It all goes back to when the 19/29* pax airlines still operated under part 135. They were allowed to fly 1200 (or maybe1500) hours per year. After the FAA initiated its "one level of safety" program and put all scheduled carriers under part 121 except the former 135s were still able to drive their pilots harder. Yep, one level of safety.



*back in the day, 29 pax INTRAstate and 19 pax INTERstate airlines were operated under 135. http://ecfr.gpoaccess.gov/cgi/t/text....6.3.4&idno=14