# Can the pitch be very different from the angle of attack?

Audrius Meškauskas
• Can the pitch be very different from the angle of attack? Audrius Meškauskas

How much the pitch (horizontal orientation) can differ from the angle of attack? I am trying to understand the claim that "angle of attack indicator was unfortunately not available", contributing to problems during Air France Flight 447. Attitude indicator most likely was available?

• It can be. Remember that the angle of attack is the angle between the chord line of the airfoil and the relative wind. Imagine if the plane is level with the horizon with zero airpseed. It will fall straight down, putting the angle of attack close to 90 degrees with the pitch close to zero.

That said, during normal flight it's not likely that pitch and angle of attack will be excessively different. But honestly the two aren't closely related: You can exceed the critical angle of attack and stall at any pitch, bank, or yaw angle.

• The angle of attack is the angle between the wing (wing chord to be precise) and the direction of travel (undisturbed airflow). The angle of pitch is the angle between the main body axis and the horizon. The difference can theoretically be any angle, but during normal flight it will be limited to about 15 degrees.

The reason that the angle of attack indicator was inoperative was due to low airspeed. Below 60 knot IAS the indication is unreliable and therefore the indicator is inhibited. This also inhibits the stall warning. This lead to the confusing situation that lowering the nose to correct the stall increased the airspeed beyond 60 knots, thereby reactivating the stall warning.

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• How much the pitch (horizontal orientation) can differ from the angle of attack? I am trying to understand the claim that "angle of attack indicator was unfortunately not available", contributing to problems during Air France Flight 447. Attitude indicator most likely was available?

• Here is a \$C_L\$ / \$AoA\$ curve that I took from Wikipedia. The better textbooks say that a stall is that condition in which a further increase in angle of attack will result in a reduction of lift. The point at which that transition happens is known as the critical angle of attack. Theoretically, sustained flight is possible at angles beyond the critical angle of attack - take a look at the chart. If the airplane can sustain level flight at point \$A\$, it can sustain level flight at point \$B\$. Is there a practical way that I can demonstrate sustained flight on the backside of the lift

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