CEN19LA121

Shortly after takeoff and while climbing through 200 to 250 ft above ground level in a left turn, the pilots of the helicopter noted an audible horn, low main rotor rpm, and a loss of altitude” indicating a loss of rotor RPM and engine power." The flying pilot entered an autorotation to recover rotor rpm, and the pilots located a forced landing location. Upon touchdown, the forward landing gear skids dug into the soft terrain, and the helicopter rocked forward and backward, resulting in the main rotor contacting the tail boom. An examination of the helicopter revealed no preimpact mechanical anomalies that would have precluded normal operation. The engine was removed and placed in a production test cell for an engine test run. The engine responded normally to all power demands without surging or hesitation. Based on the available evidence, the reason for the partial loss of engine power could not be determined.

On April 16, 2019, at 0730 central daylight time, a Bell OH-58A helicopter, N109PD, impacted terrain during an autorotation following a reported partial loss of engine power near Omaha, Nebraska. The pilot and co-pilot were not injured, and the helicopter sustained substantial damage to the tail boom. The helicopter was registered to and operated by the Omaha Police Department (OPD) as a public aircraft operations flight under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed in the area at the time of the accident. The flight originated from the North Omaha Airport (3N0), Omaha, Nebraska, at the time of the accident and was destined for Blair, Nebraska. According to the pilot, shortly after takeoff and climbing through 200 to 250 ft above ground level in a left turn, the pilots recognized an audible horn, low rotor RPM, and a loss of altitude "indicating a loss of rotor RPM and engine power." The pilot, who was seated in the right seat, entered an autorotation in an attempt to recover rotor RPM. The pilot and co-pilot observed the best suitable landing area was north and west of 3N0. Upon touchdown in the soft terrain, the forward landing gear skids dug into the terrain, and the helicopter rocked forward and backward which then caused the main rotor blades to contact the tail boom. The helicopter came to rest upright with the tail boom separated from the airframe. The pilots shut down the engine, which continued to operate about 35% N1, waited for the engine to stop, and exited the helicopter. A review of the maintenance records revealed that on March 15, 2019, the Rolls Royce T63-A-720 250-C20C engine shut off uncommanded during the cool down cycle. A 200-hour inspection was completed on March 16, 2019, at a total airframe time of 12,089.3 hours, which included the removal of fuel control and fuel pump, and replacement of the fuel filters. The fuel pump and fuel control were checked by a certified repair station and reinstalled onto the engine. No mechanical anomalies were noted during subsequent ground and flight tests. On March 21, 2019, the engine shut off uncommanded during the cool down cycle. The fuel control throttle rigging was checked, no obstructions were found in the intake/particle separator, and the helicopter was returned to service. At the time of the accident, the total airframe and engine times were 12,099.2 hours and 6,588 hours respectively. On April 23, 2019, the helicopter was examined by a Federal Aviation Administration (FAA) inspector, and representatives from the OPD and Rolls-Royce. No preimpact mechanical anomalies were noted during the examination with the airframe or engine. The engine was removed for further examination and testing. On July 16, 2019, the engine was examined at a Rolls-Royce's authorized maintenance center, Lafayette, Louisiana, under the supervision of the FAA. The engine was placed in a production test cell for an engine test run. The engine successfullycompleted ground idle, flight-idle, max-continuous-power, takeoff power runs, and "wave-off" maximum power increases. The engine responded normally to all power demands without surging or hesitation.