Not at all Ryan, it’s actually a great question.
In order to move or transition to any “seat” or position (whether we’re talking FO to Capt, or different aircraft) there are basically 3 requirements. A) The company must post a “Vacancy or System bid” (they come out based on need due to any number of reasons but generally pilots leaving, retiring or new aircraft, *On a side note when it comes to bases many airlines have separate Base bids to allow pilots to move or trade bases. Those come out more frequently than Vacancy bids), B) there has to be a “vacancy” (open slot) in that bid and, C) your “seniority” must be able to “hold it”. So let’s use me for example here at Hawaiian. Most important things to keep in mind is you can’t just simply move whenever you like. When I was first hired I was assigned to the 717. Now whenever you get assigned OR swap aircraft there’s usually a “seat lock” (2-3 yrs) which prevents you from moving again (training is expensive and they can’t just have pilots hopping from aircraft to aircraft). Now after 2 years my lock expired but I wanted to transition to the Airbus so I bid Airbus FO. Now there were only 6 open slots and they get awarded to those who bid those Airbus FO slots based on their seniority. If there were 6 guys senior to me (which there was) I don’t get to move. EVEN THOUGH there were Airbus FOs junior to me on the aircraft due to their initial assignments, you cannot push another pilot out, there MUST be an open slot. The next bid came out and again I bid Airbus FO, there was a slot and my seniority held it so voila! I got it. Now I’m waiting to upgrade so again it’s a question of waiting for a bid, a slot and my seniority to hold it. Now the exception to all this is if a pilot gets “displaced” they can then displace another pilot. For example (again using Hawaiian) we’re phasing out our 767s so the most junior 767 pilots are losing their positions. They then can displace ANY pilot in any seat or aircraft who’s junior to then and that pilot can in turn displace another.