What happened
On 9 March 2013, a Robinson R66 helicopter crashed in the North Island's Kaweka Range, resulting in one fatality. While flying under visual flight rules in uncontrolled airspace, the aircraft experienced a phenomenon known as a mast bump. This event caused a main rotor blade to strike the fuselage, leading to the structural breakup of the helicopter in mid-air. At the time of the accident, the aircraft was traveling at an estimated speed of 115 knots. While weather conditions were generally suitable, increasing wind speeds in the mountainous terrain had created patches of moderate turbulence, which likely contributed to the incident.
The investigation
Investigators examined the mechanical and environmental factors surrounding the crash, focusing on the aircraft's vulnerability to low-G conditions. The inquiry established that the helicopter's light gross weight and high airspeed likely intensified the impact of turbulence. The investigation also looked into the global safety record of the Robinson R66, noting that several similar accidents had occurred worldwide since the model's 2010 introduction. Furthermore, the Commission reviewed the certification and training standards provided by the Federal Aviation Administration (FAA) and the Civil Aviation Authority of New Zealand, specifically regarding the lack of specialized training requirements for this specific model compared to its predecessors.
Findings
- The primary cause of the in-flight breakup was a mast bump and subsequent contact between the main rotor blade and the fuselage.
- The occurrence of the mast bump was likely triggered by moderate or greater turbulence, which induced a low-G state.
- The Robinson R66 shares the same main rotor system design as the R22 and R44, making it susceptible to similar catastrophic failures under specific conditions.
- At the time of the accident, flight manuals did not provide sufficient warnings regarding the environmental conditions and operating practices that could lead to a mast bump.
- There was a significant lack of specialized training requirements for the R66, which meant pilots could operate the aircraft without the specific knowledge necessary to mitigate these risks.
Safety action
Following the investigation, recommendations were directed toward the FAA and the Director of Civil Aviation to implement mandatory additional training as a prerequisite for R66 type ratings. There was also a call to reinstate research into the dynamic behavior of lightweight, two-bladed, teetering rotor systems to better understand the mechanics of mast bumps. Additionally, authorities were advised to publicize updated manufacturer handbooks that caution against flying in high winds and turbulence.