1982-ish. TWA had a promo where if you flew 5 segments and 5,000 miles, you earned a domestic RT First class ticket. Yes, you read it correctly. I figured out that SAN-LAX-STL-JFK-STL-SAN came in at 5,043 miles. We talked friends into coming with us and had an awesome weekend in NYC. We used our free tickets for Hawaii and they used theirs for Alaska.