Accident Details
On June 6, 2022, at approximately 0950 central daylight time, a Robinson R44 helicopter, registration N94WC, was substantially damaged when it rolled onto its left side during a personal flight near Henderson, Texas. The pilot sustained serious injuries, and the passenger sustained minor injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91.
According to the passenger, the pilot was practicing hover takeoffs and landings in a crosswind. While hovering before a landing, the helicopter shuddered, and the left skid contacted the ground, causing the helicopter to roll over. The main rotor blades and tail boom sustained substantial damage.
Examination Findings
Examination of the helicopter's flight control systems and main and tail rotor drive systems revealed no preimpact anomalies. During the engine examination, the valve covers and bottom spark plugs were removed. The crankshaft was rotated by hand, and thumb compression was obtained at all cylinders except the No. 2 cylinder. Further inspection of the No. 2 cylinder showed that the exhaust push rod was bent and the exhaust valve was stuck. Borescope inspection revealed that the exhaust valve had contacted the piston, and the intake valve appeared recessed in the No. 2 valve seat.
Service Bulletin History
A review of the engine logbooks showed no indication of compliance with Lycoming Engines Mandatory Service Bulletin 388C, titled "Procedure to Determine Exhaust Valve and Guide Condition." The service bulletin recommended compliance every 300 hours or if valve sticking was suspected. It cautioned that failure to comply could result in engine failure due to excessive carbon buildup between the valve guide and valve stem, leading to sticking valves or broken exhaust valves.
Manufacturer Observations
According to Robinson Helicopter Company, past experiences with a stuck valve in an R44 have resulted in pilots reporting symptoms such as vibrations felt through the airframe, popping or misfiring from the exhaust, loss of power, low rotor RPM, and/or engine RPM fluctuations.