Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Confusion
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
Our flight plan took us from the Montrose airport to the Blue Mesa VOR with no departure procedure.  Because the company prohibits our aircraft from flying the obvious Blue Mesa departure; the captain elected to have us use the Montrose 2 obstacle departure procedure. I saw no safety issue with this decision so we briefed our plan together.  We were cleared as filed by ATC so after the captain loaded the flight plan; I pulled out the paperwork to verify our route. Everything was entered correctly including the first waypoint after the MTJ VOR; HBU (Blue Mesa).  We departed Montrose and I hand flew following FMS guidance to make the left turn to H250 followed by an eventual right teardrop turn back to the MTJ VOR. During the turn back to the VOR the captain verbalized he was going to hit direct MTJ. I was not sure then; nor am I sure now why he wanted to do that instead of just continuing on the DP but there was no time to speak up as he was already pushing buttons while communicating. I noted right away that the change would keep us inside of the DP's route so it seemed like a bigger threat to attempt to put the FMS back the way it was instead of just flying present position direct to MTJ. What happened from here isn't entirely clear. Because we both verified the flight plan prior to departure; my only guess is he mashed too many buttons trying to do the direct (It was a bit of a bumpy ride down low) but somehow he changed our flight plan from MTJ - HBU to MTJ followed by whatever waypoint was planned for after HBU. I can't recall now what it was. This new path started us way off course and got ATC's attention as it did put us heading towards traffic. ATC queried us to find out if we were going direct to Blue Mesa while also asking if we showed something different on our flight plan. ATC then gave us a vector back to Blue Mesa in order to ensure traffic separation. The biggest threat was definitely a lack of communication and verification of FMS changes made in flight. I am certain the flight plan was verified because I was more alert than a normal flight because of my unfamiliarity with the area and the terrain. Flying the wrong route after the FMS change. Not knowing the VOR identifiers the way I might in a more familiar area contributed to my lack of catching the problem early enough. Considering how much more alert I was to obstacle threats; I really should have let the autopilot fly sooner so that I was more free to monitor things. Terrain gave me a bit of tunnel vision causing me to miss the flight plan error.
Air Carrier First Officer had planned to fly the Montrose 2 obstacle departure procedure which was loaded in the FMC; but the Captain began altering the procedure during departure resulting in a track deviation and ATC intervention.