No, you do not strictly need to be flying on American Airlines to access the Admirals Club, but you must be flying on a "qualified" flight to enter. According to current policy, you must have a boarding pass for "same-day travel" on any flight operated by American Airlines, an airline in the oneworld® alliance (such as British Airways, Qantas, or Qatar Airways), or an American-marketed flight. This means if you have an annual Admirals Club membership or an executive credit card (like the Citi® / AAdvantage® Executive World Elite Mastercard®), you can enter the lounge while flying on a partner airline like Alaska Airlines or Japan Airlines. However, you generally cannot access the club if you are flying on a completely unrelated carrier, such as United, Delta, or Southwest. Additionally, those who purchase a "One-Day Pass" for the lounge are subject to the same requirement: you must be flying with American or its partners that day. There are specific exceptions for certain military personnel and high-tier elite status members on international itineraries, but the core rule is that you must be part of the "oneworld family" for that day's travel.