As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SMOKE IN CABIN REPORTED BY PASSENGERS. PASSENGERS BELIEVE THE SOURCE MAY HAVE BEEN THE FLOOR VENTS. PILOTS COULD NOT CONFIRM SMOKE, BUT RETURNED TO FAIRBANKS IMMEDIATELY AFTER DEPARTURE. CONFIRMED AFT VENT MOTOR AS CAUSE OF SMOKE. REMOVED BAD MOTOR INSTALLED OVERHAULED MOTOR. GROUND OPERATIONAL CHECKS IN LOW AND HIGH SATISFACTORY.