NTSB Factual Report

On December 4, 2014, about 1100 eastern standard time (EST), a Cessna 205, N8296Z, was force landed in a farm field following a total loss of engine power during the initial climb from Sussex Airport, Sussex, New Jersey (FWN). The commercial pilot had minor injuries and five passengers were not injured. The airplane was substantially damaged. The airplane was registered to Markelwin Aviation LLC and was operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a skydiving flight. Day, visual meteorological conditions prevailed, and no flight plan was filed. The flight was originating at the time of the accident.

The pilot reported the following. About 1,200 to 1,300 feet above mean sea level, or about 800 to 900 feet above the ground, during the initial climb, a "mechanical failure" of the engine occurred. Due to the low altitude, he force landed the airplane in a muddy farm field, south of the airport. The airplane's nose gear struck a ditch and the airplane nosed over before coming to a stop. The pilot and passengers exited the airplane without further incident.

An inspector with the Federal Aviation Administration responded to the accident site and examined the wreckage. The aft fuselage and empennage exhibited structural damage from impact forces. The propeller was bent aft and the engine remained attached at the firewall. The engine turned freely when the propeller was rotated manually.

On December, 17, 2014, the engine was test run on the airframe, which was equipped with a digital engine monitor, displaying EGT for each cylinder. Due to vibration as a result of impact damage, the engine was not run higher than 1,700 rpm. During the run, the left side cylinders (numbers 2, 4, and 6) experienced a drop in EGT while the right side of the engine ran within the normal range. Black exhaust smoke was observed from the left side engine exhaust manifold. After the test run, the fuel nozzles for the left side of the engine were observed to be clogged with a black substance and the spark plugs were soot-covered. The fuel manifold valve was opened and no anomalies or obstructions were observed. Additionally, each spark plug lead produced spark when the propeller was rotated by hand. The fuel nozzles and spark plugs were then cleaned and the engine was test run again, with the same result of the left side exhibiting significantly less EGT verses the right side (200 degrees F versus 1,000 degrees F) after about 1 minute of operation. Prior to the EGT drop, a magneto check was performed at 1,700 rpm with no anomalies noted. After the second test run, the air intake and exhaust were inspected and observed to be free of obstructions. Some oil was noted inside the number 2 cylinder.

The engine was shipped to the manufacturer's facility for further examination. After an initial inspection, the engine was prepared for a run in the test cell. Once installed, the engine started on the first attempt without hesitation. The engine speed was brought to 1,000 rpm to warm up the engine to normal operating temperatures. The engine was run at 1,200 rpm for five minutes to stabilize. The engine throttle was advanced to 1,600 rpm, 2,100 rpm, and 2,450 rpm and held for five minutes at each rpm setting to stabilize. The engine throttle was then advanced to the full open position and the engine began to "stumble" and lose power.

Investigators then began troubleshooting the fuel system. Subsequent engine runs would result in the engine only being capable of attaining 1,800 rpm. Further troubleshooting revealed both number 2 cylinder intake valve springs were broken. Visible rust was observed on the surfaces of the springs. The broken valve springs were replaced and the engine was run again. After replacing the valve springs, the engine was capable of operating normally at full power. The engine throttle was rapidly advanced from idle to full throttle six times, where it performed normally without any hesitation, stumbling or interruption in power. No further anomalies noted that would have prevented normal operation or production of rated horsepower.

The fractured inner and outer intake valve springs from the number 2 cylinder were subsequently examined by investigators. Both springs showed fatigue fractures originating from rust pits on the surfaces.

A review of the engine maintenance logbooks revealed that a 100 hour/annual inspection was completed on October 14, 2014, at 7,857.8 hours tachometer time. About 13 hours of operating time had accrued since the last inspection of October 14. About 1,501 hours had accumulated on the engine since its last major overhaul. According to the engine manufacturer's operating manual, under the 100-hour inspection procedures, it states, "Remove valve rocker covers, and inspect visible parts of the valve mechanism for breakage and lack of lubrication. All parts should be covered with oil."

NTSB Probable Cause

Maintenance personnel’s inadequate inspection of the No. 2 cylinder valve area during the most recent annual inspection, which resulted in the in-flight failure of the intake valve springs due to rust on the spring surfaces and subsequent fatigue cracking.