On the cards:
I like Invention. Arguably, it'sstronger than the other starting Travellers, but that okay, since when it's strong, you want to keep it,and as a $2 cost, it's not overpowered. It's actually worse than Squire, the same way Page/Peasant are worse than Pawn.
Draft might be too strong. Comparisons are Remodel (gets a better card, but only one of them) and Trader (also can transform an Estate into 2 Silvers, but is less flexible). Both of these cost $4. And the card is absolutely nuts with $7 costs on the board. If it turns out to be too strong, I suggest putting "two differently named cards" in there. That at least gets rid of the double Province problem.
Construction is basically a nonterminal Moneylender? Thus already better than a $4 cost, but that's okay. By the time you get this, it's probably rather bad. Well, if you're going moneyless, it's strong, but not in a broken way. This is probably okay.
Test Flight I don't get. It's strictly worse than Lab, and you have to wait that long to get it? I think each stage in the Traveller chain should at least have some scenario where you'd rather keep the card, but I don't see myself ever keeping Test Flight.
Flying Machine - it's situational, but obviously good with the right board (KC/Bridge?). I like that it gives you megaturn options on boards that usually lack that potential. It has some similarities to Madman megaturns, and man these are cool.
Overall, I like most of the cards. I also like Flying Machine and don't think it's too weak. But one problem I see is that Flying Machine is probably best on decks that lack trashing or drawing - and two of the cards in the chain provide trashing. So this may end up a self-counter in a way. I think you might want some other effects there, preferably some that go well with big hands, because I think Flying Machine could use a little self-combo. Maybe keep Draft because it's fun, but I would switch construction by something else.