MIA02LA149 · Cessna 150M

The student pilot stated that he was conducting a long solo cross-country flight, proceeding east to La Belle, Florida, and while en route the airplane's engine started to sound as if it was "back-firing, missing, or a combination of the two." He stated that engine power decreased, but all gages exhibited normal indications. As he tried advancing the throttle to increase engine power in an attempt to maintain altitude, he said the engine performed worse. He said he was afraid he would blow the engine over an unsuitable landing area, so he veered north to follow Highway 80 in case the engine ceased operating. As he followed the highway he said the airplane continued to loose altitude, and he opted to make a landing on a straight portion of Highway 80, about 2 miles west of La Belle, Florida. He said he chose to land on the north berm of the highway and during touchdown the airplane skipped and started skidding. The right wing impacted a palm tree and spun the airplane around causing substantial damage. The student stated that he never applied carburetor heat, or even considered applying carburetor heat because the loss of power he was experiencing was not what he had associated with carburetor ice. He stated that he had come to expect a steady loss of engine power, rather than the engine back firing and missing as had happened. After recovery, the engine was examined by an FAA licensed airframe and powerplant mechanic, with an inspection authorization rating, and no anomalies were noted. The mechanic stated that during the examination there was good compression on all cylinders, and during test runs, the engine developed power normally. According to the carburetor icing chart, conditions were conductive to the formation of visible icing while the airplane was being operated at glide and cruise power settings.

Verbatim NTSB analysis and probable cause from the NTSB dataset