Date: 202105
Local time of day: 0601-1200
Location: P50.TRACON, AZ
Flight conditions: VMC
Aircraft: Light Transport
Operator: Air Carrier
Operating under: Part 135
Flight phase: Climb; Initial Climb
Airspace: Class E P50
ATC / advisory: TRACON P50
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Commercial; Flight Crew Instrument
Human factors: Situational Awareness; Confusion; Communication Breakdown
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: IFR flight to ZZZ. Weather was not a factor. Departed PHX from Runway 7R; runway heading assigned. After approaching 1;000 feet AGL; assigned heading 050. Switched to Phoenix Departure on 119.2; then 120.7 within a minute or two. Controller gave me instructions to 'turn left heading 360; vectors to intercept the PXR 350 radial.' Knowing I was on a diverging path away from my flight-planned route; I was waiting for at least one more turn that would take me toward the radial. This turn occurred within the next few minutes with the controller saying 'turn left heading 270'. Now on an intercept heading with the radial; I made a right turn to join the PXR 350. The Departure Controller quickly gave me instructions to fly heading 260 (which I immediately complied with) asking why I had made the turn north. The remainder of the flight occurred without incident.In hindsight; here's what I learned during this exchange. Despite the numerous flight hours operating in the PHX ATC system; I somehow mistakenly interpreted 'intercept' with 'join'. I knew a 360 heading would not intercept the planned radial. So; I was expecting that next turn to put me on course to do so. What I wasn't told; was the 270 heading was for spacing from other traffic; not necessarily to intercept or join the PXR 350 radial. Had I known why (traffic) I was being turned to a 270 heading; then my thought process would've completely changed and I would've known; without question; to continue on the assigned heading. Instead; I was thinking this was simply the heading that would allow me to intercept the 350 radial. Despite my error; I should have questioned the heading as the intercept angle was 80 degrees; not the standard 30 degrees one would expect. In doing so; the Controller would have simply advised me to remain on the 270 heading and expect another turn to intercept and join the airway. As pilots; we must deal with many human factors on a daily basis. Some of those factors thwart our efforts to fly safe and reasonably. I feel this was a situation where 'if it doesn't look right or feels oddly different' then say something. Questions are always free. Accidents are costly. Routinely flying the same routes and hearing the same instructions from ATC can also create a unique set of issues. We don't always hear what was said; we hear what we expect. And this human factor is one that all pilots must concentrate on avoiding.




Synopsis: Light Transport aircraft Captain reported deviation from clearance during climbout.