Single-level continuous sampling plan (CSP-1), called $\mathrm{A}\mathrm{O}\mathrm{Q}\mathrm{L}$ contour scheme, is constructed on the average outgoing quality limit ( $\mathrm{A}\mathrm{O}\mathrm{Q}\mathrm{L}$) contour. However, for specified in-control process the boundary of feasible continuous sampling scheme is not established in CSP-1. The optimal CSP-1 boundary scheme is established based on the estimator of the proportion of conformance for specified in-control process. The parameters of the boundary scheme are determined by the set of equations constructed with the boundary identical equation and contour identical equation, which will guarantee that the proposed scheme is simultaneously both boundary scheme and contour scheme. The behaviour of the established boundary scheme is discussed and compared with the $\mathrm{A}\mathrm{O}\mathrm{Q}\mathrm{L}$ contour scheme. The optimal CSP-1 boundary scheme can quantitatively control the outgoing quality and tighten the inspection whether the process quality fluctuates towards the deteriorated or the improved direction. For practitioners’ convenience, three tables of the boundary scheme parameters under three quality requirements and three confidence levels are provided. The operating procedure is also presented. A real example is given to verify the effectiveness and feasibility of the proposed boundary scheme.

Although systems engineering processes and standards are widely used in aircraft development programs, traditional requirements’ engineering practice for commercial aircraft does not explicitly address value perceptions and associated information. In this paper, a value-focused approach is proposed to promote a better understanding of customer-value perceptions and their derivation among different levels for value-based requirements engineering of commercial aircraft. The approach is a four-step process starting from initial customer statements to a customer-value model and leading to a system-value model with associated component-value models. A set of theories and methods are introduced in order to resolve different aspects of the approach regarding the appropriate understanding of customer-value perceptions and the establishment of the value-based requirements’ specification. A case study is used to demonstrate the transformation of airlines’ initial expectation statements into three types of value models. There are two significant benefits of this approach: (a) perceived customer value can be explicitly modeled, simulated, and derived into different levels of the system development and (b) the value model can be subsequently utilized reactively for design evaluations and proactively for design optimization to generate creative design alternatives.