Question

Is it possible for LCLx in an Xbar chart to be greater (>) than an upper specification limit (USL)?

Answer 1

Yes

Theoretically, it is possible for LCLx in an Xbar chart to be greater than USL. This happens, when the process is not centered and the mean of the process is greater than USL, by at least 3 standard deviations. The process may still be in statistical control, but it will not be capable of producing output within specification, because 99.73% of the output will be greater than USL. However, practically, when a process goes so much off center, that its mean becomes greater than USL, then such a process will to be allowed to run. So, it is nearly impossible to experience such an instance in practical life.