An aeroplane can stall at any airspeed, any altitude and any attitude
Indeed! Something I had rammed home during my CPL training as well but had also had experience of during my Aeros training.
The following is from this weeks AOPA newsletter and happens to be about ciritical AoA and stalls.
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CRITICAL ANGLE OF ATTACK
Pilots learn that a stall can occur "at any airspeed, in any attitude, with any power setting," as explained in Chapter 4 of the FAA's Airplane Flying Handbook. How well do you understand this concept?
The typical method of practicing and demonstrating straight-and-level stalls and recoveries is to slow the aircraft down in the takeoff or departure configuration until it reaches the minimum controllable airspeed (MCA) depicted on the airspeed indicator, inducing the stall, and recovering. (See the February 10, 2006, Training Tips article "Pre-solo Stalls.") This is a safe way to demonstrate the effects of exceeding the critical angle of attack. But letting the discussion end there carries the risk of fixing in a student's mind the inaccurate notion that exceeding that angle of attack can be prevented simply by flying above minimum controllable airspeed (MCA). That's not so.
Suppose you are on your final approach glide with flaps down, throttle at idle, and maintaining an indicated airspeed of 65 knots, well above MCA for your airplane. Another aircraft suddenly appears below and in front of you. Your first reaction is to haul back sharply on the yoke to avoid collision. Without decelerating to MCA, the aircraft wing exceeds its critical angle of attack and stalls—unexpectedly and at low altitude. Because this is a so-called accelerated stall, the added lift induces a load on the airframe. To understand maneuvering speed's importance to stall avoidance, see Rod Machado's "A New Look at Maneuvering Speed" in the March 1999 AOPA Flight Training.
A glance at your pilot's operating handbook reminds you that stall speeds increase with bank angle. Practicing a level-flight steep turn, or increasing bank to complete a turn in the pattern, you are surprised to hear stall-warning activation at what seems to be a healthy airspeed. Remember that you are flying a maneuver with a high-load factor, meaning that the aircraft wing is producing horizontally inclined lift to turn the aircraft plus the necessary vertical component of lift to regulate altitude. It is flying closer to its critical angle of attack than in unaccelerated level flight.
Managing angle of attack at any airspeed, attitude, or power setting is the key, as the opening words above remind us.
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J.