The failure of MTTF in availability evaluation

Abstract

In this paper, a truncated bathtub is proposed to model the failure rate of a product with perfect burn-in. We expose some counter-intuition observations, e.g., increasing the MTTF does not necessarily increase the average and instantaneous availability during the product's lifetime, and the average and instantaneous availability could be improved without changing the MTTF. The MTTF and the steady-state availability are not particularly informative and fail to evaluate the product with time-varying failure rate and short upgrading interval.