Complex sentence: In 1962 the U.S. Post Office Department granted San Francisco and Oakland Helicopter Airlines airmail contract number AM-103, allowing it to transport U.S. Mail until 1976.
Split into simpler sentences: In 1962 the U.S. Post Office Department granted San Francisco and Oakland Helicopter Airlines airmail contract number AM-103. The contract allowed the airline to transport U.S. Mail until 1976.