Mayomick, I now understand what you are saying, although my first reaction was the same as that of Suegorgeous. However I believe you are mistaken in thinking the construction you quote is a contraction of "am not I". Do you have actual evidence for this? My reasons for disagreeing are:

Firstly, if this were the case it would be pronounced with a short a, the same as "am".

Secondly, I have never heard anyone pronounce it as "armpt" or seen it written as "amn't". Everyone I know, myself included, says "aren't" and that's how it's usually spelled. I think it's a bit tortuous to infer a silent "m" because you think it should come from "am"

I'm not even sure that "aren't I" is actually grammatically incorrect. The whole "aren't I?", "aren't you?", "isn't he?" construction is a rearrangement of the proper word order - you would say "am I not?", not "am not I?" - but is so universally used that I am more inclined to think of it as the correct construction when used in that particular context. This is only found in colloquial speech, and you wouldn't write it unless you were quoting or reporting speech. Colloquial speech frequently uses different grammatical constructions from written English - indeed, anyone who insists on speaking strictly grammatical English usually sounds a bit prissy.