Robinson R44 N616HS accident near Williamsburg, Virginia

Probable cause

The pilot's failure to safely operate the helicopter due to his impaired cognitive and physical abilities, which resulted in a loss of control.

NTSB analysis

On the morning of the accident, the pilot flew the helicopter cross-country to attend a meeting at another airport. He departed on the return flight to his home airport later that afternoon and climbed the helicopter to an altitude of about 1,700 ft, leveled off, and the groundspeed increased. About 3 minutes after takeoff, the helicopter entered a right descending turn that continued until it impacted a condominium building at a high vertical speed. Witnesses reported that the helicopter rocked "back and forth unsteadily" before it suddenly pitched downward to impact the roof of the building.

Examination of the wreckage revealed no anomalies that would have precluded normal operation. The engine crankshaft gear bolt was found unthreaded and the alignment pin for the crankshaft gear was found sheared. The locking tab designed to prevent rotation of the bolt was found attached and intact. Examination of the bolt, locking tab, and accessory gears revealed no pre-impact damage. Had the bolt unthreaded during flight, the engine would have stopped running; however, the engine oil coolers exhibited grinding damage consistent with the engine rotating at the time of impact, and witnesses reported hearing the engine running continuously until the impact. It is therefore likely that the bolt unthreaded during the accident sequence. The forward-facing accessory case cover was found impact damaged and partially missing. Had the accessory gear train stopped rotating due to impact or from fragments of the cover or debris in the gear mesh, the crankshaft could continue to rotate briefly, allowing the bolt to unthread without damaging the locking tab.

The 85-year-old pilot was diagnosed with Parkinson's disease about 3 years before the accident. He experienced tremors in both hands, which was treated with medication and surgery with some success. The tremors consistently affected his left hand more than the right, and he reported that the tremors were more pronounced later in the day. Although the severity of his tremors or to what degree they may have affected his ability to fly the helicopter could not be determined, it is possible that they may have had more of an effect during the accident flight than on the day's earlier flight.

In the 2 years preceding the accident, the pilot's doctors noted mild dementia and mild cognitive impairment. His dementia was treated with medication (which he subsequently discontinued), and reportedly improved, although his mild cognitive impairment persisted. His doctors also noted that the pilot had impaired measures of simple attention and visual scanning and tracking speed, and mild, relative difficulty with sustained attention. They recommended that the pilot not fly due to concerns with his attention, reaction time, and judgment.

It is likely that impairment resulted from one or more of the pilot's well-documented progressive impaired cognitive and physical abilities negatively affected his ability to safely operate the helicopter and led to the loss of control.

Text from the NTSB. Open the NTSB docket for ERA18FA187 for the full record.