As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
YUL - FLT 4005 - THE CREW REPORTED SMOKE IN CABIN AND COCKPIT. THE AIRCRAFT RETURNED TO YUL AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE PERFORMED OPERATIONAL CHECKS OF THE AIR CONDITION SYSTEM IAW 21-00-00. NO DEFECTS WERE NOTED. THE AIRCRAFT WAS RELEASED FOR SERVICE. (M)