ERA20FA074

A severe left roll excursion after the onset of pitch and roll oscillations, which were not arrested by the pilot for undetermined reasons. This resulted in main rotor blade contact with the airframe and a subsequent inflight breakup of the helicopter.

The helicopter pilot was conducting a night cross-country flight in visual meteorological conditions. Recorded data showed that while the helicopter was flying at an altitude of about 2,300 ft mean sea level and at an indicated airspeed of about 107 knots, slight pitch and roll oscillations occurred for about 20 seconds followed by a left roll that continued until the helicopter was inverted. A main rotor blade contacted the tailboom, leading to an in-flight breakup over a residential area. Postaccident examination of the airframe, flight controls, and engine assembly revealed no evidence of a preimpact failure or malfunction. Because the helicopter’s pitch and roll values changed only minimally before the in-flight upset, the autopilot was likely engaged when the pitch and roll oscillations started. The pitch and roll oscillations might have been the result of the autopilot reacting to an external disturbance, specifically, the moderatetosevere turbulence that was reported in the area. Another possible cause of the pitch and roll oscillations was the pilot manually manipulating the cyclic control. Additionally, an in-flight malfunction of the autopilot’s roll servo actuator could not be ruled out as the source for the pitch and roll oscillations. While any of these scenarios might have precipitated the initial oscillations, none would have precluded the pilot from overriding the autopilot and manually flying the helicopter. Even though the helicopter was equipped with devices that recorded flight and engine data at a rate of at least one parameter every second, the lack of an on-board crash-resistant cockpit imaging system precluded a determination of the pilot’s actions, or lack of actions, in response to the pitch and roll oscillations. About 6 months after this accident, the National Transportation Safety Board issued a safety recommendation requesting that major helicopter manufacturers, including the manufacturer of the accident helicopter, install crash-resistant flight recorders with cockpit imaging systems for existing helicopters. The helicopter manufacturer responded that it incorporated a cockpit camera system as standard equipment on all similar model helicopters manufactured beginning the year after the accident and offered as a kit for existing helicopters the same year. The cameras were not designed to be crash-resistant.   The pilot was not likely impaired or incapacitated by his diagnosed obstructive sleep apnea given the information about his effective continuous positive airway pressure device use. Also, some or all the ethanol detected in the pilot’s specimens might have been from a source other than ingestion. The possibility of an impairing or incapacitating medical event or impairing effects from the pilot’s use of clonazepam (alone or in combination with ethanol effects) could not be determined from the available evidence. However, no operational evidence indicated that the pilot’s performance was deficient during the flight time preceding the oscillations.

An autopsy of the pilot was performed by Forensic Pathology, Cumberland County Coroner's Office During 2001 and 2009, the pilot was diagnosed with obstructive sleep apnea and coronary artery disease, respectively. According to documentation provided to the FAA, cardiac catheterization had shown mild-to-moderate triple-vessel coronary artery disease that did not require stenting or surgery, and the pilot did not have any typical symptoms of related heart pain or congestive heart failure. Medical records from the pilot’s most recent visit to his primary care provider on November 27, 2019, showed that the pilot was using a continuous positive airway pressure (CPAP) device to treat his sleep apnea with good adherence and symptom control. The records also showed that the pilot was not adhering to treatment for high blood pressure but that he had no cardiovascular symptoms and a blood pressure of that was slightly higher than his goal. During the year preceding the accident, the pilot used his CPAP 85% of the time with an average use of 8 hours 6 minutes. During the 7 days preceding the accident, the pilot used his CPAP every night with an average use of 7 hours 38 minutes per night and 8 hours 6 minutes of use on the night before the accident. According to records provided by Robinson Helicopter Company, the pilot attended a safety course in February 2019 for the R66. At that time, the pilot had not accumulated any hours in the R66. On the evaluation document, the instructor indicated that the pilot had “very good control” of the helicopter when performing normal and emergency procedures and that he was “very comfortable practicing the [autorotations].” The instructor suggested that the pilot obtain more training on emergency procedures. The pilot was rated “average” on all demonstrated maneuvers. The helicopter was manufactured in January 2019 and was purchased shortly afterward by a company associated with the pilot. At the time of the accident, the hour meter indicated about 167 hours. The helicopter was equipped with a semirigid rotor system that rotated counterclockwise (when viewed from above). According to Robinson Safety Notice (SN) 11, Low-G Pushovers – Extremely Dangerous, pushing the cyclic forward following a pull-up or rapid climb, or even from level flight produces a low-G (weightless) flight condition. The notice goes on to state that if forward cyclic is applied, the main rotor torque reaction will then combine with tail rotor thrust to produce a powerful right rolling momement of the fuselage. The helicopter was equipped with a Genesys Aerosystems HeliSAS two-axis autopilot system comprised of a flight control computer, HeliSAS control panel, and two servo-actuators (one each for the pitch and roll axes). The autopilot system was designed to record faults in the system. The downloaded data were unrecognizable by the manufacturer; therefore, no accident-related data were available from the HeliSAS. According to the R66 Pilot’s Operating Handbook Supplement for the HeliSAS, The primary autopilot mode is stability augmentation system (SAS) mode which maintains a steady helicopter attitude by applying corrective inputs to the cyclic. The autopilot does not provide any collective or pedal inputs. Additional modes providing heading hold, altitude hold, and navigation functionality are also selectable. The SAS mode of the autopilot was engaged by pressing either the SAS button on the control panel or the trim button mounted on the cyclic for more than 1.25 seconds. With the SAS mode engaged, the pilot can “fly through” the SAS to achieve a desired attitude and can subsequently press and release the trim button to reset the baseline attitude for the system to the current attitude. Pushing the SAS button on the control panel or the “AP [autopilot] OFF” button on the cyclic disengages the SAS mode (for manual control), and four aural beeps would sound in the pilot’s headset. Additionally, the HeliSAS is designed to automatically disengage when one of several predefined faults or malfunctions is detected, which would also produce four aural beeps in the pilot’s headset. Disengagement of an autopilot mode, such as heading or navigation, not commanded by the pilot (caused by, for example, the loss of a valid navigation signal) would be accompanied by a single beep in the pilot’s headset. Any intentional disengagement of an autopilot mode other than SAS would not trigger a beep sound in the pilot’s headset (because SAS mode would remain engaged). The helicopter crashed in a residential area that was located about 61 miles north-northwest of MTN. The main wreckage area, consisting of the fuselage, was located in the backyard of a residence. The fuselage was nearly inverted and was resting on its right side along a magnetic heading of 334°. The fuselage structure was not damaged, but the windshield bow had extensive impact damage. The bow retained its shape but was fractured at the roofline, and the windshield had fractured. Sections of windshield pieces remained attached to the bow. A portion of the tailboom was located about 30 to 40 ft above ground level in a tree next to the fuselage resting location. A ground scar about 10 inches deep was located about 30 ft from the nose resting position. Wreckage consisting of a section of a main rotor blade, the main rotor mast with attached sections of a main rotor blade, the tail rotor, the tail rotor control tubes, airframe structural tubes, and plexiglass were found away from the main wreckage, with the farthest located about 700 ft away. No evidence of pre- or postimpact fire was found on any portion of the wreckage. No bird remains or feathers were found in the main wreckage consisting of the fuselage, or in locations of the separated main rotor mast and tail rotor gearbox. A main rotor blade section that was about 5 ft long was located on the ground near the trunk of a small tree in the front yard of a residence; the blade section was located about 700 ft and 161° from the main wreckage. The leading edge of the blade was embedded into the ground, and the trailing edge of the blade was curved and exhibited red and black paint transfer on the upper surface near the fracture surface. Several feathers were found on the ground adjacent to the blade and near the tree, and several feathers were found adhered to the blade. The feathers and swabs of debris that had adhered to the separated portion of the main rotor blade were analyzed by the Smithsonian Institution’s Feather Identification Lab. The feathers were matched to museum specimens of a mourning dove, and the swabs of debris did not contain bird remains. Examination of the tail rotor drive, tail rotor flight controls, and main rotor flight controls revealed no evidence of preimpact failure or malfunction. Examination of the tailboom, which consisted of 7 bays, revealed damage to several of the bays. A horizontal dent was noted on the left side to the lower surface of bays 5, 6, and 7; the dent was consistent with contact with the leading edge of the blue main rotor blade. The rivet spacing of the tailboom in that area matched the indentations made in the blue main rotor blade. The tailboom was fractured at the aft bulkhead (bay 7). Yellow paint transfer was noted between bays 6 and 7 on the bottom. Slight paint transfer was noted on the left side of bay 4. An impact area (which had partially ruptured and was flattened) was noted on the left and lower side of bay 3. Bays 2 and 3 exhibited red, black, and yellow paint transfer on the left side. Examination of the engine revealed that all engine mounts were fractured in a manner consistent with overload. The engine-to-transmission shaft was fractured on both ends, and the shaft tube was found within the wreckage. This shaft’s forward flange remained attached to the forward flex plate and main gearbox input yoke, and its aft fl