Henderson, TX, USA
N94WC
ROBINSON HELICOPTER R44
The helicopter pilot was practicing hover takeoffs and landings in a crosswind. The passenger reported that, while hovering before a landing, the helicopter shuddered, and the left skid contacted the ground. The helicopter rolled onto its left side. The helicopter sustained substantial damage to the main rotor blades, fuselage, and tail boom. Examination of the helicopter’s flight control systems and main and tail rotor drive systems did not show any preimpact anomalies that would have precluded normal operation. Examination of the No. 2 cylinder revealed that the exhaust push rod was bent and the exhaust valve was stuck. Borescope inspection of the No. 2 cylinder showed that the exhaust valve had contacted the piston and the intake valve appeared to be recessed in the No. 2 valve seat. The loss of engine power was most likely due to the stuck exhaust valve on the No. 2 cylinder.
On June 6, 2022, about 0950 central daylight time, a Robinson R44 helicopter, N94WC, was substantially damaged when it was involved in an accident near Henderson, Texas. The pilot sustained serious injuries and the passenger sustained minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The passenger reported that the pilot was practicing hover takeoffs and landings in a crosswind. She stated that, while hovering before a landing, the helicopter shuddered, and the left skid contacted the ground. The helicopter rolled onto its left side. The helicopter sustained substantial damage to the main rotor blades and tail boom. Examination of the helicopter’s flight control systems and main and tail rotor drive systems did not show any preimpact anomalies. During the engine examination the valve covers, and bottom sparkplugs were removed. The crankshaft was rotated by hand and thumb compression was obtained at all cylinders except the No. 2 cylinder. Examination of the No. 2 cylinder revealed that the exhaust push rod was bent and the exhaust valve was found stuck. Borescope inspection of the No. 2 cylinder showed that the exhaust valve had contacted the piston. The intake valve appeared to be recessed in the No. 2 valve seat. A review of the engine logbooks showed no indication of compliance with Lycoming Engines Mandatory Service Bulletin 388C, “Procedure to Determine Exhaust Valve and Guide Condition.” The service bulletin recommended compliance every 300 hours or if valve sticking is suspected and cautioned that “Failure to comply with the provisions of this publication could result in engine failure due to excessive carbon build up between the valve guide and valve stem resulting in sticking valves or broken exhaust valves...” According to Robinson, past experiences of a stuck valve in a R44 have resulted in the pilots reporting some or all the following symptoms: vibrations felt through the airframe, popping, or misfiring out of the exhaust, loss of power, low rotor RPM and/or engine RPM fluctuations.
The partial loss of engine power in a hover due to a stuck exhaust valve.
Source: NTSB Aviation Accident Database
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