I was reading an article in Aviation Week that Mesa Airlines is selling back Beech 1900D's to Raytheon. Supposedly, now that Mesa is a part 121 carrier it is getting too expensive to operate the Beechs. The move the 121 was due to the fact that they are now a large RJ operator for USAirways and America West. So what operational differences and costs would be greater to operate Beech 1900s on part 121 vs. part 135?
Thanks ahead of time.