I'm thinking about something different.
My thoughts:
Segment
A segment is a line in the itinerary that represents a flight item, along with its seat number. I mean, not the full list of available flights (Flight class), just a mapping between the itinerary and its items (segments). Each segment is then related to one flight, beacuse each segment are the flight details for an entry in the Itinerary (Although a flight might be related to many segments, one per seat in the plane).
Flight
Flight classes are the available list of flights, it's origins, destinations, flight number and timing. Each flight is related to an equipment, though an equipment is related to many flights (another potential incoherence of the BDM and/or my interpretation).
Equipment & Seats
Equipment are planes and seat are its seats. That's obvious, but the point is that both of these elements won't change unless the company buys new planes.
This is my interpretation. For example, if a customer bought a Pto. Rico -> New York route, and it has a connection in Miami it would be separated in two itinerary items (segments). The delicate thing is that under this approach, the flight number could not be the PK of a potential flight table, the key should be composed of the flight number along with its origin and destination.
Is this ok? or is it wild?
Best regards
XM