different types of operations that a 121 air carrier can do. the same for a 135 air carrier, whatbis the differences between these different types of operations. the various different operations for each type of air carrier (121 or 135), on these types of operations and find and research a U.S. air carrier that is a 121 air carrier and 135 air carrier. two different air carriers. The companies need to be currently in operation and based in the US. the operations of the two air carriers . Where are they based?