What was found
PIT - FL 1688 - EN ROUTE PIT-ROC, CREW RECEIVED THE MFDU MESSAGE, 'L LG DOWNLOCK SW'. SUBSEQUENTLY, CREW RECEIVED A LANDING GEAR DOWN INDICATION AND A GREEN GEAR LIGHT ON THE MAIN PANEL. FLIGHT RETURNED TO PIT AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE LEFT MAIN LANDING GEAR PRIMARY DOWNLOCK SWITCH. A SATISFACTORY GEAR SWING WAS PERFORMED. (M)