CEN23LA036

On November 13, 2022, about 0950 central standard time, a Cessna 152 airplane, N222UM, sustained substantial damage when it was involved in an accident near Manchester, Michigan. The flight instructor and the student pilot were uninjured. The flight was being operated as a 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor stated that they had been in cruise flight with the engine operating about 2,400 rpm when he “felt the power drop.” He then noticed the tachometer showed about 1,300 rpm. He stated that he took the flight controls from the student pilot, applied carburetor heat, and used the checklist to attempt to restore power. At one point, while trying different throttle and mixture settings, the rpm appeared to increase to about 1,500 for about 10 seconds before reducing back to 1,300. The instructor notified air traffic control of the power loss and diverted to the nearest airport. When it became evident they would not be able to reach the airport, he selected a field for a forced landing. During the landing, the nose wheel dug into the soft soil, and the airplane nosed over, which resulted in substantial damage to the vertical stabilizer and rudder. The student pilot stated that after the engine rpm reduced to 1,300, the flight instructor applied carburetor heat, and the engine rpm reduced and then “came back up” but only for a short time. Both pilots stated that the fuel tanks had been topped off the night before, and the airplane was placed in a hangar overnight. Before the flight, they conducted a preflight inspection, which included sumping the fuel tanks, with no anomalies noted. After engine start and taxi, a run-up was accomplished with no anomalies noted. During a postaccident examination, control continuity was established from the cockpit to all flight and engine controls. Fuel was drained from the carburetor and the left and right fuel tanks, and no contaminants were present. The carburetor venturi was inspected with no anomalies noted. The spark plugs were removed and found to be unremarkable. Following removal of the top spark plugs, thumb compression was noted on all cylinders when the propeller was rotated by hand. The magnetos were tested on the airframe and sparking was observed on all leads in firing order. The 0953 weather observation at Ann Arbor, Michigan located 17 from the accident site recorded a temperature of 32° F and a dewpoint of 25°F. Based on the FAA carburetor icing probability chart (Figure 1), the atmospheric conditions at the time of the accident were conducive to the development of serious carburetor icing at glide and cruise power. Figure 1: Carburetor Icing Probability Chart (Source: FAA SAIB CE-09-35)