Say a lot of prayers... especially if checking from / to JFK.
If it measures up to dimensions and weight (50lbs / 62" total of all three measurements, domestic,) you should be able to check it as one of your two bags allocated. But I'd seriously
get it on a insurance policy floater, or get additional declared value insurance from the airline (which may be impossible if they stick to what they say below.)
AA.com's
Baggage Allowance page says:
"
Musical Instruments
Small musical instruments may be carried on-board the aircraft providing they meet existing carry-on size requirements and fit in the overhead bin or under the seat in front of you. Case dimensions may not exceed 45 linear inches (width+length+height). The instrument is considered the passenger's one allowed carry-on bag. A personal item is allowed in addition to the instrument. See Carry-On Allowance for more information.
If an instrument is too large to fit in the carry-on baggage space, an additional seat may be purchased. In this case, an instrument must travel in a window, bulkhead seat, with the customer in the adjoining seat. Due to their size Bass Fiddles are not accepted in the coach cabin and are only accepted on certain aircraft types, please contact an American Airlines representative at 1-800-433-7300.
Instruments may also be transported as checked baggage, however, due to their fragile nature AA does not accept liability for damages and has limited liability for loss."
Anyone recall who the musician was who flew twice monthly to / from JFK - CDG on Concorde with one seat for himself, one for his viola? I remember the FA telling me the story, I can't recall whi it was.