What was found
VERY LOUD WHISTLE OUT OF NR 3 COCKPIT WINDOW, RIGHT REAR WINDOW ON FO SIDE WAS NOTICED ON DEPT AND ARRIVAL WITH CAB DIFF PRESS AT 5.O. *S/D* DUE TO SQUEALING, THE WINDOW WAS REMOVED AND CORROSION DAMAGE WAS FOUND AT THE LOWER AFT CORNER STA 338. THE DAMAGE WAS CONTAINED IN THE UPPER OUTBOARD FLANGE OF THE LOWER SILL. THE CORROSION REMOVAL RESULTED IN A 3 INCH SECTION OF THE FLANGE BEING TRIMMED OFF REVEALING A 3 INCH LONG CRACK. THE SILL WAS REPLACED.