Accident
On November 6, 2010, about 1310 eastern daylight time, a North American/Schwamm AT-6F, N164US, was substantially damaged after the engine lost power during the approach to Fitchburg Municipal Airport (FIT), Fitchburg, Massachusetts. The airplane collided with terrain short of runway 32 and came to rest inverted in the Nashua River. The certificated commercial pilot, who was the aircraft operator, was killed, and a passenger received serious injuries. Day, visual meteorological conditions prevailed, and no flight plan was filed for the local, revenue sightseeing flight, which originated about 1223 and was conducted under 14 Code of Federal Regulations Part 91.
Aircraft
The airplane was a North American/Schwamm AT-6F, serial number 44-81687-A, powered by a Pratt and Whitney R-1340 AN-1 radial engine rated at 600 horsepower at 2,250 rpm. An annual inspection was performed on January 7, 2010, at a total airframe time of 5,766 hours. Recovered records did not document any recent removal or disassembly of the carburetor.
Pilot
The pilot held a commercial pilot certificate with airplane single-engine land and glider ratings. He reported 2,621 civilian flight hours on his FAA second-class medical certificate application dated April 27, 2010. His pilot logbook indicated a flight review completed on April 24, 2009, in a Cessna 172.
Weather
Weather recorded at FIT at 1252 included wind from 350 degrees at 6 knots, visibility 10 statute miles, clear sky, temperature 8°C, dew point 0°C, and an altimeter setting of 30.11 inches of mercury.
Flight Recorder
The airplane carried a Panasonic HDC-SD1PP high-definition digital video recorder. Two video files were recovered: a 1-minute-26-second pre-accident recording and a 51-minute-55-second recording of the accident flight. The latter was taken from a fixed mount behind the forward windscreen. The video showed the departure, aerobatic maneuvers, and the approach. At 51:33.15, the pilot said "whoops my" as engine noise decreased. At 51:47.15, he stated, "we’re in trouble the engine has stopped for some reason." The last frame at 51:55.03 showed the airplane low and sinking rapidly toward a river.
Wreckage
The wreckage was recovered and examined by NTSB and FAA investigators. Flight control continuity was established from the cockpit to the wing roots and elevator bell crank. Throttle, mixture, and propeller control continuity was confirmed. The fuel selector was found in the right tank position. Both inboard tanks had about 1/8 inch of fuel; outboard bladders were empty. No water or contaminants were found in the tanks. The carburetor had a punctured float bowl; disassembly revealed a dented and cracked float. The propeller was rotated by hand with no binding, and compression was confirmed on all cylinders.
Medical and Pathological Information
A postmortem examination of the pilot at the Office of the Chief Medical Examiner for Massachusetts listed the cause of death as blunt head trauma. Forensic toxicology by the FAA Bioaeronautical Sciences Research Laboratory tested negative for ethanol, cyanide, and carbon monoxide. Acetaminophen was found in urine (27.97 ug/ml) and diphenhydramine in both urine and blood (0.152 ug/ml).
Carburetor Examination
NTSB Materials Laboratory examined the carburetor, a Bendix Stromberg model NA-Y9E1. One float chamber was perforated from external impact; its float was undamaged. The float in the opposite chamber had a fractured solder joint about 0.8 inches long, with corrosion products containing carbon, oxygen, and lead. Lab-fractured exemplar solder joints contained tin, copper, and lead.