Complex sentence: The company first used the Cessna 180 which was later replaced by the larger Cessna 185, later in 1975 the Cessna 206 and 207 were added.
Split into simpler sentences: The company first used the Cessna 180 which was later replaced by the larger Cessna 185. Later, in 1975, the Cessna 206 and 207 were added.