Involuntary actions by the airline, such as flight cancellations, or significant schedule changes, generally qualify you for a full refund. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) Other qualifying reasons include the death of a passenger or traveling companion, certain military orders, and specific health-related issues. 

Airline-initiated issues

Federal regulations entitle you to a full refund if American Airlines (AA) cancels or significantly alters your flight, and you decide not to travel. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) 

• Cancelled flight: If AA cancels your flight, you are entitled to a full refund to your original payment method.
• Significant schedule change: If the airline changes the flight itinerary by a significant amount of time (for example, three or more hours for a domestic flight or four or more for international), you can opt for a refund. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) 
• Delay causing missed connection: If an AA flight delay causes you to miss a connection and AA cannot get you a comparable seat on a rebooked flight, you can get a refund for the unused portions of your ticket.
• Involuntary downgrade: You are entitled to a refund for the difference in fare if you are involuntarily moved to a lower class of service, such as from First Class to Economy. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) 
• Involuntary denied boarding: If you are "bumped" from an oversold flight and do not accept alternative arrangements, you can request an involuntary refund for that flight.