WPR16LA132

The helicopter pilot was performing an agricultural flight when he felt an airframe vibration, which was followed by the main rotor low rpm warning and a loss of rotor rpm. He reduced collective and the vibration and warning horn stopped. As he began to maneuver for a landing, he increased the collective and leveled the skids and again felt an airframe vibration and noted a loss of rotor rpm. During the landing on sloping terrain, the right front skid toe dug into the soft dirt and the helicopter came to rest on its side, resulting in substantial damage. Examination of the helicopter revealed no mechanical anomalies that would have precluded normal operation, and the reason for the vibration and loss of rotor rpm could not be determined based on the available information.

On June 27, 2016, at 2010 Pacific daylight time, a Robinson R44 helicopter, N8325X, was substantially damaged when it was involved in an accident near El Centro, California. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 137 agricultural flight. The pilot reported that, during the preflight inspection, the main fuel tank was about half full and the auxiliary fuel tank was 1/4 full. He completed the preflight inspection and performed an engine start and run up; both were normal. After departure, the pilot climbed the helicopter to 400 ft above ground level (agl) and flew toward the field. While in cruise flight, the pilot felt a vibration in the airframe followed immediately by the low rotor rpm warning. He noted that the rotor rpm was decreasing, which he arrested by reducing collective. At that point, the airframe vibration had either stopped or subsided, and the low rotor rpm warning stopped. The pilot entered a shallow right turn and located a dirt road as a forced landing site. As he approached at 50 ft agl, he began to flare and increased engine power; the engine rpm increased to the green arc and matched the rotor rpm. As he increased the collective and leveled the skids, he again felt the airframe vibration and the rotor rpm decreased. As the helicopter neared the ground, the pilot saw that the dirt road was down sloping. He turned toward the right and landed. During the ground slide, the right front skid toe dug into the soft dirt and the helicopter pitched forward and to the right. The main rotor blades contacted the ground, and the helicopter came to rest on its right side. Federal Aviation Administration (FAA) inspectors examined the helicopter and noted that the main rotor blades were coned upward with chordwise creases from the hub to the tip. The right-side skid toe had broken off just forward of the forward attachment point. The tail boom was buckled just aft of the fuselage attachment point. The tail rotor blades, and tail skid were undamaged. The horizontal stabilizer exhibited crush deformation. The collective was in the full-up position and the pedals were stuck in the full-left position. The FAA inspectors did not free the collective or pedals to perform the flight control continuity check. All four V-belts remained intact, with the three forward V-belts displaced forward off their tracks. The alternator belt remained intact. The left main fuel tank contained about 6 inches of fuel and the right auxiliary fuel tank contained about 2 inches of fuel. Samples of the fuel revealed no debris and coloration consistent with 100 low-lead aviation fuel.