THE MAIN PRODUCTION HOIST WAS TAKEN OUT OF SERVICE THE MORNING OF 10/21/2011 AT 7:00AM TO PERFORM HYDRAULIC SYSTEM MAINTENANCE. AT 6:05AM, THE MSHA 1-800# WAS CALLED BY AN EE TO ADVISE THEM OF THE SITUATION. THE HOIST WAS PLACED BACK INTO SERVICE AT 5:40PM. NO INJURIES OR ACCIDENTS ONLY THE HYDRAULIC MAINTENANCE WAS PERFORMED.