What was found
FLT 9519 - BHM-DCA - RETURNED TO FIELD AFTER THE COCKPIT STARTED FILLING UP WITH SMOKE. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT MADE AN UNEVENTFUL LANDING. MX TROUBLESHOT AND FOUND THE RELAY PROBE HEATER CONTROL RELAY SHORTED. MAINTENANCE IN BHM PULLED AND BANDED THE CIRCUIT BREAKER. THE DISCREPANCY WAS MEL''D. IN DCA MAINTENANCE REMOVED AND REPLACED THE RELAY AND SOCKET. OPS CHECKS GOOD. THE AIRCRAFT WAS RETURNED TO SERVICE. (M)