The cost of unscheduled equipment downtime in lean environments is 5 to 30 times what it was before lean because of the effect this downtime has on lost opportunity, failed shipping schedules and lost sales. Still, maintenance remains the largest or near-largest overhead expense in most lean facilities. Using six sigma’s Y=f(x) problem/cause thinking, and five years of maintenance log information, distilled the seven root causes of most unscheduled downtime and much of scrap and rework (low yield). Six sigma’s DMAIC helped determine ways to eliminate or protect against each root cause. Eliminating these root causes in many facilities has resulted in 70% to 92% reduction of unscheduled downtime. With proper expertise, these methods can be implemented in 30 to 60 days. Author: Howard C. Cooper, Amemco.net, Kaysville, UT.