Originally Posted by
grossole
For ATP PIC requirements, you may substitue 1/2 of your SIC time as PIC.
Not for a US ATP. You need 250 hours of real PIC, period.
For an ICAO ATP, you need 1200 hours PIC but you can SUBSTITUE two hours of 121 SIC for one hour of PIC (you still need some amount of real PIC). This means a low-timer will need 2500+ 121 SIC to qualify for ICAO ATP privileges.
The ICAO ATP is not required for domestic US flying, but most jet regionals go to canada and/or mexico so most require ICAO times to upgrade. Most turboprop-only operators should not require this.