Unmanned Avionics Systems (UAS) are real-time critical embedded systems that include high-integrity requirements. Most of these systems need to be certified before use, particularly in civil airspace. To reduce development cost, some UAS software is developed as part of a Software Product Line (SPL). A product-line comprises a reference architecture and a set of reusable core assets. New systems can be derived from the product-line architecture and core assets based on a predefined process that manages and controls permitted variations, based in part on product-line features defined in a feature model. However, many features are interdependent and hence complicate the analysis of all potential feature combinations for product-line systems. In this paper we discuss the impact of feature dependencies in the safety analysis of unmanned avionics SPLs and present a preliminary model-based solution for managing the impact of these dependencies.