Can Someone Explain the Title?

Of course, the title is taken from the book. I never knew specifically what author Ernest K. Gann intended, but it seems likely the title vaguely refers to the passengers and crew aboard the plane. I think it just sounds dramatic without necessarily having much to do with the plot or action. Hardly a unique literary device.

It was a popular saying back in the day. It's used on two fronts.

It's used to show that the true courage of certain characters emerged under tremendous strain while they were literally at high altitude. It also indicates that certain characters were humbled and "brought back to earth" because of the events of the film. Some people had very messed up priorities.

It was the title of the book. The beginning of the book spends a little time laying out the mentality of airline pilots, how they have a very inflated sense of self brought about somewhat from the position and the salary and also from the training needed to be completed before they qualify as well as the awesome and awful responsibility involved when all those souls are under your care. The characters are well laid out as to how Sullivan and Dan Roman and the 3rd pilot all fit into this description and how their levels of experience influence their view of this responsiblity and/or their view of how their title influences their salary. (note: in 1953 when the book was written, $1000 a month salary was considered high earnings and something to be envied.) At the end, when all is said and done, the executive goes from thinking that Sullivan deserved to be prosecuted for negligence in his loading of fuel to realizing that he was not there in that seat and that he had been "the high and the mighty" with a huge weight on his shoulders. Sometimes the book answers the questions that the movie leaves vague.