Take a little of Sailboat's advice. I did, and it's helping!
My YNA Sammy suddenly became downright vicious to me (his sole "chosen" human), about 2 1/2 years ago, possibly because an African Grey came into the flock, and we think Sammy thought his place as the alpha bird was threatened.
The advice I've been following has been to sit beside his cage, and talk to him. Just talk, nothing else - no attempts to touch, no prolonged eye contact (could be taken as a challenge), just...talk.
After just a few sessions, he started to calm down & tolerate my presence again. It's a LONG, SLOW process to regain the trust. Sammy was in 100%, full-on attack mode toward me up until I started doing the talking thing - flying at my face, going for my eyes with beak & talons, and NOT backing down.
I've been at it a couple of months, and now he'll even let me tweak his tail from time to time and (very occasionally) give him a neck scritch, without attacking me.
I've also switched from Harrisons pellets due to the high soy content which, some experts apparently believe, can cause huge hormone swings in Amazons, leading to uncontrolled aggression. It seems that soy (a bulk "commodity" product, like coffee beans) can contain toxic substances, depending on where & when a particular crop is grown...and there's simply no way of knowing where the soy in your latest batch of bird pellets originated. It's probably fine...or, maybe it's toxic. You won't know until you have problems.
I discussed the Harrison's issue with my avian specialist vet (and Harrison's is the brand they carry), and he was surprised by this information...but he thought it might well be true. He plans to do some research and, in the meantime, he suggested switching to another high-quality, soy-free pellet brand. Currently, we're using Brown's "Tropical Carnival"...not because of its bright colors or packaging designed to attract bird owners rather than birds, but because of its content. We showed the content list to our avian vet, and he agreed it seems excellent.
