We use a new firm level dataset to study the network of formal firm linkages within and across 52 aerospace clusters in North America and Europe over the period 2002-2014. Applying community structure detection techniques, we find that the structure of the overall network has changed over time. We organize sub-networks by linkage type and find two important trends in their evolution. First, new linkages in the vertical buyer-supplier sub-network are generally formed in a hierarchical hub-and-spoke fashion, whereas new links in the horizontal partnership sub-network are generated in a more decentralized and cohesive manner. Second, the geographical scope of new linkages is different, with vertical buyer-supplier and investment linkages moving increasingly trans-local and partnership linkages becoming more localized. Taken together, our findings suggest that the overall network is evolving from a geographically partitioned community structure to a hierarchical community structure that is stratified along value chain stages.