This paper is motivated by Food Safety Modernization Act, signed into law by President Obama on Jan. 4, 2011, after several outbreaks of tainted foods have cost human health and contracted food‐industry prosperity over the past decade. It develops a situationally sample‐size‐adjusted procedure, called a tightened–normal–tightened (TNT) sampling strategy, on the basis of yield‐index (Spk) verification of the production process, whose measurements, garnered from a key quality characteristic with bilateral specification limits, follow a normal distribution. In this paper, we firstly describe the sampling procedure of the Spk ‐ TNT(nT, nN, k) inspection scheme whose sets of parameters include sample sizes for the tightened inspection (nT) and normal inspection (nN), and the critical value (k). Those parameters are determined from the joint solution of two nonlinear inequalities complying with the tolerable vendor's risk, buyer's risk, the desired acceptable quality level (AQL) and limiting quality level (LQL). Then, the proposed Spk ‐ TNT(nT, nN, k) schemes for several inspection standards, widely utilized in practice, are delineated, and their functioning behaviors and propensities are further investigated. Moreover, we compare the Spk ‐ TNT(nT, nN, k) strategy with two unadjusted inspection schemes, Spk‐tightened, Spk ‐ T(nT, k), and Spk‐normal, Spk ‐ N(nN, k), to illustrate its inspection flexibility and efficiency in real applications. Finally, implementing with a vendor–buyer contract agreement using the Spk ‐ TNT(nT, nN, k) sampling plan, a company inspecting the submitted universal‐serial‐bus (USB) connectors demonstrates the applicability of our proposed methodologies.
