When outsourcing design tasks, firms want their suppliers to be both efficient and adaptive. Whereas efficiency is necessary to reap economic gains from outsourcing, adaptation is required to deal with interdependencies as the design evolves. Achieving both objectives simultaneously, however, is difficult because procurement contracts require a trade-off between providing incentives for efficiency and facilitating adaptation. In the presence of formal contracts that provide strong incentives for efficiency, ensuring adaptation thus requires effective relational contracts between the buyer and the supplier. But because the focus of prior research has been on dyadic buyer–supplier relationships, it is unclear how the efficiency–adaptation trade-off can be mitigated in the multitier supplier systems that are common in many industries. Addressing this gap, we argue that in hierarchical supplier systems, relational contracts between contractual partners become more important, but at the same time harder to establish, than in single-tier supplier systems. An in-depth case study of the adaptive frictions that arose in the Airbus A350 program allows us to illustrate this challenge of tiered outsourcing. Moreover, we show how Airbus came to resolve the frictions by leveraging skip-level ties—direct informal contacts to lower-level suppliers with which no contractual relationship existed, thus replacing the archetypal notion of a supplier hierarchy by a more complex relationship structure. We discuss the boundary conditions of our findings and suggest propositions for the emergence of skip-level ties in tiered outsourcing.