On October 21, 2012, about 1330 eastern daylight time, a Cessna 150H, N7250S, was substantially damaged during a forced landing after takeoff from Mansfield Municipal Airport (1B9), Mansfield, Massachusetts. The certificated flight instructor (CFI) and student pilot were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the instructional flight, which was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.
According to the CFI, the purpose of the flight was to practice takeoffs and landings at 1B9 and then proceed to a practice area for "aircraft familiarization." The student performed the first landing to a full stop. The second landing attempt was aborted, and another traffic pattern was completed. The CFI "assisted" the subsequent touch-and-go landing. The landing was successful, the flaps were retracted to 20 degrees, carburetor heat was closed, and full engine power was applied. The airplane climbed as expected at 600 feet per minute and the flaps were retracted fully when the airplane climbed above treetop height.
The CFI stated that when the airplane reached 250 feet above ground level, it "stopped climbing." He assumed control of the airplane, verified the position of the engine controls, and despite adjusting airspeeds between best rate and best angle of climb, the airplane continued to descend until it settled into trees off the departure end of the runway, resulting in substantial damage to the empennage and tail sections. The airplane came to rest in the trees, and the occupants climbed down from the airplane uninjured. According to the Federal Aviation Administration (FAA) aviation safety inspector who responded to the accident site, the airplane had been removed from the trees by local authorities, and was placed inverted on the ground. As a consequence, all residual fuel drained from the airplane, and no fuel was retained for examination or testing. Examination of the airframe revealed no pre-impact mechanical anomalies.
The CFI held a commercial pilot certificate with ratings for airplane single engine land, multi-engine land, and instrument airplane. He also held a flight instructor certificate with a rating for airplane single engine. He reported 1,730 total hours of flight experience, of which 53 hours were in the accident airplane make and model.
At 1352, the weather reported at Taunton Municipal Airport (TAN), 11 miles southeast of 1B9, included winds from 290 degrees at 10 knots, variable between 270 and 330 degrees. There were scattered clouds at 4,800 feet with 10 miles visibility. The temperature was 10 degrees C and the dew point was 5 degrees C.
Review of Advisory Circular 91-51A EFFECT OF ICING ON AIRCRAFT CONTROL AND AIRPLANE DEICE AND ANTI-ICE SYSTEMS states in paragraph 5 DISCUSSION b. " There are two kinds of icing that are significant to aviation: structural icing and induction icing....c. Small aircraft engines commonly employ a carburetor fuel system or a pressure fuel injection system to supply fuel for combustion. Both types of induction systems hold the potential for icing which can cause engine failure. (1) The pilot should be aware that carburetor icing can occur at temperatures between 13 degrees Celsius (C) (20 degrees Fahrenheit (F) and +21C (70F) when there is visible moisture or high humidity. This can occur in the carburetor because vaporization of fuel, combined with the expansion of air as it flows through the carburetor, causes sudden cooling, sometimes by a significant amount within a fraction of a second. Carburetor ice can be detected by a drop in rpm in fixed pitch propeller airplanes and a drop in manifold pressure in constant speed propeller airplanes. In both types, usually there will be a roughness in engine operation. Some engines are equipped with carburetor heat for use in both prevention and removal of ice."
According to a carburetor icing probability chart, the atmospheric conditions at the time of the accident were conducive to serious icing at any power setting.
The engine was removed from the airframe and shipped to the manufacturer for examination and a test run under the supervision of an NTSB investigator. On February 28, 2013, the engine was placed in a test cell where it started immediately, accelerated smoothly, and ran continuously at rated power. The engine was shut down and restarted “several times” with the same result each time.