Continuity mistake: Burt Lancaster is sitting in his car at the end, and he asks the tower if he can listen to the radio traffic for the incoming plane that's landing. The tower replies "Sure, it's on frequency 117.1". Burt then tunes the dial on his receiver to 171, not 117. 170 is blatantly written under the dial in bold type.
Continuity mistake: When arguing about the expansion of the airport with Ackerman, Mel steps behind a display model of the airport layout. We see him standing in one position for several seconds, but in the next shot his arms are positioned completely differently, and he is standing in a slightly different spot. (00:45:15)
Answer: You are right. I have seen the film 100 times and never questioned that. There is no reason for only some of the crew to be on the plane, but it was needed for the scene to work.