Introduction
On March 18, 2014, at 1043 eastern daylight time, a Cessna 150M airplane, registration N9432U, was substantially damaged when it struck terrain near Greenwood, Indiana. The flight instructor sustained minor injuries and the student pilot received serious injuries. The airplane was privately registered and operated by Jeff Air Pilot Services, LLC under Part 91 without a flight plan. The local instructional flight departed Greenwood Municipal Airport at 1015, with day visual meteorological conditions prevailing.
Flight History
According to the flight instructor, the student had approximately 30 flight hours but had not flown in several years. No engine anomalies were noted during taxi and run-up; however, carburetor heat application during run-up caused a drop in engine speed. After takeoff, the flight proceeded southeast to perform basic maneuvers at altitudes between 2,500 and 3,000 feet mean sea level. The student executed slow flight, two approach-to-landing stalls, and one takeoff/departure stall. Upon recovering from the takeoff/departure stall, a partial loss of engine power occurred. Full throttle produced no increase in power, and the engine continued running at a reduced setting. The instructor took control, established best glide speed, and verified magneto operation, fuel selector position, and that the mixture and throttle were full forward. Carburetor heat application did not noticeably affect engine operation. The instructor initiated a forced landing to an agricultural field but did not recall the impact.
The student pilot reported that after the takeoff/departure stall, he made a couple of turns before the instructor directed him back to the airport. Engine speed was about 1,800 RPM during the turns, causing a loss of altitude and airspeed. When the student advanced the throttle fully forward, the engine did not respond. The instructor assumed control but could not restore power. The student noted significant vibration as engine operation deteriorated. The instructor proceeded with the forced landing; however, just before flare, approximately 25–30 feet above ground, engine power suddenly increased, causing the airplane to pitch up and enter an aerodynamic stall, followed by ground impact. After the accident, the student turned off the magneto switch and master electrical power switch.
Wreckage Examination
FAA inspectors examined the wreckage at the site and after recovery. The airplane sustained substantial damage to the fuselage, empennage, and both wings. Flight control continuity was confirmed from cockpit controls to surfaces. Fuel was present in both wing tanks, the fuel strainer, and the carburetor float bowl; the carburetor inlet screen was not obstructed. The cockpit throttle and mixture controls were full forward, and the carburetor heat control was extended and bent downward. The engine produced suction and compression on all cylinders during crankshaft rotation, with valve train continuity and proper magneto function. Upper spark plugs showed normal operation. The carburetor throttle arm, mixture control cable, and carburetor heat control cable were separated, but these separations were consistent with ground impact damage. No evidence of preimpact mechanical malfunction or abnormalities that would have prevented normal engine operation was found.
Weather and Carburetor Icing Conditions
The nearest weather station, Indianapolis International Airport, reported at 1049: wind 160° true at 13 knots, visibility 10 miles, broken ceiling at 1,800 feet agl, temperature 4°C, dew point -1°C, altimeter 29.93 inHg. FAA carburetor icing probability chart indicated a serious risk of carburetor ice accumulation at cruise and descent power settings. According to the FAA Pilot's Handbook of Aeronautical Knowledge, when conditions are conducive to carburetor icing, heat should be applied immediately and left on until ice is removed; partial or insufficient heat may worsen the situation.
Additional Observations
Earlier that morning, an aviation mechanic performed an engine run on another Cessna 150 at the departure airport. At about 1,800 RPM, he noticed a 200 RPM drop consistent with carburetor icing and applied carburetor heat, which restored power. He encountered similar symptoms at least two more times. In a later interview, the flight instructor confirmed that carburetor heat was not used during any of the training maneuvers conducted at reduced power settings (slow flight, two approach stalls, one departure stall). He also noted that he had not previously experienced carburetor icing in this model but recalled a similar power loss event in the same airplane the previous month. Maintenance records attributed that earlier event to an excessively low ground-idle throttle setting, which was subsequently adjusted; no further engine anomalies were recorded after the adjustment.