Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 94; Flight Crew Total 16500; Flight Crew Type 4099
Situational Awareness; Distraction
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural FAR; Inflight Event / Encounter Weather / Turbulence
Flight Crew Returned To Clearance
Human Factors; Weather
2 hours into cruise on B474 we received clearance to deviate up to 20 NM right of track to avoid weather. This deviation would require a bit of a weave so we elected to use heading within the bounds of the right 20 offset entered into the FMS. We had successfully navigated around the most significant cell and were making a turn back toward the route at the edge of a layer of alto cumulus. Pilot Flying (PF) was changing heading frequently to maximize our distance from the main cell and attempt to keep us in the clear to the left of the turbulent alto cumulus. We entered the edge of the clouds with the IGN OVRD on in case of turbulence. I felt the power come back and looked in to see a magenta speed FMA of .817 which I thought was in response to an FMS speed intervene made by PF to place us in turbulent speed penetration range. A few seconds later PF stated 'Why are we descending?' We both realized that the Flight Control Panel (FCP) altitude had been changed and that we were in level change as a result of turning and pulling the wrong knob to effect a heading change. A correction was made via FCP but the altitude deviation was approximately 750 feet. Minutes later; we were back on course at FL320 without further issue. Both pilots focused too much on weather outside instead of bringing focus to the FCP when a change was being made. New emphasis is being made for PM to be looking for something rather than looking at something (Flight Path Monitoring Guide) - this is a good example of doing that wrong in cruise (green area of vulnerability).
[Report narrative contained no additional information].
Air carrier flight crew meant to change the heading while deviating around weather; but descended in level change as a result of turning and pulling the wrong knob.