During the mid-20th century, planes overtook trains as America’s most popular mode of travel. And as businessmen dominated commuter flights, airlines responded by using sex as a marketing tool. Airlines began imposing height, weight and age requirements for their flight crews, and uniforms took a turn for the risqué. Women who got married or pregnant were fired, and those who approached their early thirties were encouraged to retire, or transferred to the ground crew. But when President Johnson signed the Civil Rights Act of 1964 into law, everything changed.