Egremont, MA, USA
N98550
PIPER J3C-65
The pilot reported that the accident flight was the first flight in the airplane in 6 months. During the initial climb, the engine experienced a partial loss of power. The pilot checked the magnetos and carburetor heat but was unsuccessful in his attempts to regain full engine power. Subsequently, he chose to land the airplane between two houses. A postaccident engine compression test revealed that the Nos. 1 and 4 cylinders had low compression. The No. 1 rocker cover was removed, and the rocker arm was tapped with a mallet, which brought its compression to within normal range. Disassembly of the No. 4 cylinder revealed that it was leaking past the exhaust valve and through the exhaust system. In addition, disassembly revealed a scored intake valve stem and valve guide. The intake valve would not operate and had to be forcefully removed from the valve guide. According to the engine overhaul manual, scored valve stems can cause the engine to produce low power. The pilot did not report performing any of the procedures to return the engine to service from indefinite storage (that is, more than 90 days). Therefore, it is also likely that the engine was never prepared for indefinite storage and, thus, was not stored improperly for the 6 months it was not used before the accident flight. During storage, the No. 4 intake and exhaust valves most likely became lodged in the valve guides, which resulted in a partial loss of engine power and subsequent forced landing to a field. It is likely that, if the engine had been properly stored, the recommended lubrication would have prevented the valves from sticking and scoring and that, if the engine had been properly removed from storage, the scored valves may have been detected and replaced, either of which action could have prevented the accident.
On July 5, 2011, about 1700 eastern daylight time, a Piper J3C-65, N98550, registered to a private individual, experienced a partial loss of engine power and collided with trees shortly after takeoff from the Walter J. Koladza Airport (GBR), Great Barrington, Massachusetts. The personal flight was operated under the provisions of Title 14 Code of Federal Regulations Part 91 with no flight plan filed. Visual meteorological conditions prevailed. The airline transport pilot was not injured and passenger received minor injuries. The flight was originating at the time of the accident. According to the pilot, the accident flight was the first flight in the airplane in 6 months and he performed an extensive engine run up, visually checked the fuel level and quality, noted 7 gallons of fuel prior to takeoff, and did not note any anomalies with the airplane. Then, he performed a "normal" takeoff and about 150 feet above ground level, the engine rpm decreased from takeoff power, around 2200 rpm, to 1700 rpm. The pilot decreased the pitch angle of the airplane and began searching for a place to land. He unsuccessfully attempted to regain full engine power by checking the magnetos and the carburetor heat. In addition, the pilot noted the gauges that indicated the oil pressure and temperature were within "normal" ranges. He elected to land the airplane between two houses. During the landing roll, the airplane subsequently struck underbrush and trees, and then came to rest in trees and foliage. Examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed that the airplane came to rest about 3,000 feet from the departure end of runway 29. The fuselage skin was punctured by a tree branch. A fuselage tube was broken at the lower fuselage tubing cluster and the tube was bent aft. The left wing leading edge was impact damaged and dented in several locations. The upper engine cowl and engine baffling was impact damaged. The carburetor was examined and fuel was noted inside the carburetor and there was no debris in the fuel screen. The tachometer located in the cockpit indicated time of 689.6 hours. According to FAA records, the airplane was manufactured in 1946, and most recently registered to an individual in 2010. It was equipped with a Continental Motors C90-8F, 90-horsepower, engine. The most recent annual inspection was performed on December 10, 2010, and at that time it had accumulated 1,776 total hours of flight time and a tachometer time of 689 hours. In addition, the mechanic who performed the annual inspection completed a compression check on the engine cylinders. The compression test results indicated that the cylinders had compression that ranged from 74 to 78. The most recent overhaul of the engine was noted as June 5, 1994, at a tachometer time of 221.5 total hours. A postaccident engine examination revealed that the No. 2 and No. 3 cylinders did not display any anomalies when a compression test was performed. During the compression test, cylinder No. 1 was leaking out of the exhaust valve through the exhaust system and resulted in a compression ratio of 50/80. The No. 1 rocker cover was removed and the rocker arm was "tapped" with a mallet. A compression test was performed again to the No. 1 cylinder and the compression came up to a ratio of 60/80. The No. 4 cylinder compression test resulted in a compression ratio of 42/80. Disassembly of the No. 4 cylinder revealed that the exhaust valve was leaking out through the exhaust system. In addition, it revealed a scored intake valve and valve guide. The intake valve would not operate and had to be removed from the valve guide with a mallet and drift. According to the engine overhaul manual, in a section labeled "engine troubles and service repair," it indicated that if the engine produced low power, it could be a result of scored valve stems. In addition, the engine overhaul manual stated "obviously even then proper steps must be taken on engines used infrequently to lessen the possibility of corrosion. This is especially true if the aircraft is based near the sea coast or in areas of high humidity and flown less than once a week. In all geographical areas the best method of preventing corrosion of the cylinders and other internal parts of the engine is to fly the aircraft at least once a week long enough to reach normal operating temperatures which will vaporize moisture and other by-products of combustion. Aircraft engine storage recommendations are broken down into the following categories: Flyable Storage (7 to 30 days) Temporary Storage (up to 90 days) Indefinite Storage." Indefinite storage of the engine included a procedure of replacing the engine oil with oil that has anticorrosive properties, installing cylinder dehydrator plugs, sealing all openings in the engine. The process of returning the engine to service after storage included removing the engine seals, removing the cylinder dehydrator plugs, draining the corrosion preventive mixture and reservicing the engine with the recommended lubricating oil. The entire process can be found in the engine manual excerpt in the docket for this case.
A partial loss of engine power due to the No. 4 intake and exhaust valves becoming lodged in the valve guides, which resulted from a lack of use, improper engine storage preparation, and improper return to service from indefinite storage.
Source: NTSB Aviation Accident Database
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