• average run length;
  • statistical process control;
  • unbiased control charts

In this paper, we propose control charts to monitor the Weibull shape parameter β under type II (failure) censoring. This chart scheme is based on the sample ranges of smallest extreme value distributions derived from Weibull processes. We suggest one-sided (high-side or low-side) and two-sided charts, which are unbiased with respect to the average run length (ARL). The control limits for all types of charts depend on the sample size, the number of failures c under type II censoring, the desired stable-process ARL, and the stable-process value of β. This article also considers sample size requirements for phase I in retrospective charts. We investigate the effect of c on the out-of-control ARL. We discuss a simple approach to choosing c by cost minimization. The proposed schemes are then applied to data on the breaking strengths of carbon fibers. Copyright © 2011 John Wiley & Sons, Ltd.