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Aviation 101: Stall During Final-Approach Turn
![the aircraft stalled, descended and struck the ground](/web/20071226060218im_/http://www.tc.gc.ca/CivilAviation/SystemSafety/Newsletters/tp185/3-98/images/019.jpg)
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 Boards 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 pilots 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
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