Thank you for contacting Customer Relations.I'm sorry you were not able to check in for your return flight on AA729 from London to Philadelphia on July 27, 2018 being told since your original outbound flight was not used you had been removed from your return flight. Our records indicate that while you did check in online the night before, we do not find that you checked in at the airport on July 27 or that you boarded flight AA736 from Philadelphia to London on July 19, 2018. In fact, it should also be noted that this flight departed with multiple empty seats - there was no denied boarding for any passengers ticketed for this flight.In most instances when a segment of an itinerary is "no-showed," future segments also go unused. Therefore, when customers do not travel on flights for which they have confirmed reservations, we automatically cancel all remaining flight segments. When a customer presents a ticket for "return" travel without having used the "outbound" segment, the ticket is considered void for that trip. In such cases, it is usually necessary to purchase a new one-way ticket at the applicable fare.Compensation associated with EC261/2004 does not apply when a passenger does not travel on an outbound flight as ticketed, causing the return flight to be removed from the reservation. Therefore, there is not any mandated compensation warranted for flight AA736 on this occasion and we must decline compensation and adjustments based on the EC 261/2004 regulation. We appreciate this opportunity to review your claim