Ok Dakota, your turn,
Repeat after me, “SENIORITY IS EVERYTHING”. So every now again due to changes in operation (new airplanes coming in, old going out, new destinations, retirements etc) the airlines will have open positions on various airplanes, bases, seats (CA and FO) so they will open a “Vacancy Bid”. ALL pilots participate and will “bid” for what they want and you can (and should) bid for anything and everything. For example you could be the most junior pilot at the company and you can bid 787 CA. Now what you get is based on… you got it, SENIORITY. If you’re senior enough to hold that slot, seat, airplane, base whatever you get it, if not you don’t. So using your example you’re a 737 FO and want to go 777. There’s some shuffling and there’s 1 777 FO slot. You bid it. If no one senior to you wants it, congrats you’re a 777 FO but if someone else SENIOR to you does you don’t. For a real world example we just had a vacancy bid 2 months ago and I bid 717 CA. Now if you look at the numbers I really shouldn’t be anywhere near holding CA but most of the pilots who were senior to me either didn’t want to leave the A330 OR didn’t believe they could hold it so I got the 1 open slot. Afterwards a bunch of pilots senior to me were annoyed they didn’t get it. I asked “did you bid it?”. They all said they didn’t think they could hold it and didn’t. Oh well? Bottomline ALWAYS bid what you want NOT what you think you can hold. Make sense?