"Flight crew berths" are crew quarters space for the crews of parasites, like fighters and dropships.
To decide how many flight crew berths you need, you first have to design your parasites, and decide how many your main craft will carry.
For example, if I'm building a carrier, I first decide how many fighters it'll carry. Lets say 10 for this example. Then I design the fighters. Once they're designed, I know they take 3 crew per fighter. Meaning I need at least 30 flight crew berths on the carrier.
It can be a good idea to add extras to allow the carrier to be used with other fighters that have not been designed yet and may require more crew, or to allow the carrier to pick up survivors from life pods without overcrowding.
