CEN14LA161

The flight instructor reported that the airplane sustained a partial loss of engine power after his student completed several training maneuvers at a reduced engine power setting. The subsequent application of full throttle did not increase the engine power, and the engine continued to operate with reduced power. The flight instructor then took control of the airplane and established best glide speed while he verified that the magnetos were operating properly, that the fuel selector was in the "on" position, and that the mixture and throttle were full forward. Applying carburetor heat did not noticeably affect engine operation. The instructor remembered maneuvering toward a nearby field for a forced landing; however, he did not recall the landing or impact with terrain. The student pilot stated that, shortly before flare/touchdown and when the airplane was about 25 to 30 feet above the ground, the engine power increased suddenly, which caused the airplane to pitch up and enter an aerodynamic stall. The airplane subsequently impacted terrain. An examination of the engine did not reveal any preimpact mechanical malfunctions or abnormalities that would have precluded normal engine operation. The atmospheric conditions at the time of the accident were conducive to the accumulation of carburetor ice at cruise and descent engine power settings. Additionally, an aviation mechanic confirmed the existence of carburetor icing conditions at the departure airport within 1 hour of the accident. The instructor confirmed that carburetor heat had not been used during any of the training maneuvers completed at reduced engine power settings. The failure to use carburetor heat while performing flight maneuvers at reduced engine power settings while in conditions conducive to the formation of carburetor ice likely resulted in the partial loss of engine power. The sudden increase of engine power shortly before landing was likely due to a reduction of accumulated carburetor ice following the flight instructor's application of carburetor heat and the increase in ambient temperature as the airplane descended during the forced landing.

On March 18, 2014, at 1043 eastern daylight time, a Cessna model 150M airplane, N9432U, was substantially damaged when it impacted terrain near Greenwood, Indiana. The flight instructor sustained minor injuries and his student sustained serious injuries. The airplane was registered to a private individual and operated by Jeff Air Pilot Services, LLC, under the provisions of 14 Code of Federal Regulations Part 91, without a flight plan. Day visual meteorological conditions prevailed for the local instructional flight, which departed Greenwood Municipal Airport (HFY), Greenwood, Indiana, at 1015. According to the flight instructor, the accident flight was with a new student who had about 30 hours of flight experience, but had not flown in several years. He reported that there were no anomalies with the engine operation during taxi and the pretakeoff engine run-up. Specifically, he noted that the application of carburetor heat resulted in a drop in engine speed during the engine run-up. After takeoff, the flight proceeded southeast of the airport to perform basic flight maneuvers between 2,500 and 3,000 feet mean sea level. The student pilot demonstrated slow flight, two approach-to-landing stalls, and one takeoff/departure stall. Upon recovery from the takeoff/departure stall, the airplane experienced a partial loss of engine power. The instructor stated that the application of full engine throttle did not result in an increase of engine power and that the engine continued to operate at a reduced power setting. The instructor took control of the airplane and established best glide speed while he attempted to restore full engine power. He stated that he verified proper magneto operation, that the fuel selector was in the ON position, and that the mixture and throttle controls were full forward. Additionally, he reported that applying carburetor heat did not noticeably affect engine operation. The instructor then focused on performing a forced landing to a nearby agricultural field; however, he did not recall the landing or impact with terrain. The student pilot reported that after practicing the takeoff/departure stall he completed a couple of turns before the flight instructor told him to turn back toward the airport. He stated that the engine speed was about 1,800 RPM during the turns and, as a result, he lost both altitude and airspeed. He leveled the airplane and attempted to increase engine speed, but the engine did not respond when the engine throttle was advanced to full forward. The instructor then assumed control of the airplane; however, his corrective actions to restore engine power were not successful. The student pilot reported that there was a significant vibration in the airplane as the engine operation continued to deteriorate. The instructor proceeded with the forced landing; however, shortly before flare/touchdown, about 25-30 feet above the ground, the engine power increased suddenly, which caused the airplane to pitch up andenter an aerodynamic stall. The airplane subsequently impacted terrain. Following the accident, the student pilot turned the magneto switch and master electrical power switch to OFF. A wreckage examination was completed by Federal Aviation Administration (FAA) inspectors at the accident site and after it had been recovered to the departure airport. Their examinations established that the airplane sustained substantial damage to the fuselage, empennage, and both wings. There was flight control continuity from the cockpit controls to the respective flight control surfaces. There was fuel located in both wing fuel tanks, the fuel strainer/filter, and in the carburetor float bowl. The carburetor inlet fuel screen was not obstructed with excessive debris. The cockpit throttle and mixture controls were full forward and the carburetor heat control was extended and bent down. The engine produced suction/compression at each cylinder in conjunction with crankshaft rotation. Additionally, valve train continuity and proper magneto function were verified in conjunction with crankshaft rotation. The upper spark plugs were removed and exhibited features consistent with normal engine operation. The carburetor throttle arm, mixture control cable, and the carburetor heat control cable were found separated from their corresponding components; however, the observed separations were consistent with damage associated with ground impact. The examination of the engine did not reveal any evidence of preimpact mechanical malfunction or abnormalities that would have prevented normal engine operation. The nearest aviation weather reporting station was located at Indianapolis International Airport (IND), Indianapolis, Indiana, about 12 miles northwest of the accident site. At 1049, the IND automated surface observing system reported the following weather conditions: wind 160 degrees true at 13 knots, visibility 10 miles, broken cloud ceiling at 1,800 feet above ground level (agl), temperature 4 degrees Celsius, dew point -1 degrees Celsius, altimeter setting 29.93 inches of mercury. The carburetor icing probability chart included in FAA Special Airworthiness Information Bulletin No. CE-09-35, Carburetor Icing Prevention, indicated that there was a serious risk of accumulating carburetor ice at cruise and descent engine power settings. The FAA Pilot's Handbook of Aeronautical Knowledge stated that when conditions are conductive to carburetor icing that carburetor heat should be applied immediately and should be left on until the pilot is certain all the ice has been removed. Additionally, if ice is present the application of partial carburetor heat or leaving heat on for an insufficient time might aggravate the situation. On the morning of the accident, about 0945, an aviation mechanic at the departure airport was performing an engine run on another Cessna 150 airplane to verify that the electrical system was charging properly. During his engine run, at about 1,800 RPM, henoticed the onset of carburetor icing symptoms when the engine speed dropped about 200 RPM. The mechanic applied carburetor heat and the engine speed recovered within several seconds. The mechanic reported that he encountered symptoms of carburetor icing at least two additional times during his engine run. In a follow-up interview, the instructor confirmed that carburetor heat had not been used during any of the training maneuvers that were completed at reduced engine power settings (slow flight, two approach-to-landing stalls, and one takeoff/departure stall). Additionally, the instructor noted that he had not previously experienced carburetor icing in the accident airplane make/model. However, he did report having a similar loss of engine power event in the accident airplane during the previous month. A review of maintenance records indicated that the previous loss of engine power was attributed to an excessively low ground-idle throttle setting. Additionally, the records did not reveal any additional reports of engine anomalies since the engine ground-idle speed adjustment was completed.