Engine Malfunction Leads to Forced Landing and Nose-Over in Nebraska (N494SP)

Event Narrative

According to the pilot, he was approximately 20 miles south of Cambridge, Nebraska, at 6,500 feet mean sea level when his engine began to run rough and the airplane started to lose altitude. The pilot immediately turned toward the airport and declared an emergency. He planned to land on runway 32, estimating the winds from the southwest. As he approached, he realized he was high and executed a right 360-degree turn to lose altitude. Still high after the turn, he decided his best option was to land on runway 14. When he turned on final for runway 14, the pilot realized that he was on a downwind approach. He decided that he had no option but to continue. The pilot reported great difficulty in getting the airplane onto the runway, bouncing several times. It became apparent to him that he would not stop on the runway. "I decided to try to divert to [a] plowed field to the left of the runway ... I used the throttle to boost the plane over a road and a fence. Once clear I chopped the power and stalled the plane into the field." After touchdown, the airplane nosed over.

Post-Accident Examination

An examination of the airplane's engine revealed that the intake and exhaust valve push rod tubes were pushed upward and off on the number 2 cylinder. The intake valve push rod was bent upward, and the exhaust valve push rod was broken 5 inches outward from the tappet seat. Examination of the airplane's other systems revealed no anomalies.