What was found
FLIGHT 1728, AFTER TAKEOFF CABIN & COCKPIT CREW HAD UNUSUAL ODOR COMING FROM CABIN & COCKPIT, SEEMED TO SUBSIDE IN CABIN WHILE IN CRUISE, BUT REMAINED SOMEWHAT STRONG IN THE COCKPIT. THE FLIGHT CREW WENT ON OXYGEN, WHILE IN DESCENT STRONG ODOR RETURNED AGAIN TO CABIN. MAINTENANCE RAN BOTH THE LEFT AND RIGHT ENGINE WITH NO ODOR DETECTED.