Originally Posted by
Smythe
Actually, yes, you can, and the 767 tanker does compare the AoA vane with the gyros.
No, it does not. If you believe that it does, please provide a published reference.
Although you can use the indicated airspeed, groundspeed, pitch angle, and rate of climb to try to estimate AoA, the results are subject to the cumulative errors associated with each individual measurement. Additionally, as described in the article, the computed AoA diverges from the actual AoA as you approach stall, which is exactly where you need accurate AoA the most. The linked article chalks this up to unmodeled forces and moments in their algorithm, meaning their method can only ever be an estimation.
One of the most critical problems with an AoA computation algorithm is that it can only tell you what your AoA WAS, based on previous airdata measurements. Additionally, an unchanging atmosphere is assumed. They cannot tell if the aircraft is encountering an updraft or a downdraft, or is descending through a shear between air masses with two different wind directions, both of which will change the actual AoA. The derived AoA systems are extremely laggy compared to direct measuring devices. I have flown behind the Aspen "derived AoA" described in the article, and I do not plan on spending the extra $2000 on that option when I do my own Aspen installation later this year. I am considering the Alpha Systems pressure-based direct measure AOA probe and heads-up display. I've flown behind that in a friend's plane, and found it to be responsive, and the HUD was actually useful compared the Aspen indicator that is way outside of your VMC scan. Lots of good videos of that Alpha Systems AoA in action if you search YouTube for "Backcountry 182"