Bellanca 7GCBC N8737V

The pilot reported that, during the preflight inspection before the airplane’s first flight of the day, which was also its first flight in 6 months during which it remained outside, he sumped about 32 ounces of fuel from each wing, the gascolator, and the lower sump. During taxi to the fuel pumps to refuel, he smelled smoke, which he thought might have been due to a bird's nest, so he and the airport manager removed the top and bottom cowls and thoroughly inspected the area around all the cylinders and the bottom cowl area and found no nests He subsequently fueled the airplane and conducted an engine run-up, and all indications were normal and remained normal throughout the takeoff roll. However, after taking off and as the airplane was about 500 ft above ground level (agl), the pilot noticed the rpm decreasing. He applied carburetor heat, but the engine rpm continued decreasing, so he decided to turn left toward the airport and subsequently landed uneventfully. He then completed a walk-around inspection with no anomalies noted. The pilot then asked an airframe and powerplant mechanic to help him look for anything that might have caused the decrease of rpm. He and the mechanic inspected the engine and found no nest remnants in the induction airbox or associated ducting. The mechanic saw that the No. 3-cylinder exhaust manifold was hanging with no gasket, washers, or nuts present and that the intake cuff was found moderately deteriorated, incorrectly installed, and clamped to the airbox instead of the cowl. The mechanic examined the airbox and venturi, and found no obstructions, and he did not see anything that would have prevented fuel going to the carburetor. The mechanic noted that the main fuel supply line was fabricated out of unreinforced automotive fuel or coolant hose and that the line was pinched nearly closed due to a fitting misalignment. Subsequently, a standard aviation fuel hose and fitting were installed. The pilot then conducted a full-throttle engine run-up and a walk-around inspection with no anomalies noted. He checked the fuel level, and it showed over half a tank. The pilot proceeded to taxi the airplane to the end of the taxiway and conducted a full-throttle run-up for about 45 seconds and a walk-around inspection with no anomalies noted. After a normal takeoff and just after clearing the end of the runway and the beginning of a lake and as the airplane was about 300 ft agl, the pilot noticed the engine rpm decreasing “quickly.” Unable to reach the airport, the pilot chose to ditch the airplane in the lake. The pilot reported that, just before water impact, the engine “stopped producing any usable power.” The pilot egressed the airplane and was subsequently rescued by first responders. The airplane sank in 44 ft of water and was recovered about 24 hours later. Although postaccident examination of the airframe and engine revealed no evidence of any preaccident mechanical malfunctions or failures that would have precluded normal operation, it is possible that some evidence that could have helped determine the reason for the two loss of engine power events might have been lost due to its submersion in water for 24 hours and/or during the recovery process. Therefore, based on the available evidence, the investigation could not determine what led to the partial loss of engine power during either of the two flight’s takeoffs.

Quoted verbatim from the NTSB record.