Robinson R44 accident near Hayward, California, July 15, 2019

The NTSB's narrative final · quoted from the NTSB record

Following several rounds in the helicopter airport traffic pattern, the flight instructor and student pilot performed hovering maneuvers on a taxiway designated for helicopter training. During one of the hovering maneuvers, the helicopter drifted away from the taxiway, over the grass area, and rapidly advanced towards a fence line. According to the student pilot, the flight instructor initiated a left turn, and the helicopter turned “very rapidly.” Analysis of a surveillance video indicated the helicopter rolled left about 70° as it neared the fence line. The helicopter’s bank angle decreased to about 40° as the helicopter continued to turn left. As the helicopter turned to a northern heading, the left roll angle increased to about 90°. The main rotor blades contacted the ground immediately after and the helicopter came to rest. Postaccident examination of the helicopter revealed a punch tool at the aft bulkhead of the cabin resting against the tail rotor control bell crank. Testing performed by the helicopter manufacturer indicated the proximity of the punch to the tail rotor control bell crank could have inhibited some tail rotor control authority. However, as the examination did not reveal any other anomalies with the flight control system or powerplant, even if the pilot’s tail rotor authority was inhibited, he still had the authority to reduce engine power, lower the collective and land the helicopter at any moment during the flight. Further, the restricted tail rotor authority would not have affected the helicopter’s roll axis, and the rapid, steep roll angles that occurred moments before impact. The instructor and student pilot likely lost control of the helicopter during its final 90° left bank, but the cause of this and previous excessive bank angles and whether they were intended during the helicopter’s final movements could not be determined. The student pilot’s history with another flight instructor, of aggressive control inputs and lack of attention to the surrounding environment suggest that the instructor, in the accident, may have been forced to intervene and recover the helicopter. However, a lack of available evidence precluded the investigation from determining when this intervention occurred and whether it contributed to the accident.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.