American Airlines (AAL) will cease to be a member of the S&P 500 from Sept. 23. After exiting the coveted index, the airline become part of the S&P MidCap 400 index. The change is part of the S&P 500 index’s quarterly adjustment process and reflects AAL’s overall loss of market capitalization over time. AAL's market capitalization, as of Sept. 16, 2024, was $7.1 billion, down drastically from around$37 billion in December 2014. Post Sept. 23, only three airline stocks will remain in the S&P 500 index — Del ...