepare for a winch rescue. Suddenly, it lost height and crashed through trees into a steep, forested slope, coming to rest severely damaged just 7m upslope from a cliff.
The paramedic quickly attended to the patient and the pilot, while the crew member and paramedic prepared the patient for winch extraction.
The specific causes of the crash had not been confirmed until today.
Those on board survived a Westpac Rescue Helicopter crash in Mt Pirongia, in September 2023. Photo / Search and Rescue Services Ltd
What is a vortex ring state?
A vortex ring state is a dangerous flight condition that causes a helicopter to lose lift and descend rapidly.
Kozhuppakalam said VRS can take hold quickly and with little warning, especially in mountainous terrain, like that of Mt Pirongia.
Key factors that contribute to VRS include the helicopter’s trajectory, its descent rate, and forward speed, combined with its pitch attitude and the direction of the wind.
At the time of the crash, the pilot believed the helicopter was in level flight, but their attention was focused on the winch site rather than the instruments, Kozhuppakalam said.
“Meanwhile, the helicopter’s trajectory, descent rate and forward speed, combined with its pitch attitude and air flowing up and over the ridge, created the ideal conditions for VRS to take hold.”
Helicopter pilots receive training on VRS, but each helicopter model behaves differently.
The helicopter's flight trajectory. Photo / Search and Rescue Ltd
“In this case, VRS onset occurred just 291 feet [88.7m] above ground level – neither the height nor enough time to successfully recover," Kozhuppakalam said.
The report also found the helicopter’s flight manual contained very limited information about how to avoid VRS, or how to recover from it.
The helicopter’s manufacturer, Kawasaki Heavy Industries Ltd, has issued a safety notice and is updating its flight manual to include a recommended maximum rate of descent. It has also accepted TAIC’s recommendation to include specific VRS data in the manual.
VRS alerting systems are a new technology that can help pilots avoid entering VRS.
Kawasaki BK117 B-2, ZK-HHJ, the model involved in a crash on Mt Pirongia, September 2023. Photo / Search and Rescue Services Ltd
The report has also recommended the Civil Aviation Authority promote discussion at the International Civil Aviation Organisation on requiring VRS alert systems in new helicopters.
In New Zealand, TAIC recommends CAA promote awareness among helicopter pilots of VRS risks and advocate for more detailed information in all helicopter flight manuals.
Kozhuppakalam said all helicopter pilots need to clearly understand how VRS develops and how to avoid or recover from it.
“Flying in mountainous areas presents more challenges, and pilots need to use all available information, not just what they see outside the cockpit.”
