>>From what I understand (and correct me if I am wrong,) if a pilot at Delta was unhappy and decided to go to United, he/she would have to start at the very bottom of the seniority list. Is this a union rule?<<
It is like any company people who have been there longer get first pick. It is unique to the airline enviroment because it has such a great impact not only on pay but on your quality of life.
>>Also, with this in effect, it seems as if pilots are a dying breed - a group who seeks to stay with the same employer for a long, long time. In other words, how do you choose which airline for whom to work? <<
You really do not have a choice, when you have competitive times, you send out a resume to everyone, and who ever asks you to come and work for them first you go with them. If you start getting picking (i.e. want to fly out of LAX) you rapidly decrease your chances of becoming a pilot.
>>If you had an offer by a smaller carrier, would you jump at the opportunity?<<
If it is a regional you pretty much have to fly for them before the majors (unless you are military). But really as I said before you normally take what who you hear back from first.
>>Or would it be wise to "hold out" for a job from a major carrier, where there is more opportunity for advancement and less liklihood (one would think) of the airline failing?<<
Remember Pan Am back in the day they where classed as the most secure airline. Any airline can go gear up, so you still take pretty much what you get offered.
>>When an airline "goes under," such as Eastern in 1991, what happens to the pilots? Do they go from being high-ranking pilots at Eastern to being bottom-of-the-ladder pilots for other airlines?<<
A friend of mine lost his job with a carrier he was a very Senior Captain with them, when they went gear up, he found himself a very junior FO with AWA make 1/4 of his old salary guys half his age being his cpatain, ect. So yes they are at the bottom of the ladder.
Hope this helped!