Gordy, Sorry if I implied that an ATP is required for all P 135 Ops. It's not, but there are some circumstances where it is:
§135.243 Pilot in command qualifications.
(a) No certificate holder may use a person, nor may any person serve, as pilot in command in passenger-carrying operations—
(1) Of a turbojet airplane, of an airplane having a passenger-seat configuration, excluding each crewmember seat, of 10 seats or more, or of a multiengine airplane in a commuter operation as defined in part 119 of this chapter, unless that person holds an airline transport pilot certificate with appropriate category and class ratings and, if required, an appropriate type rating for that airplane.
(2) Of a helicopter in a scheduled interstate air transportation operation by an air carrier within the 48 contiguous states unless that person holds an airline transport pilot certificate, appropriate type ratings, and an instrument rating.