Wright Williams & Kelly
TECHNICAL ALERT #15
Unscheduled Repair Time
All versions of TWO COOL® make the assumption that each unscheduled repair includes an equipment requalification test. This assumption is the same one that was used in SEMATECH revision B. Thus, total downtime for each unscheduled repair is the sum of mean time to repair (MTTR) and mean time to test (MTTT).
If your estimates of MTTR include requalification test time, either set MTTT=0 or reduce the MTTR estimate by MTTT. To completely exclude repair time from an analysis, both MTTR and MTTT must be set to zero.