Especially relevant if the players decide to pick up a hangar expansion bay. Do they just spend their carrier's build points to buy the fighters and treat them as equal to the carrier's tier?
Balance-wise, that seems like a reasonable way to run it.
Then again, I don't think the ship examples in the CRB with hangars to carry fighters with are calculated that way. Hrmm...
I guess an alternative (for players) would be to make the fighters you carry around "free" BP-wise, but require them to be no greater than, say, the mother ship's tier/8, or something?...
Or perhaps make the fighters you carry around free BP-wise, but make PCs pay for them with credits, with a credit cost of something like BP X 1000?
Some players want to be fighter pilots.
I would run it as all ships are drawn from the same BP pool, and treat them as equal tier. That way, if a player wants to be a fighter pilot, he/she doesn't get blasted out of the sky due to being so low tier compared to the opponents.
Though I think making them low BP (because they're sharing with the main ship) but high tier makes them strictly less effective (and more likely to be blown out of the sky) than making them low BP and low tier, since being higher tier just makes crew actions in them less likely to succeed...
So if we're going the sharing BP route, I think allocating total BP according to APL, and then assigning individual ships tiers according to their individual BPs, is probably the best way to go.
You would need a fairly large number of players for the PCs to form both the bridge crew of a carrier and the pilots of a squadron of fighters, so the first decision to make is which you are focusing on. If your party is of high enough level to have a carrier as the party ship and you roleplayed them as moving up through the ranks of a military organization, you can give them the fighters for free but handwave any actions that involve them as they probably are of much lower tier than the main ship.
On the other hand, you could get some interesting results if you decide that the party members start out as a squadron of fighter pilots on a carrier. In that case, you would focus on the battles that involve the fighters only as the carrier would probably overwhelm anything that would challenge but not outclass the fighters.
If you are starting them out at 1st level, you should let them know what you are doing with the campaign since they will all require certain skills to be effective. At low levels, you could split up tiers rather than build points among the players and let them each design their own fighter craft (so, for example, a party of 4 PCs would each have a tier 1/4 fighter initially). As they gain levels, there would eventually come a point where divvying up build points rather than tiers is more to their advantage.