Lemurian, Sully's successful actions were not solely the result of a disciplined mind (though I agree that was key) but also the outcome of he and his copilot being experienced pilots.
I think "instincts" is being used to apply to both understanding, practice, and experience in flying. Sort of like the way an experienced golfer selects a particular chip or pitch shot in the region near the green. Without a lot of experience and practice of what would or would not work, the choice may not fit the situation of trying to get the ball into, or near, the hole.