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Normally one would expect that if the pitch angle is zero, that is the aircraft is level on the artificial horizon, how would the wing present itself to the relative wind at such high angle that it exceeds the critical AOA.?

user2927392
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    What about descending vertically with the fuselage horizontal? Pitch angle = 0°, AoA = 90°. Descending vertically will obviously be in a stall condition. – mins Feb 29 '16 at 07:48
  • But doesn't the vertical dive still provide lift in the horizontal direction (when wings push the aircraft along horizontally, parallel to the ground)?I thought pointing the nose down straight does not make aircraft go straight down. – user2927392 Feb 29 '16 at 08:24
  • In this case, the lift of the wings will make the aircraft going a bit rearwards while going down, due to the small angle of the wings named c on this image (incidence angle), but the wings will be stalled anyway. You need to have a small pitch down angle to really have no thrust and fall vertically (well the aircraft will not stay in this position for a long time). – mins Feb 29 '16 at 08:35
  • The suggested duplicate is worded in the opposite way, but the explanation is the same: pitch and angle of attack are two different, only loosely related quantities. – Jan Hudec Feb 29 '16 at 10:07
  • @user2927392: He's not describing a dive (nose pointed down) but rather falling-out-of-the-sky: the aircraft is falling but the nose is pointed towards the horizon. Imagine a child dropping a toy plane instead of throwing it. While that scenario sounds stupidly ridiculous something like it can happen in a flat spin. – slebetman Feb 29 '16 at 10:19
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    That's one of the factors in the crash of QZ8501. They were confused about the stall warning while the plane was wings level. They weren't accounting for the effect of sink rate on the AOA. – TomMcW Mar 01 '16 at 03:38

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