What was found
THE CREW REPORTED THAT WHILE PERFORMING A MAINTENANCE TEST FLIGHT TO CHECK FLAP ROLL RATE, A HOT OILY SMELL WAS NOTED IN THE COCKPIT AS COMING FROM A WEMAC AIR VENT. THE SMELL WAS STRONGEST ON TAKEOFF, BUT EVIDENT IN ALL FLIGHT PHASES. ALL OTHER INDICATIONS, INCLUDING PRESSURIZATION AND ENVIRONMENTAL SYSTEMS WERE NORMAL. MAINTENANCE REPLACED THE NR 1 ENGINE DUE TO THE DISCOVERY OF OIL IN THE INTERNAL FAN BYPASS. ALL ENGINE OPERATIONAL CHECKS PERFORMED WERE WITHIN LIMITATIONS. THE AIRCRAFT WAS RETURNED TO SERVICE.