Flight Details
On April 30, 2018, at about 1330 Pacific daylight time, a Robinson Helicopter Company R44 II, registration N423ML, was substantially damaged during an accident near Borrego Springs, California. One passenger received minor injuries; the pilot and two passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 business flight.
The helicopter departed earlier in the day from Palm Springs International Airport (PSP), Palm Springs, California, to drop off passengers at a golf club in Borrego Springs. The flight was uneventful. At 1230, the pilot received a telephone call indicating the passengers were ready for pickup. The pilot inquired about wind conditions at the golf course and was told the wind was between 4 and 5 knots.
Emergency Sequence
During the flight to pick up the passengers, the pilot reported experiencing strong winds while traveling over mountainous terrain. The pilot landed at the golf course and performed a shutdown. Before takeoff, the pilot noted the wind direction and an increase in wind velocity. The helicopter departed toward the east and then turned northwest, maintaining an airspeed of 70 knots and climbing to 2,500 ft above ground level.
About 10 minutes later, the pilot heard a light thump accompanied by a small yaw from left to right, initially thought to be wind induced. Shortly thereafter, the clutch light illuminated, and the pilot began a 10-second countdown per the pilot's operating handbook. Five seconds into the countdown, the low rotor rpm warning light illuminated and the low rotor warning horn annunciated.
The pilot lowered the collective fully and applied aft cyclic to maintain rotor rpm and 70 knots airspeed, then rolled off the throttle and entered autorotation. The low rotor rpm horn and light continued, but the clutch light extinguished. Rotor rpm increased to 100%, and the warnings ceased. The pilot selected a forced landing site free of obstacles but with uneven, sandy terrain, maneuvering to land into the wind.
Landing and Damage
While descending at 50 ft agl, the wind switched from a headwind to a tailwind, causing the low rotor rpm light and horn to annunciate again. Unable to maneuver back into the wind due to low altitude, the pilot rolled on the throttle and applied a cyclic flare to reduce descent rate and airspeed. At 10 ft agl, the pilot began leveling the helicopter. As it settled through 5 ft agl, the helicopter weathervaned, bringing the nose left. The pilot used full collective just before touchdown. The helicopter landed on both skids before rolling onto its right side.
Photographs showed the landing gear remained attached but spread outward. The main rotor blades were in the debris adjacent to the main rotor mast. The tail section, tail rotor assembly, stabilizers, and tail rotor guard came to rest forward of the main wreckage.
Wreckage Examination
Postaccident examination of the drive system revealed the belt tension actuator was undamaged and extended about 1.3 inches. Upper and lower support bearings rotated smoothly. The upper sheave rotated smoothly clockwise but locked counterclockwise. The forward flex coupling was secure. The main rotor gearbox was undamaged, with dark blue oil visible. The mast and driveshaft were straight; the main rotor rotated 360° with no anomalies.
One main rotor blade was bowed downward near the root and bent downward and aft near the tip, with spar bent upward 90° and separated skins. The other blade was bent downward near the root and partially separated, with multiple dents and creases. The tail rotor driveshaft was bent and disconnected forward of the damper bearing. The tail rotor gearbox was partially separated; both tail rotor blades sustained impact damage, with one missing 6 inches of tip and the other missing half its tip cap.
No mechanical malfunctions or anomalies were found that would have precluded normal operation.