What was found
ORD - FLT 854 - EN ROUTE FLL-ORD, ON APPROACH ORD, AFTER PUTTING LANDING GEAR HANDLE DOWN. RGHT GEAR WARNING LIGHT ILLUMINATED. USED MANUAL GEAR EXTENSION TO EXTEND LANDING GEAR. GEAR SHOWED DOWN AND LOCKED. LANDED ORD WITHOUT INCIDENT. REPLACED D1-27 SENSOR. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)