CEN17LA014

The student pilot reported that he was returning from a solo flight when the engine "started failing." The engine speed decreased to about 1,500 rpm with a "significant" vibration. The pilot's efforts to restore engine power were unsuccessful, and the engine ultimately lost total power. He subsequently conducted a forced landing to a plowed field, during which the airplane nosed over. A postaccident examination of the engine revealed that the No. 2 cylinder exhaust valve was stuck in the "full open" position. Disassembly of the cylinder revealed that the exhaust valve stem exhibited carbon deposits consistent with the stuck valve condition. No other engine anomalies were noted.

On October 8, 2016, about 1840 central daylight time, a Cessna 150M airplane, N704LE, was substantially damaged during a forced landing following a loss of engine power near Beasley, Texas. The student pilot was not injured. The airplane was registered to and operated by private individuals under the provisions of 14 Code of Federal Regulations Part 91 as a solo instructional flight. Day visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The flight originated from the Wharton Regional Airport (ARM), Wharton, Texas, about 1610. The intended destination was the Sugar Land Regional Airport (SGR), Sugar Land, Texas.The pilot stated that he departed SGR about 1530 and flew to Eagle Lake Airport (ELA) where he conducted some practice takeoffs and landings. He then flew to ARM, conducted some additional takeoffs and landings, and refueled the airplane. He reported conducting a preflight inspection at that time and observed no anomalies. After takeoff, he conducted practice maneuvers in the local area for about 30 minutes before deciding to return to SGR. The pilot stated that while cruising at 2,500 ft mean sea level en route to SGR, the engine "started failing." The engine speed decreased to about 1,500 rpm, with a "significant" vibration. His efforts to restore engine power were unsuccessful and the engine ultimately lost power completely. He executed a forced landing to a plowed agricultural field. During the landing, the airplane nosed over, resulting in damage to the vertical stabilizer, rudder, and left wing. A postaccident examination of the engine revealed that the no. 2 cylinder exhaust valve was stuck in the full open position. Disassembly of the cylinder determined that the exhaust valve stem exhibited carbon deposits consistent with the stuck valve condition. No other anomalies with respect to the no. 2 cylinder or the remainder of the engine were observed. Maintenance records indicated that the engine was overhauled in April 2002. At that time, the engine had accumulated 3,492 hours total time. The overhauled engine was installed on the accident airplane in May 2002, at a recording tachometer time of 3291.9 hours. According to the records, the most recent annual inspection was completed on December 18, 2015. A maintenance entry, dated February 26, 2016, noted that an exhaust valve leak on cylinder no. 4. The exhaust valve was subsequently replaced. The final entry was dated April 8, 2016, and noted that the no. 2 cylinder spark plugs were cleaned. The maintenance records did not contain any subsequent entries. At the time of the examination, the airplane recording hour (Hobbs) meter and tachometer indicated 2373.4 hours and 4131.60 hours, respectively. The engine manufacturer's recommended overhaul interval was 1,800 hours or 12 years. Although more than 14 years had elapsed since the overhaul, Federal Aviation Administration regulations do not require compliance with an enginemanufacturer's recommended time-between-overhaul (TBO) interval.