Narrative:

I was sic on an IFR flight departing from ZZZ. The PIC asked me to pick up our clearance prior to our departure. I received our clearance from ZZZ clearance delivery frequency. Our clearance route was 'via radar vectors then as filed.' the PIC determined that we would have to fly the published odp (obstacle departure procedure) for runway xxl at ZZZ. He insisted that since we were not given a departure procedure; the odp was mandatory.immediately prior to receiving our take off clearance; tower gave us a new departure frequency as well as departure instructions. I read the instructions back to tower and accepted our take off clearance. Our instructions were 'on departure turn right heading 270 climb and maintain 3;000 cleared for takeoff runway xxl.' shortly after rotation and during our initial climb out; the PIC began a left turn to heading 150 to follow the odp. I challenged the PIC by saying 'I believe it's a right turn to heading 270'. The PIC responded to me with 'we're following the odp.' approximately 2 seconds later; tower instructed us 'I need you to make a right turn; that's a right turn to 270 immediately.' the PIC assumed radio communications from me at that time and responded to tower with 'we're following the odp.' the PIC continued the left turn to heading 150 after being instructed by tower to turn right heading 270. Tower then instructed another aircraft to make a left turn heading 090 immediately. The PIC finally listened to tower's instructions and began the right turn to heading 270 after several seconds of defiance. Tower was professional at all times and politely asserted that clarification of clearance needs to be made for future reference.

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Original NASA ASRS Text

Title: Air Taxi First Officer reported Captain flew Obstacle Departure Procedure instead of assigned departure resulting in an airborne conflict.

Narrative: I was SIC on an IFR flight departing from ZZZ. The PIC asked me to pick up our clearance prior to our departure. I received our clearance from ZZZ Clearance Delivery frequency. Our clearance route was 'Via radar vectors then as filed.' The PIC determined that we would have to fly the published ODP (Obstacle Departure Procedure) for runway XXL at ZZZ. He insisted that since we were not given a departure procedure; the ODP was mandatory.Immediately prior to receiving our take off clearance; Tower gave us a new departure frequency as well as departure instructions. I read the instructions back to Tower and accepted our take off clearance. Our instructions were 'On departure turn right heading 270 climb and maintain 3;000 cleared for takeoff runway XXL.' Shortly after rotation and during our initial climb out; the PIC began a left turn to heading 150 to follow the ODP. I challenged the PIC by saying 'I believe it's a right turn to heading 270'. The PIC responded to me with 'We're following the ODP.' Approximately 2 seconds later; tower instructed us 'I need you to make a right turn; that's a right turn to 270 immediately.' The PIC assumed radio communications from me at that time and responded to tower with 'We're following the ODP.' The PIC continued the left turn to heading 150 after being instructed by tower to turn right heading 270. Tower then instructed another aircraft to make a left turn heading 090 immediately. The PIC finally listened to tower's instructions and began the right turn to heading 270 after several seconds of defiance. Tower was professional at all times and politely asserted that clarification of clearance needs to be made for future reference.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.