ERA21LA384 · Cessna 150 M

The pilot departed his home base and flew to a nearby airport for fuel, where he filled the tanks. Afterward, the pilot departed for a cross-country visual flight rules flight. During the takeoff climb, he noticed that “the angle of attack of the airplane was higher than usual and the climb performance was less than expected.” The pilot surmised that the airplane’s reduced performance was a result of the air temperature (about 30°C) and the full fuel load. He continued the flight and recalled monitoring the gauges because the performance of the airplane had him “concerned.” When the airplane was about 48 miles from the departure airport, he determined that the airplane was “losing performance” and that the airplane would not be able to reach an airport. He elected to perform a forced landing to a field. During the landing flare, the airplane stalled and impacted the ground. The pilot was seriously injured, and the airplane sustained substantial damage to the fuselage and wings.

A postaccident examination of the airframe and engine revealed no preimpact anomalies that would have precluded normal operation. A review of weather records and airplane performance data indicated the airplane’s expected maximum rate of climb would have been 435 ft per minute or greater at altitudes below 4,000 ft.

According to the Federal Aviation Administration’s carburetor icing probability chart, at the surface temperature and dew point during the accident flight, “serious icing at glide power” could be expected. One key symptom of carburetor ice is a reduction in engine rpm, which would result in reduced engine power and climb performance. However, another key symptom of carburetor ice is a roughness in engine operation, which the pilot did not report. He first noticed the decreased performance during the climb, when the engine was likely set for takeoff (full) power. The pilot then determined, while the airplane was flying presumably at a cruise power setting, that the airplane’s performance had decreased such that the airplane would be unable to continue to an airport. Given these presumed power settings along with no reported engine roughness, carburetor icing was likely not a factor in the accident.

A review of the airplane’s maintenance records revealed that, at the time of the most recent engine inspection (performed almost 4 months before the accident), the compression test values for some cylinders were lower than during the previous inspection. Significantly reduced cylinder compression results in reduced engine power and decreased airplane performance. However, results between compression tests can occur. Results depend on a number of variables, including ambient and engine temperatures at the time of the tests; therefore, acceptable values are determined at the time of each inspection. No other conditions related to typical concerns with low compression (such as excessive oil consumption, abnormal appearance or condition of oil, or indications of high crankcase pressure) were noted in the airplane’s maintenance log entries during the previous 3 years. The investigation could not determine whether one or more cylinders experienced progressive wear or another condition that might have resulted in deteriorating compression over time.

Verbatim NTSB analysis and probable cause from the NTSB dataset