ROBINSON HELICOPTER COMPANY R44 II

Full Narrative

On September 15, 2024, about 1715 mountain daylight time, a Robinson Helicopter Company R44 II helicopter, N233WT, was substantially damaged when it was involved in an accident near Basin, Montana. The pilot and two passengers were seriously injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
The helicopter pilot reported that he was departing from an off-airport landing zone at an elevation of 7,120 ft mean sea level (msl), which was surrounded by towering trees in mountainous terrain. His performance calculation indicated that the helicopter would be able to hover and take off at an altitude up to about 7,700 ft msl. Shortly after an uneventful startup and magneto check, the pilot slightly raised the collective lever and determined that the wind was coming from the north, which aligned with the pilot’s decision to depart to the north.
After takeoff, as the helicopter reached the tree line, the pilot reported that he encountered mechanical turbulence and that the helicopter started to lose engine and rotor rpm. Subsequently, the helicopter started to settle and descend toward the ground. The pilot maneuvered and attempted to land the helicopter in a small clearing in a wooded area, but the helicopter continued its descent, struck trees, and impacted terrain. The helicopter sustained substantial damage to its fuselage and drive train.
Data retrieved from a cockpit video recorder revealed that during the start-up sequence, from about 1708 to 1710, the pilot programed the GPS and corrected the altimeter setting to read 7,150 ft. About 1711, the pilot increased the engine and rotor rpm settings to 100% and lifted the helicopter to a hover, maneuvering the helicopter over a body of water. Shortly after, the full throttle light illuminated. (According to the manufacturer, this light indicates that the engine is near full throttle and that the governor will be ineffective because it cannot increase the throttle setting to maintain rpm.) The pilot then raised the collective, but the helicopter stopped its climb and settled to the ground while the pilot maintained the collective lever position. The pilot commented to the passengers that they could not depart from their current location. As the pilot lowered the helicopter to the ground, while in ground effect, the full throttle light extinguished. The pilot then increased the collective lever position and the full throttle light illuminated again. The helicopter stopped climbing, and the pilot once again landed the helicopter.
After the pilot and the passengers discussed other options to leave the mountain site, the pilot stated that “cooler temperatures or better wind is key” and that he could take off and “fly in a little circle,” but it was “not super recommended.” A passenger replied that there was not much room for a “circle” takeoff, and the pilot acknowledged that he knew that to be the case. Shortly after, the pilot commented, “let me just play around here for a second” and then slowly lifted the helicopter into a low hover, after which the full throttle light illuminated. The helicopter yawed slightly to the right and began to climb. At 1714:07, as the helicopter continued a slow climbing right turn, the engine and rotor rpms reduced to 95%, a warning horn sounded, and a warning light illuminated on the annunciator panel. (According to the manufacturer, the low rotor light and horn indicate that the rotor speed is below 97%. To restore the rotor speed, the pilot should immediately lower the collective lever, roll the throttle on, and, while in forward flight, apply aft cyclic; the light is disabled when the collective is in the full down position.) These light and horn warnings continued throughout the rest of the flight.
The cockpit video recorder showed that the engine and rotor rpms reduced to about 90% at 1714:09. The helicopter then shallowed its right turn after the helicopter turned 270° from its original departure heading. At 1714:12, the rpms reduced to about 85%. At 1714:16, the altimeter reached a maximum indicated altitude of 7,220 ft, and the right turn rate began to increase. The helicopter began rolling right, and it impacted terrain at 1714:34, at which time the engine and rotor rpms indicated about 60%. The recording ended at 1715:40.
The pilot initially reported that there were no mechanical failures or malfunctions with the helicopter that would have precluded normal operation. In March 2025, the pilot added that there could have been something wrong with the fuel he received at his last departure point of Townsend Airport (8U8), Townsend, Montana. No information was provided by the airport manager after multiple attempts by the investigation to obtain fuel quality check records from around the time of the accident, and the helicopter wreckage was no longer available for examination of the engine or fuel system at the time the pilot reported his fuel concerns. The pilot did not report whether he took a preflight fuel sample before the accident takeoff.
Based on the weight and balance data provided by the pilot, the helicopter was within the center of gravity envelope as recommended by the manufacturer. The pilot reported that the total weight of the helicopter at the time of departure was 2,182 lbs, which consisted of the helicopter’s empty weight of 1,602 lbs, a fuel weight of 90 lbs, and a crew and passenger weight of 490 lbs. The manufacturer’s recommended maximum takeoff weight was 2,500 lbs. The pilot reported that the temperature during his departure was about 60°F; based on the manufacturer’s density altitude chart, the density altitude was about 8,500 ft.
According to the manufacturer’s in-ground effect performance chart (at 2-ft skid height, full throttle, and zero wind), with the helicopter at 2,182 lbs and the temperature at 60°F, the helicopter could operate in ground effect up to a pressure altitude of about 10,000 ft.
According to the manufacturer’s out-of-ground effect performance chart (takeoff power or full throttle and zero wind), with the helicopter at 2,182 lbs and the temperature at 60°F, the helicopter could operate out of ground effect up to a pressure altitude of about 7,000 ft.
According to the manufacturer’s height–velocity diagram, with the helicopter departing from a hover and climbing up to 100 ft above ground level, the pilot was operating the helicopter within the “avoid operation in” shaded area.