The DC-10 is not the cargo version of the MD-11. The DC-10 was built first as a fuel plane to refuel military planes inflight. It became a commercial airplane in the early 70's. In the early 90's this plane after a $4 billion upgrade program was built as the MD-11 with many new features, a more fuel efficient wing etc. American will retire all of these by next year. They are all being sold to FEDEX for cargo conversion.