What was found
(CAN) ON APPROACH FLIGHT CREW REPORTED UPON SELECTION OF FLAPS TO NR 1 POSITION THE NR 4 SLAT HUNG UP UNTIL FLAPS WERE SELECTED TO '15' POSITION. ALL INDICATIONS WERE NORMAL AFTER FLAPS '15' SELECTION AND NO CONTROL DIFFICULTIES. MAINTENANCE INSPECTION REVEALED NR 4 SLAT OUTBOARD MAIN TRACK BOLT SHEARED. BOLT REPLACED AND SLAT MOVEMENT AND OPERATIONAL CHECKED PERFORMED IAW MM27-81-00. AIRCRAFT FERRIED TO CALGARY (YYC). MAINTENANCE REPLACED NR 4 SLAT ASSEMBLY, OUTBOARD MAIN TRACK ROLLER ATTACH BOLTS AND TRACK GUIDES IAW 27-81-21. SYSTEM GROUND CHECKED SERVICEABLE. AIRCRAFT RETURNED TO SERVICE WITH NO FURTHER INCIDENTS TO REPORT.