Robinson has added wire strike protection provisions to its R66 options list. Photo courtesy of Robinson Helicopter Co.
Robinson Helicopter Company is being sued by the families of pilots killed in June 2016 when their R66 broke up mid-flight over Arizona.
The suit, filed June 22 in Los Angeles County Superior Court, alleges defective manufacturing caused the in-flight breakup of the helicopter after a mast-bumping event and seeks damages for wrongful death, breach of warranties and negligence by the company.
According to the NTSB’s final accident report dated November 2017, the cause of the breakup and subsequent crash of the R66 was “an encounter with turbulence due to updrafts and/or dust devils that resulted in mast bumping and an in-flight break-up.”
Robinson President and Chairman Kurt Robinson told R&WI the company agrees with the NTSB findings, but that mast bumping is not a phenomenon unique to its helicopters.
“We have no reason to disagree with the NTSB,” Robinson said in a June 27 interview. The manufacturer conducts regular safety sessions around the world, he said.
The NTSB report also outlines witness narratives describing the windy weather conditions and “numerous large dust devils” near the accident site.
The lawsuit states the helicopter “was in straight and level cruise at approximately 90 knots,” and “suddenly broke up in flight and crashed.” The NTSB noted that there was "no recorded information available that could be used to determine the helicopter’s airspeed, altitude, or the pilot’s control inputs."
The lawsuit claims that mast bumping occurs more frequently in Robinson aircraft “due to the design of the rotor hub and main rotor blade assembly, the ability of the Robinson blades to independently pivot and teeth, combined with the inadequate mass of the main rotor blades, and resulting low rotor inertia, and their tendency to delaminate.”
It alleges the particular helicopter involved in the crash had a defective rotor system.
Mast bumping occurs when the rotor head contacts the rotor shaft in low-G conditions, which can occur in windy weather, according to the Aircraft Owners and Pilots Association’s web site. Two-blade or semi-rigid rotor systems, which the R66 features, are most susceptible to the phenomenon. Mast bumping can be avoided by exercising caution in turbulent air conditions and knowing how to maneuver the helicopter when encountering a low-g condition, according to AOPA.
Robinson in 2016 was put on New Zealand’s Transportation Accident Investigation Commission’s (TAIC) watchlist after the nation’s aviation authority investigated its 14th mast-bumping accident involving a Robinson since 1996. Media reports indicate 30% of New Zealand’s total helicopter fleet is Robinson aircraft.
A November 2016 safety alert issued by Robinson Helicopters outlines pilot operating procedures that would prevent mast bumping in such conditions.
“Remember, low-G pushovers are prohibited maneuvers in Robinson helicopters,” the safety alert cautions. “If low-G does occur, apply gentle aft cyclic as soon as you recognize it. Do not wait for a right roll to begin. Low-G-induced right roll indicates you are losing control of the helicopter.”
Mast bumping is not unique to Robinson aircraft. U.S. military Bell UH-1 Huey and AH-1z Cobras suffered a series of high-profile mast-bumping incidents in the 1970s and '80s.
Since 1979, Robinson Helicopters has delivered more than 12,000 civilian helicopters worldwide. Its factory at its Torrance, California, headquarters is capable of producing 1,000 helicopters annually.
Kurt Robinson told Heli-Expo attendees in March during a press briefing that more than 80% of its deliveries in 2017 occurred outside the U.S.
The law firm representing the plaintiffs in the lawsuit has represented more than 650 individuals in aviation accidents.