As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DEPARTED COPENHAGEN ON ATTEMPT TO CARRY OUT A POSITIONING FLIGHT (SK9100), COPY FROM PILOTS (FOR):- SHORTLY AFTER TAKEOFF WE HEARD SMOKE WARNING FROM LAVATORY. INSPECTION REVEALED NO SMOKE OR FIRE.AND FLIGHT RETURNED TO COPENHAGEN FOR TECHNICAL INVESTIGATION.THE LAVATORY SMOKE DETECTOR IS SENSITIVE TO ENGINE FUMES AND BOTH ENGINES PRIOR TO THIS FLIGHT WERE PRE-MOD (S/B 35038).