What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND TRHGE AIRCRAFT RETURNED TO PHL DUE TO THE FLIGHT CREW REPORTING THAT AN ODOR WAS PRESENT IN THE AFT CABIN INITIALLY AFTER ENGINE START BUT QUICKLY DISSIPATED HOWEVER AFTER TAKE OFF THE FLIGHT ATTENDANTS REPORTED WITHIN APPROXIMATELY THE FIRST MINUTE OF FLIGHT THE ODOR RETURNED - THE FLIGHT ATTENDANTS DESCRIBED THE ODOR AS A FAINT PLASTIC" SMELL - THE AIRCRAFT LANDED SAFELY AT PHL WITHOUT FURTHER INCIDENT - MAINTENANCE REPORTED THAT THE APU IS CURRENTLY ON MEL AND SUSPECT THAT IT MAY BE THE SOURCE OF THE ODOR (OPEN)