Originally Posted by aa.com

AA to/from AA or a oneworld® Carrier

If a customer is holding separate tickets on AA or another oneworld carrier, customers holding separate tickets where travel is on oneworld airlines should be treated as through ticketed passengers. In the event of a disruption on the originating ticket, the carrier responsible for the disruption will be required to reroute the customer to their final destination. The ticket stock of the second ticket must be of a oneworld carrier, eligible under the Endorsement Waiver Agreement. You may contact AA Reservations 1-800-433-7300 (U.S. and Canada) or outside the U.S. and Canada, reference Worldwide Reservations Numbers for additional information if the separate ticket is for travel on a oneworld carrier.