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My HUD doesn't have an AoA indicator. We have no reference for AoA and don't need it. If you're in a Typhoon or something similar then you do use it.
Consider this. An airliner flying at 250kts at a constant altitude will have a pitch attitude of, say, 5 degrees. An AoA of, say, 10 degrees.
Now you slow down to 150kts an extend a bit of flap. You maintain your constant altitude. Your pitch attitude can be maintained at 5 degrees because you're extending flap.
Now, what is your AoA? Bearing in mind the lift equation which basically states that if you reduce speed you must increase your angle of attack to maintain your altitude.
Your AoA will be more than the 10 degrees required for 250kts. Say 15 degrees for arguments sake.
But, the indications on the HUD of the aircraft pitch and the flight path vector will be the same.