A variation of this is where two airports serve, or served, the same city. We expect that with very large cities like New York, Chicago, and Los Angeles, but in looking at a USAir schedule from the 1970s, I noticed that US had service in the same schedule to AIY (Bader Field/Atlantic City Municipal) and ACY (Atlantic City International). In the 1979 schedule, Southern Jersey Airways as Allegheny Commuter went from AIY to PHL while mainline service went to PIT. This apparently lasted until 1990.