On September 6, 2013, about 1754 eastern daylight time, an ERCO Ercoupe 415-D, N3940H, was substantially damaged during a forced landing near Beaver County Airport (BVI), Beaver Falls, Pennsylvania. The airline transport pilot and passenger were not injured. The airplane was registered to and operated by a private individual under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and no flight plan was filed. The flight was originating at the time of the accident and was destined for North Central West Virginia Airport (CKB), Clarksburg, West Virginia.According to the pilot, he had flown in from his home base earlier that day uneventfully. The pilot conducted a preflight before his return back to CKB and noted no anomalies. After takeoff while climbing though 200 feet above ground level (agl) the engine "began to run rough." The pilot attempted to turn back towards the airport and halfway through a 180-degree turn, the engine had a loss of total power. The pilot was unable to maintain altitude and executed a forced landing to a field, resulting in substantial damage to both wings.
An examination of the engine assembly by a Federal Aviation Administration (FAA) inspector revealed no anomalies were noted within the induction, carburetor and fuel systems. The airplane was equipped with a Continental C75 series 75-hp engine and according to the FAA inspector it flew approximately 60 hours since the last inspection. The logbooks were not available for review by the NTSB. During the examination approximately 18 gallons of blue fluid, similar in color to 100LL aviation fuel, was discovered in the header tank.
Further examination of the engine revealed that the number 3 exhaust valve was stuck in the open position and an engine run was not performed. No internal engine damage was noted as a result of the stuck valve. Internal examination of the engine revealed that the valve train was intact and rotation of the crankshaft by hand achieved valve train continuity and compression on cylinders number 1, 2 and 4. Examination of the magnetos revealed that spark was obtained on all ignition leads. The top and bottom spark plugs were removed and it was noted that the numbers 2 and 4 cylinder spark plugs were carbon fouled. The other spark plugs exhibited normal wear signatures when compared to the champion spark plug chart.
The number 3 cylinder was removed and an excessive amount of coking was noted on the mid-span of the bore of the valve guide. An examination of the engine oil revealed that the oil was free of debris and the quantity was at the operational level.
A review of the Continental Motors safety bulletin (SB) M77-3 stated that "100LL was an acceptable alternative fuel and continued on to indicate that the amount of tetraethyl lead in these higher grade fuels had increased the lead build up and fouling of spark plugs along with valve erosion incidents reported on some lower compression engines. When using this fuel, exhaust valve sticking could result from lead salt accumulation in the lubricating oil. Under such circumstances, an exhaust leak between the exhaust elbow flange and the exhaust port face was possible, which resulted in localized cylinder head overheating and subsequent exhaust valve and guide distress." Further review of SB M77-3 revealed that it is recommended that regular 50 hour oil changes be implemented to reduce such accumulation. No record of 50 hour oil changes were noted in the engine logbook book as stated by the FAA inspector. It was also recommended that spark plugs should be rotated every 50 hours of operation and cleaning/rotation every 100 hours.
A review of the FAA chart, titled "Conditions Favoring Carb Ice Formation," indicated that with the ambient temperature and dew point, "serious icing at glide power" was probable at the time of the accident."