The Aircraft Reply and Interference Environment Simulator (ARIES) makes possible the performance assessment of a Discrete Address Beacon System (DABS) sensor under its specified maximum aircraft load. To do this ARIES operates upon a taped traffic model to generate simulated aircraft replies and fruit, feeding them to the sensor at RF. Support documentation for ARIES, of which this is the first volume, consists of: Volume 1: Principles of Operation Volume 2: Appendices to the Principles of Operation Volume 3: Programmer's Manual The Principles of Operation details the operation of ARIES hardware and software. Descriptive information, supported by block diagrams, simplified schematic diagrams and flow diagrams, is provided sufficient to permit a thorough understanding of ARIES operation.