Never give notice you are, or might be, leaving until you are CERTAIN you are leaving, ie. have an accepted job offer.
Never.
Did I mention never?
Counting chickens before they hatch is bad juju, and trying to 'do the right thing' for your employer could lead to them replacing you before you are ready to leave - if you even end up having the choice.
And yes, I am a former CP of a small 2 pilot/2 aircraft Part 91 flight department who gave my boss six weeks notice that I was leaving.