What was found
(CAN) ENROUTE CREW REPORTED A STRONG ODOR IN THE FLIGHT DECK. CREW FOLLOWED QRH FOR ODOR IN FLIGHT DECK AND WAS UNABLE TO ISOLATE THE FAULT AND THEREFORE RETURNED TO DEPARTURE. CONTRACT MAINTENANCE CARRIED OUT FIM 21-00, TASK 806 FOR FUMES IN THE CABIN, UNKNOWN SOURCE AND NO FAULTS WERE FOUND. CREW CARRIED OUT ENGINE RUNS AND WAS UNABLE TO DUPLICATE A SMELL. ACFT WAS REPOSITIONED AND DURING REPOSITIONING NO ODORS WERE NOTED. SUSPECTED UNKNOWN ENVIRONMENTAL ODOR MAY HAVE CONTRIBUTED TO THE EVENT. ACFT HAS CARRIED OUT ADDITIONAL FLIGHTS WITH NO FURTHER ODOR REPORTED.