For many decades, AA was a very stiff, formal organization where men had to come to the office in suits and women had to wear heels, hose, and dresses.
The same applied even when flying "non-rev", or non-revenue (for free). Imagine being the only person wearing a suit or dress on a flight to Hawaii!
The atmosphere is definitely more relaxed now. Jeans are acceptable to wear on Fridays to the office. We just relaxed our dress code when flying non rev.
What still remains is a very hierarchical structure which promotes from within, before looking for outside talent. It is very, very difficult to come into organization as an experienced hire (Sr. Analyst or Manager), because the opportunities are first given to internal employees. The bottom positions are easier to get into, but of course the turnover rate is enormous and it can take several years to built up enough experience to move into the higher ranks.
The one exception for experienced hires, if you are lucky enough to be selected for it, is the MBA rotational program. This program is designed to rotate one through various departments at AA (e.g. Finance, Mkting, Ops), in order to groom them for a VP or even CXO position. However, AA looks for graduates of certain B-schools (just having an MBA does not guarantee acceptance), and the selection process is very, very tough.