Following Summer of Hell in 2000, then CEO Jim Goodwin aired an Apology. IMO, his rank incompetence was shown right on his face. You can clearly tell that he was reading past the camera to the script behind it, and not looking directly into his audience (nor speaking from his heart, take your pick). Although I never doubted the sincerity behind his apology, he came across looking as if he were just sucker-punched, and that he had no clue what to do next.

In the wake of 9/11, UA's campaign theme became "We Are United." IIRC, one of the first ads was "Passion." Those were somber and sad ads. I'm not sure how effective they were, because 9-11 was an extraordinary event and I doubt anything at the time could have eased the public's anxiety. (Dennis Fitch, one of the heroes of the SUX DC10 crash, appeared at 0:14.)

UA went Ch.11 in 2002. Commercials through 2003 included fare sales and several other forgettable spots. (no links)

In 2004 UA adopted "It's Time To Fly," and took a risk by using whimsical cartoons instead of photo-realistic imagery. The campaign focused on restoring the confidence of business travelers, as well as putting some fun and excitement to the flying experience again. IMO, this was THE BEST marketing campaign among all U.S. carriers in recent memory. My favorite ads were "A Life," "The Meeting," and "Dragon," which IMO is destined to be a classic of all-time.