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I was looking at this video of the AF447 crash simulation and at about 4:45 the angle of attack diagram shows a few things I don't understand (frame above).

I get the orientation of the airplane, pointing a few degrees above the horizon, but what does the green line represent in layman's terms? Is that the direction the plane needs to go for the wings to generate lift?

Also, I see the red line has to do with the warning, but how does that play into it as well?

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  • $\begingroup$ Can you clarify if you're asking about the line in the upper-right inset or something else? $\endgroup$
    – BowlOfRed
    Mar 15, 2019 at 21:23

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There are several colored lines. Which one are you asking about? I'm assuming you are referring to the (cyan?) and red lines in the upper right inset.

enter image description here

The cyan line shows the current direction of the airflow. When compared with the orientation of the airplane can show the angle of attack. At this time, the relative wind is coming at a very steep angle to the airplane and the wing is stalled.

Another way to see it is that reversing this arrow shows the direction the airplane is moving through the air. In a no-wind situation, this would also be the direction the plane is moving with respect to the ground.

The red line is at a constant angle with respect to the airplane and shows how low the airflow can go without causing a warning. As it is below this line, the stall warning has sounded.

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    $\begingroup$ Maybe it would be good to add a sidenote that the cyan line shows the opposite of „where the plane goes“ (I assume that for non-aviation folks earth fixed is the more natural frame of reference rather than airplane fixed). $\endgroup$
    – Cpt Reynolds
    Mar 15, 2019 at 21:24
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enter image description here
Adapted from norebbo.com

The green is the same as the cyan in the small window in the top-right corner. It is where the plane is going right now. In cyan the arrow head represents the air hitting the aircraft's belly. In other words, the plane is falling belly first.

The red represents how big an angle is needed to trigger a stall warning; the green/cyan is much bigger. The plane needs an angle smaller than the red (more toward the nose) to not be close to a stall.

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