ERA21LA284

After performing flight training maneuvers for about 30 minutes, the instructor and student returned to the airport to practice short/soft field takeoffs and landings. After the first full-stop landing, the flight instructor recalled applying carburetor heat during the landing and taxi back for the next takeoff. During the student’s subsequent short field takeoff, the airspeed did not increase as expected while in ground effect and the instructor asked the student why he was not climbing. The student replied that he didn’t know and relinquished the controls to the instructor. The instructor determined that the engine was not producing enough power to maintain level flight and that they were too low to troubleshoot. As the airplane descended and the airspeed decreased, she lowered the nose and made a forced landing into trees, which resulted in substantial damage to the wings and fuselage. After the accident the flight instructor stated she thought the cause was carburetor ice. The temperature and dewpoint at the time of the accident were conducive to serious icing at glide power, and carburetor ice likely accumulated during the approach and previous landing. Although the instructor recalled applying carburetor heat during taxi there may not have been sufficient time to melt all or any accumulated carburetor ice.

On July 10, 2021, about 2010 central daylight time, a Cessna 150F, N8172S, was substantially damaged when it was involved in an accident near Elba, Alabama. The flight instructor and student pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. According to the flight instructor, after conducting maneuvers for about 30 minutes, they returned to Carl Folsom Airport (14J) to conduct short/soft field landings and takeoffs. After the first successful full-stop landing, they taxied back to the runway and set up for a short field takeoff and, according to the flight instructor, she applied carburetor heat during the short taxi. Shortly after rotation and liftoff, the airspeed was not increasing as they flew in ground effect. The flight instructor asked why they weren’t climbing, and the student stated, “I don’t know, you have the controls.” The flight instructor took the control of the airplane and performed a shallow right climbing turn to avoid the trees at the end of the runway. The flight instructor stated there was no time to perform any troubleshooting of the engine because they were “barely” flying, and she needed to “just fly the airplane.” The engine was operating but not producing sufficient power to maintain level flight. They were flying over the treetops as the airspeed continued to decrease and the airplane started to descend. The flight instructor pushed the nose over to avoid a stall and landed the airplane in the trees. The airplane wreckage was located about 1,000 ft west southwest of the departure end of the runway in heavy wooded terrain and brush. Postaccident examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed that the airplane came to rest in a nose-down attitude and was tilted to the right. Both wings were bent aft, and the airframe sustained substantial damage. The left fuel tank was breached, and the right tank remained intact and contained fuel. The inspector was unable to examine the engine due to the airplane’s orientation and surrounding terrain. After the accident, the instructor told the FAA inspector that she had been thinking about what caused the accident and stated she thought it might be carburetor icing. The wreckage was recovered to an aviation salvage company and promptly sold. According to the salvage company that took possession of the wreckage, the engine was in excellent working condition and was subsequently sold to a private individual. A review of the local area meteorological data showed that the 1958 recorded weather observation at Shell Army Heliport (SXS) Fort Novosel, Alabama, about 12 miles southeast of the accident location, included wind from 240° at 3 knots, 9 miles visibility, clear skies, temperature 24°C, dew point 22°C; and an altimeter setting of 30.08 inches of mercury. The carburetor icing probability chart from FAA Special Airworthiness Information Bulletin (SAIB): CE-09-35 CarburetorIcing Prevention, showed a probability of serious icing at glide power at the temperature and dew point reported at the time of the accident. FAA Special Airworthiness Information Bulletin (CE-09-35) – Carburetor Icing Prevention, stated that: …pilots should be aware that carburetor icing doesn't just occur in freezing conditions, it can occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. Icing can occur in the carburetor at temperatures above freezing because vaporization of fuel, combined with the expansion of air as it flows through the carburetor, (Venturi Effect) 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.