Primary finding
Probable cause
The partial failure of the no. 4 piston from over temperature (detonation).
Investigator assessment
Analysis narrative
While in cruise flight engine suddenly began to run rough and loose power. No unusual noise was associated with the anomaly. Examination of the engine revealed damage to the upper surface of the no. 4 piston. The damage to the piston was consistent with detonation and subsequent ring breakage.
Source record
Factual narrative
On March 28, 1994, at 1420 Alaska daylight time, a wheel equipped Cessna 207 airplane, owned and operated by Spernak Airways, Inc., experienced a loss of engine power while in cruise flight. The airline transport certificated pilot-in-command performed an emergency landing on Sleeper Strip, a private strip located about 4 miles east of Anchorage, Alaska, that is not maintained during the winter. The pilot and his three revenue passengers were not injured and the airplane sustained minor damage. The 14 CFR Part 135 on demand flight last departed Merrill Field Airport, Anchorage, Alaska, at 1415 and the intended destination was Beluga, Alaska. Visual meteorological conditions prevailed and a company VFR flight plan was in effect. The pilot-in-command told the NTSB investigator-in-charge during a personal interview that the airplane was in stabilized cruise flight at an altitude of approximately 1000 feet above the ground when the engine began to run rough and loose power to the point where he could no longer maintain altitude. There were no metallic sounds associated with the engine anomaly. Examination of the engine, a Teledyne Continental IO-540-F, by the NTSB investigator-in-charge revealed substantial damage to the upper surface of the No. 4 cylinder. The cylinder and its associated connecting rod were forwarded to the NTSB's metallurgical laboratory in Washington, D.C. for examination and analysis. The metallurgist's factual report and analysis report are contained in the incident report package. -