Aviation 101:  Stall During Final-Approach Turn

The pilot of a Cessna 150 was planning to take passengers on a local flight but decided to test-fly the aircraft because the alternator had just been replaced. The pilot took off from Runway 22 and climbed to approximately 500 ft., turned back and flew a low pass over Runway 04. He then entered the downwind for Runway 12, flew a low pass over the runway and made a turn back toward Runway 30. Descriptions of the flight path indicated that all turns were steep, between 60° and 90°. At some point during or prior to the last turn, some people reported hearing a loud "pop" sound, and the aircraft made a continuous turn to align with Runway 30. During the final turn, the aircraft stalled, descended and struck the ground. The pilot died as a result of injuries received during the crash.

The Transportation Safety Board’s final report (A96O0153) states that there was no mechanical explanation for the reported "pop" sound and that subsequent laboratory examination showed that the engine tachometer was indicating 2200 rpm at impact. The engine was dismantled and no defects that would have prevented the engine from developing full power were noted. The flaps were in the fully retracted position, which was inconsistent with the pilot’s normal landing configuration. According to the report, the Cessna 150 Pilot Operating Handbook indicates that the aircraft stalls in a wings-level attitude, with flaps up, at 46 to 47 kt. indicated airspeed. In a 60° bank, the stall speed is 66 kt., and, in a 75° bank, it increases to 92 kt. This accident illustrates the low-level stall potential during a final approach turn to a runway with the flaps up, a configuration not usually adopted under normal circumstances. This type of stall, as we all know, is unrecoverable most of the time. Although we all practice flapless approaches and landings under controlled conditions, the circumstances of this accident indicate that this flapless final approach turn was unplanned and precipitated by the events.

As an aside to this story, low passes over runways and steep turns at low altitude are not typically recommended patterns for testing the serviceability of an aircraft. Steep turns are valuable, and fun to practice at high altitude, but unnecessary and dangerous at low altitude. Keep in mind one of the basics of Aviation 101: thou shalt always keep lift under thy wings when off the ground…