Medium Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Distraction; Situational Awareness; Confusion
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Returned To Clearance
Human Factors
We were cleared to descend via the FQM3 Williamsport 3 Arrival into Newark. We were descending to RACKI at 13;000 out of 18;000 ft we encountered significant wake turbulence at the same time we were receiving a cup of coffee from the Galley. The coffee spilled and in the course of the Captain cleaning up the spill I glanced down to see how much coffee had spilled. During the clean up the TKNB knob was hit inadvertently. The aircraft started a slow turn left of course in continuous chop in what seemed to be a wind correction. I observed the winds had shifted to the left side of the course. As the aircraft continued to turn I verbalized; 'what is this doing?' The aircraft was now approaching 1 dot deflection from course and I attempted to correct first on the flight guidance panel to RE-NAV the course. The aircraft did not respond I attempted no further changes to the panel and instead disconnected the autopilot to return the aircraft to course. We were now at one dot deflection and correcting to course. While doing so ATC called us to say they noticed we were left of course and issued us a 150 degree heading to rejoin the course. We complied with the instruction. We saw the TKNB annunciation on the PFD and the Captain reset it. I rejoined the course and we verified our position on the descent for the arrival. We continued the arrival and descent without further incident.
First Officer reported the Captain inadvertently selected the turn knob (TKNB) while cleaning up a coffee spill which resulted in drifting off the arrival course into EWR.