What happened
On the afternoon of 21 July 2018, a Robinson R4-4 Raven II helicopter, registered ZK-HTB, was performing a private flight from Wanaka Aerodrome to the Upper Estuary Burn Valley. The pilot was traveling to a lodge to meet friends. During the flight, the aircraft's position reports indicated a significant increase in groundspeed, rising from 86 knots to 96 knots, while the altitude decreased from 1,772 feet to 1,454 feet.
Shortly after the final position report near Stevensons Island, the aircraft disappeared from tracking. A search operation involving local helicopters, New Zealand Police, and the Royal New Zealand Navy eventually located the wreckage on the lake floor at a depth of 47 meters. The pilot, the sole occupant of the aircraft, was killed in the crash.
The investigation
Investigators from the Transport Accident Investigation Commission (TAIC) examined the wreckage and recovered various components, including pieces of the main rotor blades and cargo. The examination of the main rotor hub revealed that the pitch links had failed and the teeter stops were crushed. Notably, both main rotor blades had rotated approximately 180 degrees into an upside-down position.
Physical evidence at the crash site, including score marks on the underside of the rotor blades and damage to the aircraft's canopy and window framing, suggested the aircraft experienced extreme forces. The investigation also noted that the helicopter's weight and balance were within safe limits at the time of departure, and the aircraft had been maintained according to the manufacturer's schedule.