Date: 201602
Local time of day: 0601-1200
Location: MTJ.Airport, CO
Flight conditions: VMC
Aircraft: Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class E ZDV
ATC / advisory: TRACON ZDV
Second aircraft: Light Transport
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Airspace Structure
Primary problem: Airspace Structure

Narrative: Cleared by Denver Center for RNAV Z Runway 17 in visual conditions; skies clear. We slowed down to follow other inbound traffic that center called out to us but we did not see. Inbound from BRUUK and before WIDRU a VFR [light transport] entered final in front of us from the west at WIDRU. We were already at final approach speed and were catching up with him. As traffic got closer we felt we were too close to complete the approach and landing behind him and had concerns for climbing over him on a go around since his altitude seemed high for the approach at or near our same altitude. The First Officer suggested we do a right 360 turn to rejoin and since we were in clear conditions; my brain mistakenly thought we were on a visual approach at that point but forgot that we were still on an IFR clearance. We neglected to contact Denver Center for clearance for a visual approach. Contributing factors were; numerous VFR traffic targets in the pattern at MTJ; busy Unicom radio calls. When we landed safely we then realized that we should have either called Denver Center immediately for a new visual approach clearance or just done the instrument approach missed approach procedure and then called Denver Center during the missed approach. I think both of our minds had reverted to the expectation bias that since it was severe clear during the approach we proceeded as if we were on a visual clearance. This all happened despite the fact that we read and briefed all the published information regarding Montrose; no tower ops and mountain flying guide; together during cruise well before descent. I learned a lot from this situation including that I will now brief exactly what we will do and what is required if there is any kind of change or problem requiring a solution during any approach in non-tower operations. I have some experience flying into mountain no tower airports but this airport has a much higher volume of traffic involved. We felt it was a safer option to turn in a direction that kept us away from traffic on TCAS and visually. We made mistakes with the radio panel as well and had Unicom on both radios.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Air Carrier flight crew reported they were cleared for the RNAV (GPS) Z Runway 17 approach to MTJ in visual conditions. They deviated from their IFR clearance to avoid an aircraft on final without obtaining clearance for a visual approach from Denver Center.