Complex sentence: Fairfax Airport was an airport in Kansas City, Kansas from 1921 until it closed in 1985 that is most famously associated with the construction of most of the B-25 Mitchell bombers.
Split into simpler sentences: Fairfax Airport was an airport in Kansas City, Kansas from 1921 until it closed in 1985. It is most famously associated with the construction of most of the B-25 Mitchell bombers.