I have a question for you guys about type ratings.

How does it work when you go from a F/O to Capt. Do you have to stay on the same type aircraft or can you move to another? Do you always start on smaller aircraft? (Meaning mainline) If you are a Captain on a 737 can you switch (bid I guess?) to a larger plane and maintain the rank? Is the F/O bidding the same?

Sorry for the random questions. I'm a full time firefighter in dirty Jersey. Most my family lives in LA so I fly out there a lot. I have always wanted to ask. I also work part time on the ramp. The only thing I really ask is "wings and tail, or the whole aircraft?"