This picture is one of the most frequently viewed from my galleries. I guess it’s because of the relatively steep bank angle, as this is the only thing that makes it different from other pictures.

Because it has been taken in a descending turn, the natural horizon is high and easily visible. Now comes an interesting trick. What do you reckon is the bank angle (for non-pilots, the angle between the plane floor an the natural horizon) ?

If you think “45° or more”, read what follows. Otherwise, read it anyway, it’s interesting. On the picture below, I stretched the artificial horizon. Not only you can see that it matches the natural horizon quite well, but it is also possible to read the bank angle value accurately.

The large ticks on the horizon are each 30 degrees, so this picture confirms a bank of approximately 20 degrees. One can argue about parallax because the photo has been taken from the right-hand seat, but this will not make for 15 degrees. There are two factors that make this image misleading to the human perception.

The horizon seems to split the picture in two, being parallel to a line going from the top-right to the bottom-left corners. This suggests a 45 degrees line, but as the picture is not a square, it’s not the case. Another factor possibly disturbing the bank angle perception is the top of the dashboard. One tend to use it as a natural horizontal reference, but if you compare it to the top of the picture, you’ll see that the photographer did not held the camera parallel to the plane axis.

Moreover, the top of the dashboard is not flat, but slightly curved. The DA40 with G1000 is also a perfect example of curvy dashboard. It always somehow disturbed me when flying IFR, because it creates the “feeling” of bank. A large part of IFR training is learning to trust the instruments, and disregard wrong physiological perception.

What lessons can we draw from that ? The way our brain combines and interprets images with other sources of orientation can lead to wrong perception. Human performance chapter one, paragraph one – but always worth a good refresh. Trust the instruments, not your perception, and build a good mental awareness… so as to detect instrument failures

Want to read more about spatial disorientation ? Click here to see that it can even happen when flying VMC.