What was found
(CAN) THEY ORIGINALLY REPORTED OIL ODOR AND VISIBLE VAPORS AFTER START. IT ALSO REOCCURRED AT THE TOP OF DESCENT OR APPROACH. THE TOILET SMOKE DETECTOR WAS ALSO ACTIVATED. A THOROUGH BORESCOPE INSPECTION HAS BEEN CARRIED OUT ON BOTH ENGINES. THEY HAVE NOT FOUND ANY CONCLUSIVE EVIDENCE OF AN OIL LEAK IN EITHER ENGINE. A CHECK OF THE AIR CYCLE MACHINES HAS FOUND SOME OIL STAINING ON AT LEAST ONE PACK. THEY CHANGED THE AFT PACK AND THE AIRCRAFT IS CURRENTLY ON A PROVING FLIGHT WHERE THE CREW HAVE BEEN INSTRUCTED TO THOROUGHLY TEST THE BLEED SYSTEM AND BOTH PACKS INDIVIDUALLY.