Accident Overview
On October 15, 2023, at approximately 0951 central daylight time, a Cirrus SR22 airplane, registered N6JA, sustained substantial damage during a landing accident at Red Oak Municipal Airport (RDK) in Red Oak, Iowa. The pilot and passenger were not injured. The airplane was being operated under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Flight History
ADS-B flight track data showed that the airplane departed Eppley Airfield (OMA) in Omaha, Nebraska, at 0920 and climbed to 7,000 feet mean sea level (msl) en route to St. Louis Downtown Airport (CPS) in St. Louis, Illinois. The pilot encountered icing conditions at 7,000 feet msl and requested a climb from air traffic control (ATC) to 9,000 feet msl. After climbing above the clouds into visual meteorological conditions, the engine began to run rough and engine power indications started to fluctuate.
Diversion and Landing
The pilot diverted to Red Oak Municipal Airport, a non-tower-controlled airport, and flew the RNAV (GPS) runway 5 approach. During the descent and arrival, the controller informed the pilot twice that runway 5 was closed. The pilot proceeded to land on runway 5, and the airplane impacted a barricade and ground equipment, resulting in substantial damage to the left wing.
Postaccident Examination
A postaccident examination of the engine and subsequent laboratory testing by the National Transportation Safety Board Materials Lab revealed that the No. 4 cylinder exhaust valve failed as a result of wear of the exhaust valve guide. The wear caused the valve to seat improperly, leading to valve head deformation, hard contact with the valve seat, and failure of the exhaust valve rotocoil. A portion of the valve face exited the No. 4 cylinder through the exhaust system and entered the left side turbocharger assembly. The exhaust turbine blades sustained damage along the leading edges before the valve face exited through the left side exhaust. The fractured valve face was not recovered.
Further examination showed the No. 4 exhaust valve head was fractured. The combustion face was covered with combustion products, with some regions exhibiting a red/purple tint. The fracture initiated in the fillet on the downstream-facing side of the valve head and progressed through to the combustion face. The origin sustained some post-fracture impact damage, but no pre-existing anomalies were apparent. The valve head's seat face was worn, and the valve head was dished/mushroomed; the valve stem displayed a buildup of combustion products below the region that engaged the valve guide.
The No. 4 exhaust rotocoil was worn, and the race was covered in cooked oil except for a 0.080-inch-wide annular track contacted by the spring. The spring was worn flat on the side contacting the washer.
Borescope examinations of the remaining cylinders indicated that the No. 6 cylinder exhaust valve face showed uneven heat damage consistent with a failing valve.
Maintenance Records
Review of the airframe and engine maintenance records showed that the airplane's most recent annual inspection was completed on September 25, 2022.
Runway Information
Red Oak Municipal Airport was equipped with three runways: runway 5/23, 5,100 ft long by 75 ft wide; runway 17/35, 2,901 ft by 60 ft; and runway 13/31, grass, measuring 2,050 ft by 210 ft. GPS instrument approach procedures were available for runways 5 and 17.