Question: First there's a scene showing the "Golden Argosy" flight crew taking a mini-bus out to the plane (which, I assume, is already at the gate). The next scene shows Vernin Demerest and Gwen Meighen alone on the plane talking about her being pregnant, etc. Later in that same scene we see the rest of the crew getting onto the plane while Demerest and Meighen are all-of-a-sudden pretending there's a problem with a light. My question is this: If they all went out to the plane together on the bus where were the rest of the crew while Demerest and Meighen were talking on the plane? Wouldn't the whole crew have arrived together and got onto the plane together?
Answer: For that matter, why would the crew take a bus to a plane that's already at the gate? Wouldn't they just board via the jetbridge?
Now, yes, they go through security with the passengers. Prior to 2001, crew on my airline often took a private bus from the sign-on building to the aircraft.
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.