The accelerated stall usually surprises a pilot because it occurs at a higher airspeed than a normal stall (in which a wing loading of 1 G is maintained). Remember, a wing can be made to stall at any speed—all that has to happen is for the angle of attack to get high enough. As G-loading increases, so does stall speed. If a wing reaches its critical angle of attack when the wing loading is 2 G, twice normal, the stall will occur at a speed that’s proportional to the square root of the wing loading. The square root of 2 is approximately 1.41, so the stalling speed at 2 G will be 1.41 times what it would be under 1 G conditions. Accelerated stalls are often caused by abrupt or excessive control inputs made during steep turns or pull-ups. If you’re in a dive and pull back with enough suddenness and force to load the airplane to a typical design load factor of 3.8 G’s, you’ll enter an accelerated stall if the airspeed drops below 1.95 times the stall speed at 1 G loading (the square root of 3.8 is approximately 1.95).
One of the most dramatic accidents involving an accelerated stall occurred on September 6, 1985, at General Mitchell International Airport in Milwaukee, Wis. Midwest Express Airlines Flight 105, a DC-9, was taking off from runway 19R at about 3:21 p.m. The weather was clear; visibility was 10 miles. During initial climb, at about 450 feet AGL, there was a loud noise and loss of power associated with the right engine. Investigation would later indicate that there had been an uncontained failure of the engine’s ninth- and tenth-stage high-pressure compressor spacer.