What was found
N404BC, SN 128, LINE CASUALTY AIRCRAFT RETURNED AFTER BECOMING AIRBORNE. THE CREW REPORTED UNABLE TO RETRACT SLATS. INVESTIGATION REVEALED, THE L/H OUT BOARD SLAT TRACK 8, STOP RETAINING BOLT, WAS LOOSE, CAUSING FOULING WITH LEADING EDGE STRUCTURE AND CAUSING DAMAGE TO L/E STRUCTURE AND BENDING THE SLAT. THIS PREVENTED FULL MOVEMENT OF THE SLAT, BACK TO A CLEAN WING.THIS AIRCRAFT HAS NOT BEEN MAINTAINED BY MAINTENANCE PRIOR TO THE INCIDENT. RECTIFICATION CARRIED OUT AT AINTENANCE SERVICES.