What was found
DURING APPROACH FOR LANDING INTO GRR, THE SLAT DISAGREEMENT LIGHT REMAINED ILLUMINATED AND THE AIRCRAFT ROLLED TO THE LEFT. FLIGHT CREW COMPLIED WITH COM PROCEDURES AND ACCOMPLISHED AN UNEVENTFUL NO SLAT LANDING AT GRR. CONTRACT MAINTENANCE COULD NOT FIND ANY ABNORMALITIES AND COULD NOT DUPLICATE THE PROBLEM. ALL CHECKS WERE NORMAL. THE AIRCRAFT WAS CLEARED FOR FERRY FLIGHT AND PROBLEM REPEATED ON APPROACH INTO DTW. DTW MAINTENANCE NOTED A SLIGHT RATCHETING ON THE RIGHT T-DUCT DURING OPERATION. THE T-DUCT WAS REPLACED AND THE AIRCRAFT RETURNED TO SERVICE.