Accelerated Stall: Stall Speed, Bank Angle & Load Factor
An accelerated stall is a stall that occurs above 1 G of load factor. An airplane stalls when the wing exceeds its critical angle of attack. Airspeed is not the cause of the stall; it is one indicator of how much angle of attack is required to produce the necessary lift. An accelerated stall is simply a stall that occurs while the airplane is carrying more than 1 G of load factor.
n = L/W = 1 ÷ cos φ
Here, n is load factor, L is total lift, W is weight, and φ is bank angle. This relationship applies to a coordinated turn in which altitude is being held. It is not a universal “bank-angle equals G” rule for every turning flight condition.
Why load factor increases in a level turn
When the airplane banks, the lift vector tilts with the airplane. Only the vertical component of lift supports weight. To maintain altitude, the pilot must increase total lift until its vertical component once again equals weight:
Rearranging gives L/W = 1/cos φ. At 45° of bank, the required load factor is approximately 1.414 G. At 60°, it is 2 G. If altitude is not held, this simple relationship no longer describes the complete motion.
Why stall speed rises with load factor
At the stall, the wing has reached the maximum lift coefficient available for the existing configuration and condition. From the lift equation, stall speed varies with the square root of the lift requirement. For the same airplane weight, configuration, and maximum lift coefficient:
This is a theoretical aerodynamic relationship, not an aircraft-specific operating limitation. It assumes the same configuration and available maximum lift coefficient.
| Bank angle | Load factor in coordinated level turn | Stall-speed multiplier |
|---|---|---|
| 0° | 1.00 G | 1.000 × |
| 30° | 1.155 G | 1.075 × |
| 45° | 1.414 G | 1.189 × |
| 60° | 2.00 G | 1.414 × |
Example
If an airplane has a 1-G stall speed of 50 knots in a particular configuration, the theoretical stall speed at 2 G is:
That does not mean the airplane “stalls at 70.7 knots whenever it is banked 60°.” It means that approximately 70.7 knots would be required to avoid reaching the same critical angle of attack while sustaining 2 G under the stated assumptions.
Bank angle is not the fundamental variable
The aerodynamic quantity that changes stall speed is load factor, not bank angle by itself. Bank angle is useful because a coordinated level turn establishes a predictable relationship between bank and load factor. In a descending turn, climbing turn, skid, slip, pull-up, or abrupt maneuver, the load factor may be different from the simple level-turn value.
Accelerated stalls can occur at high airspeed
A pilot can exceed critical angle of attack at an airspeed well above the published 1-G stall speed by increasing load factor rapidly. This is why the FAA emphasizes that a stall can occur at any airspeed and attitude if critical angle of attack is exceeded. Steep turns, abrupt pull-ups, overshooting base-to-final corrections, and poorly executed recoveries can all produce accelerated stalls.
Do not misuse maneuvering speed
Maneuvering speed is often oversimplified as a speed below which “you cannot hurt the airplane.” That is not an accurate interpretation. The FAA notes that maneuvering-speed protection does not extend to multiple full control inputs, repeated inputs, or simultaneous full inputs in more than one axis. The applicable VA or VO and the manufacturer's limitations remain controlling.
Technical basis
This explanation follows the FAA Airplane Flying Handbook discussion of angle of attack and accelerated stalls and the FAA Pilot's Handbook of Aeronautical Knowledge discussion of load factor, stall speed, and maneuvering limitations. See the current Airplane Flying Handbook and Pilot's Handbook of Aeronautical Knowledge.