A Robinson helicopter accident on June 29, 1992, involving the inflight break-up of the helicopter prompted the National Transportation Safety Board (NTSB) to launch a special investigation into Robinson R22 and R44 helicopter main rotor control accidents. The Federal Aviation Administration (FAA) was already aware of potential design flaws of the helicopter causing inflight break-ups and fatal accidents. The FAA had conducted two special certification reviews and initiated a third. The FAA also hosted a technical panel regarding main rotor control accidents and commissioned the Georgia Institute of Technology to conduct simulation studies of the helicopter’s main rotor system and its potential to contact the helicopter’s airframe.
As a result, in 1995, the FAA took the unusual step by issuing Special Federal Aviation Regulation (SFAR) 73), requiring special helicopter training and proficiency requirements, but for only Robinson R22 and R44 helicopters. The next year, in 1996, the NTSB issued special investigation report focusing on the issue of recognizing and preventing the phenomena of “mast-bumping.”
“Mast-bumping” is a known problem in helicopters which have only two main rotor blades. In a two-bladed helicopter like the R22 or R44, if one blade flaps up the other blade flaps down. Due to the design of two bladed rotors, as the aft rotor blade root flaps down it will travel closer to the mast. If the flapping is excessive, it may contact the rotor mast and cause damage. Mast-bumping is a dangerous condition that can become catastrophic in flight. If the flapping of the rotor blades become severe enough, the rotor blade can strike and sever the tailboom off, or strike the fuselage, or damage the mast, all potentially to the point that the entire rotor system becomes inoperable and a crash is inevitable.
The NTSB’s special investigation focused in part on low G maneuvers, rotor blade stall, large and abrupt control inputs and turbulence that could cause mast-bumping. The NTSB then concluded that in the case of R22 and R44 helicopters, “the low inertia main rotor blade can diverge from normal rotation to strike the body of the helicopter in just a few revolutions of the blade.” The NTSB further surmised:
[B]ecause of the high responsiveness of the R22 to cyclic input and the rapidness with which the rotor blade could diverge and strike the fuselage, it is possible that diversion of attention… could result in a control input and subsequent change in aircraft attitude that requires corrective action to which even an experienced pilot may inadvertently respond with large, abrupt movement of the cyclic control.
The NTSB stated that while the SFAR 73 and FAA’s other operational changes may not eliminate all in-flight rotor strikes, that “absence of such accidents since these actions were implemented suggests that they have been effective.”
The NTSB and FAA basically concluded their investigation in 1996 by laying causation of these R22 and R44 accidents on the pilots and their handling of the helicopter.
ALG does not agree with the NTSB’s conclusion that it is simply pilot error that is causing the main rotor to impact the aircraft. While it is true that since SFAR 73 was introduced loss of main rotor control accidents have occurred less frequently, they still occur far too often.
Based on ALG’s investigation, since 2000, in the United States alone, there have been 14 fatal accidents attributed to mast-bumping and resulting rotor-fuselage strike and loss of helicopter control. These accidents have resulted in 26 deaths. These accident statistics, however, do not include the five fatalities in the two most recent R44 accidents in Washington State and Hawaii, in which both helicopters showed signs of tailboom separation prior to the loss of aircraft control.
New Zealand Adds the R44 & R22 to Safety Watchlist
ALG is not alone in suspecting a major design flaw in the Robinson helicopter design. New Zealand’s Transportation Accident Investigation Commission (TAIC) has investigated a large number of similar accidents since 1996. As of July 2017, TIAC recorded 14 low-G mast bumping accidents in the R22, R44, and R66 with all but two of the accidents resulting in fatalities. TIAC’s investigations found that, while these types of accidents can be caused by sudden turbulence or abrupt flight-control inputs, based upon direct evidence and eyewitness testimony, in most cases pilot handling was not the cause of the main rotor departing its normal plane of rotation, and that their investigators are unable to explain the cause of these accidents. TIAC’s probable cause determination for these accidents are basically the same: “the divergence of the main rotor from its normal plane of rotation for an undetermined reason.”
In response to these accident investigations in 2018, the New Zealand Department of Conservation (DOC) ceased flying all Robinson helicopter models. The department concluded:
“Ensuring employee safety in Robinson helicopters relies heavily on pilots flying within strict operating limits at all times. We are not confident that we can rely on this consistently over time across many varied conditions that DOC employees face when in helicopters.”
Robinson Helicopter’s response is essentially that when flown within the normal flight envelope, their helicopters are safe. The problem is, and which was clearly expressed by New Zealand’s DOC, that the safe flight envelope may be too narrow. In the real-world helicopters operate in a dynamic environment in which they can routinely and unpredictably encounter weather and/or flight conditions that can easily exceed Robinson’s narrow envelope for safe flight.
In our opinion, there is something inherently wrong in the design when a helicopter’s main rotor is allowed to impact the fuselage or the tailboom, even when operating in unexpected flight conditions such as gusty winds or moderate turbulence. Those conditions may be unpredictable and not forecast before or during flight. Based on the continued occurrence of mast-bumping accidents resulting in rotor impact to the helicopter, ALG is strongly encouraging both the NTSB and the FAA to reopen their investigations into the continued tragic loss of life as reflected in the recurring Robinson helicopter self-rotor strike accidents.
ALG attorneys have handled many helicopter accident cases including similar Robinson Helicopter cases involving self-rotor strikes. ALG attorneys take cases in all 50 states and Canada, and are licensed in Hawaii, Washington, California, Alaska and Florida. If a loved one or friend has been involved in an aviation accident, we invite you to contact our office for a free consultation.