Unmanned Aerial Vehicle (UAV) networks are increasingly deployed in dense, dynamic airspaces, where reliable collision avoidance is essential for safety and mission continuity. Traditional Automatic Dependent Surveillance–Broadcast (ADS-B) systems provide positional awareness but remain vulnerable to spoofing, packet loss, and malicious interference. This paper presents a blockchain-enabled ADS-B framework that integrates predictive conflict detection and immutable maneuver logging to enhance operational trust and resilience. The proposed system leverages certificateless cryptography and smart contract-based consensus to validate positional data, ensure loss-tolerant delivery, and maintain a tamper-proof ledger of avoidance actions. UAV mobility and communication are modelled in a bounded 3D airspace. Extensive simulations demonstrate that our approach reduces collision probability and packet loss ratio while maintaining high delivery reliability. Comparative analysis against existing schemes shows significant performance gains in both safety and communication robustness. The framework’s modular design allows for seamless integration into UAV networks that provide a scalable pathway toward secure and efficient multi-UAV operations in high-density environments.