What was found
PHL FLT 722 EN ROUTE PHL TO DUB. THE RIGHT WINDOW (F/O) HEAT WAS INOPERATIVE WITH THE SWITCH ON, AND NO INOP ILLUMINATED ON THE SWITCH. ABOUT HALF WAY BETWEEN THE LAST TWO CONNECTORS ON THE LEFT SIDE OF THE WINDOW, A SMALL ARCING COULD BE SEEN. THE RIGHT WINDOW DEVELOPED CRACKS AS A RESULT OF THE ARCING. THE FLIGHT COULD NOT CONTINUE INTO ICING CONDITIONS THAT WERE EXPECTED EN ROUTE TO DUB, SO THE FLIGHT RETURNED TO PHL AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE RIGHT WINDOW HEAT CONTROLLER (AS A PRECAUTION), AND THE FIRST OFFICER'S WINDSHIELD.