I use AA for flights from the continental US to the Caribbean. Most of those flights limit checked bags to 50 lbs and 62 total inches. Bags over 50 lbs but under 70 lbs are charged $100 each. Bags over 62 inches are supposed to be charged $200 each - I've never seen this fee enforced but that might be because I was a serious frequent flyer at the time.
Sporting equipment policies are worth reading closely:
* surfboards/kiteboards/wakeboards/wave-ski go as a regular checked bag if below 50 lbs and 62 dimensional inches (no chance!). If larger but still below 70 lbs and 126 dimensional inches then they cost $150.
* windsurf/kitesurf equipment (yes, this is a separate section from above) costs $150 - but can be two pieces, 70 lbs, and up to 126 dimensional inches.
* A golf bag goes as a checked bag with no extra fee and has the advantage of allowing up to 70 lbs without charge. It doesn't have a quantitative size limitation but says it "it limited to the size of a hard sided golf case".
* boogie/skim/speed board goes as a checked bag with no extra fee - but can't exceed the 50 lb 62 inch limitation. That won't work for your twin tip.
* skis/snowboards go as a checked bag with no extra fee and may be up to 126 dimensional inches. I have travelled to the Caribbean with kites in a duffel as a regular checked bag and taken my twin tip as a "snowboard" in a twin tip bag. Surprisingly, I didn't get many questions. They asked "What's this?" I said, "My snowboard." They said, "OK."
AA policy varies with origin/destination. For details on your location check http://www.aa.com/i18n/travelInformation/baggage/baggageAllowance.jsp
. If you want the details on sporting equipment, make sure to check the appropriate checkboxes.