Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Confusion; Situational Awareness; Communication Breakdown
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Manuals; Procedure; Human Factors
ATC assigned a deviation right of course and then a direct to a fix when clearing severe weather. After clearing the first major buildup on our current heading a build up on our current course appeared and we then turned left (still right of course by at least 20 miles) but we did so without advising ATC. I can't say how much time elapsed but I'd guess 2 to 5 minutes. ATC called us up and asked if we had changed our heading and we indicated that we had turned left to avoid a buildup in front of us. The Controller did not seem happy that we didn't notify him. The Captain seemed expressed that although we were still right of course and did move in the interest of safety that we should submit a report. Shortly after the conversation we cleared the weather and went direct to our next fix and ATC did not say anything else. Lack of communication. Advise ATC immediately if changing heading to avoid severe weather.
An Air Carrier pilot deviating right of course for weather reported ATC questioned them when they turned left for further deviations.