Separation Anxiety

If there were some way I could make a series of trips back in time to change things, one of the stops on my itinerary would be to somehow infiltrate the small cadre of early pilots and airplane designers to convince them to use a word other than stall to describe what happens when a wing exceeds its critical angle of attack. The word obviously has numerous other applications, and using it for this purpose has confounded student pilots and television news anchors ever since. That said, Im not sure what should replace it, and remain open to suggestions.

Editorial Staff

Sunday, September 23, 2018 at 12:00 AM ET

Verified

Key Takeaways:

Misunderstanding the critical angle of attack (AoA), exacerbated by the ambiguous term "stall" and the limitations of "stall speed," is a primary cause of loss-of-control in-flight (LOC-I) accidents, particularly during low-altitude maneuvers.
"Stall speed" is an imperfect and context-dependent measure, only truly relevant in unaccelerated flight; AoA is the direct determinant of lift loss due to flow separation. Pilots without AoA indicators must maintain ample airspeed margins when maneuvering.
Banking and turning significantly increase the risk of exceeding the critical AoA due to factors like increased G-loading, the need for nose-up pitch to maintain altitude, differential wing speeds, and aileron deflection, all of which can precipitate flow separation and potential spin entries.

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If there were some way I could make a series of trips back in time to change things, one of the stops on my itinerary would be to somehow infiltrate the small cadre of early pilots and airplane designers to convince them to use a word other than “stall” to describe what happens when a wing exceeds its critical angle of attack. The word obviously has numerous other applications, and using it for this purpose has confounded student pilots and television news anchors ever since. That said, I’m not sure what should replace it, and remain open to suggestions.

After all, what single word, if any, concisely describes what happens when air flows over an airfoil at low angles of attack but then separates and stops flowing as that angle of attack exceeds a specific value? How to explain that aerobatic and inverted flight depend on excess power and brute force as much as they do training and practice? That there’s no magic geometry exempting the wing from its behavior at high angles of attack? Why is any of this a concern to us?