King using the phrase "flight's ground crew" refers to the people who have sacrificed a lot to make the freedom movement take flight. They are the people who have given their all but are not recognized for their sacrifices. These are the people who worked and fought for what is right and just regardless if they are credited for their contributions. Their reward is to make their dream come into fruition.
The answer you are looking for is The people who have worked hard to make the Civil Rights movement happen but will never be given an award.
In this excerpt from Martin Luther King’s Novel Prize acceptance speech:
<em>“Every time I take a flight, I am always mindful of the many people who make a successful journey possible the known pilots and the unknown ground crew… You honour the ground crew without whose labour and sacrifices the jet flights to freedom could never have left the earth.”</em>
Mr King compares the people who have worked hard to make the Civil Rights movement happen but will never be given an award, to a flight's ground crew in this metaphor.
