Originally Posted by
TomMM
And what about a situation where the FO needs to take command of the aircraft and perform to ATP standards?
A FO under previous rule, which permitted a FO to have a CPL (250 hours), still meant the pilot would undergo training with the airline in systems and maneuvers, and would serve in that capacity (not an aircraft commander) until reaching the 1,500h threshold for an ATP, which did not change. Now, in order to serve as a FO for a US Part 121 carrier, an ATP is required. So it's not an issue of type- or operator-specific training, but rather overall experience.
The rule is controversial, but as a general matter it is premised on the theory that more hours = more experience = better/safer pilot. Importantly, it's not to say that 1500 hours = safe pilot, or 1500 hours = well-trained pilot, but there is no doubt that an ATP must demonstrate a higher degree of proficiency to earn the ticket.