CEN24LA011

Factual narrative

On October 15, 2023, about 0951 central daylight time, a Cirrus SR22 airplane, N6JA, was substantially damaged when it was involved in an accident at Red Oak Municipal Airport (RDK), Red Oak, Iowa. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. ADS-B flight track information revealed that the airplane departed Eppley Airfield (OMA), Omaha, Nebraska, at 0920 and climbed to 7,000 ft mean sea level (msl) enroute to St Louis Downtown Airport (CPS), St Louis, Illinois. The pilot encountered icing conditions at 7,000 ft msl and requested a climb from air traffic control (ATC) to 9,000 ft msl. After climbing above the clouds into visual meteorological conditions, the engine began to run rough and engine power indications began to fluctuate. The pilot diverted to RDK, a non-tower-controlled airport, and flew the RNAV (GPS) runway 5 approach. During the descent and arrival to RDK, 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, which resulted in substantial damage to the left wing. 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 of the valve guide caused the valve to seat improperly, which led to valve head deformation, hard contact of the valve head 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 received damage along the leading blade edges before the valve face exited through the left side exhaust. The fractured valve face was not recovered. The No. 4 exhaust valve head was fractured. The combustion face was covered with combustion products and some regions exhibited a red/purple tint. The fracture initiated in the fillet on the downstream-facing side of the valve head and progressed through the head to the combustion face. The origin sustained some post-fracture impact damage, but there were no apparent pre-existing anomalies at the crack origin. The valve head’s seat face was worn and the valve head was dished/mushroomed and 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 that the spring contacted. The spring was worn flat on the side that contacted the washer. Borescope examinations of the remaining cylinders showed that the No. 6 cylinder exhaust valve face displayed uneven heat damage consistent with a failing valve. Review of the airframe and engine maintenance records showed that the airplane’s most recent annual inspection was completed on September 25, 2022. RDK was equipped with three runways; runway 5/23, which was 5,100 ft long by 75 ft wide; runway 17/35, which was 2,901 ft long by 60 ft wide; and runway 13/31, which was grass and measured 2,050 ft long by 210 ft wide. GPS instrument approach procedures were available for runways 5 and 17. The pilot reported that the engine began to run rough during the cross-country flight, and the pilot diverted to a nearby non-tower-controlled airport, where he flew the RNAV (GPS) approach to runway 5, the airport’s longest runway. During the descent and approach, the air traffic controller informed the pilot that runway 5 was closed; however, the pilot proceeded to land, and the airplane impacted a barricade and ground equipment, which resulted in substantial damage to the left wing. Examination of the engine found excessive combustion products on the No. 4 cylinder exhaust valve. The deposits wore the valve guide, which resulted in the improper seat of the valve, abnormal valve operation, and fatigue failure of the valve face. The excessive combustion product deposits were most likely due to a rich fuel/air mixture, which prevented the cylinder from reaching the temperature required to ensure that lead combustion products were expelled from the cylinder with the exhaust gas. Review of the airplane’s maintenance records revealed that the engine was 15 days overdue for an annual inspection. Had the required inspection had been performed on time, the exhaust valve issues likely would have been discovered before the accident occurred. Source: NTSB Aviation Accident Database Retrieved: 2026-02-12

NTSB Findings

FAA avdata. C = Cause, F = Factor.

• — Aircraft-Aircraft power plant-Engine (reciprocating)-(general)-Not serviced/maintained
• — Personnel issues-Task performance-Maintenance-Scheduled/routine maintenance-Pilot