Accident Overview
On 14 November 2016, a Robinson Helicopter Company R66 helicopter, registration ZK-HAG, was conducting agricultural spraying operations in the Hokonui Hills, Southland. The flight was the last spray run of the day, with one pilot on board. During a descending turn, the low rotor revolutions-per-minute (RPM) warning light and horn activated. The pilot responded by lowering the collective lever, and rotor RPM recovered. However, when the helicopter leveled out, the warnings activated again. At that point, the helicopter lacked sufficient height or airspeed to recover, so the pilot turned toward a more suitable area and attempted a run-on landing.
Sequence of Events
The helicopter struck the ground heavily at a shallow angle, bounced, and pitched forward, causing the main rotor blades to contact the ground. The helicopter rolled onto its left side and rotated 360 degrees as the blades dug into the ground. The tail section separated, and the main rotor blades broke off approximately 600 millimeters from the center of the main rotor head. The engine continued running until the pilot shut it down by closing the fuel cut-off valve. The pilot then turned off the master electrics and emergency locator transmitter, climbed out, and canceled the ELT alert by phone. The pilot sustained minor bruising; there was no post-accident fire.
Aircraft and Personnel
The Robinson R66 is a light helicopter powered by a single Rolls-Royce RR300 turbine engine. It had been imported into New Zealand in February 2011 and purchased by the operator in September 2014. Total airframe and engine time was 1,683.9 hours. The helicopter was equipped with an agricultural spray system approved under Civil Aviation Rules Part 137. The operator held a Part 137 operating certificate for commercial agricultural operations and operated four helicopters at the time. The pilot had a commercial pilot license (helicopter) since October 2004, with 4,400 total flight hours, including 660 hours on the R66 and 3,020 hours on agricultural operations. The pilot was the operator's chief pilot. All licensing and medical requirements were current.
Cause and Safety Issues
According to the Transport Accident Investigation Commission (Commission), the low rotor RPM condition very likely resulted from a momentary reduction in available engine power caused by contaminated fuel. The Commission also found that the operator’s refueling procedures for remote sites left several opportunities for fuel contamination to occur. The Commission identified a safety issue: more educational material is needed to alert operators to the risk of contaminated fuel when operating and refueling in remote, dusty environments. The Commission made two recommendations: one to the Director of Civil Aviation to provide more educational material and guidance on mitigating the risk, and another to the President of Aviation New Zealand to promulgate lessons learned to its members.
The key lessons from the inquiry include: refueling aircraft at remote locations increases the risk of fuel contamination, and aircraft fuel-filtering systems are an important defense. Operators should consider fitting additional airframe filters when operating at remote locations.