What was found
IAH- FLIGHT 4106, WHEN STARTING APU IN THE AIR THE CABIN IS FILLED WITH A STRONG OIL BURNING SMELL (NO SMOKE) FOR SEVERAL MINUTES. MAINTENANCE CLEANED RESIDUAL OIL FROM APU COMPARTMENT, PERFORMED A OPERATIONAL CHECK OF THE APU, NO DEFECTS NOTED. THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.