The correct answer is "the airlines ground crew".
In his Nobel Prize acceptance speech, Martin Luther King uses a metaphor in order to resemble all of the "unknown" heroes of the Civil Rights movement in the form of the ground crew who makes it possible for a jet to take off. The ground crew is not the visible part of the journey, nor will get the appreciation the Air Crew or the pilot might get, but they are equally as important in order to achieve a successful air trip. Just as all of the people who made efforts throughout the country's history to achieve equality of rights among all citizens of the United States.
