Look here at what is written in the Pet Store. The Segment, Flight, Equpment classes are somehow similar with Pet Store's catalog classes.
"Catalog entries are modelled as conventional classes. In this application, catalog entries provide an excellent example of when not to use enterprise beans. Catalog entries are simple, tabular data with little or no behavior. They do not need the services enterprise beans provide. For example, because they are read-only, they don�t require concurrent update management or transactions.
Modelling catalog entries as entity beans would create unnecessary overhead.
Modelling them as conventional classes meets all of their requirements in the simplest, most efficient way."
In addition, you can avoid database calls by caching segments, flights, and equipments.