What are the main phases of the aircraft design process?

Aircraft design progresses through three main phases: Conceptual Design - Establishes mission requirements, explores configurations, and creates initial sizing (wing area, engine thrust, weights). Key decisions on configuration are made here with rough analysis. Preliminary Design - Refines the selected concept with detailed aerodynamic, structural, and systems analysis. Wind tunnel testing begins, major systems are defined, and the design is frozen for detail design. Detail Design - Produces manufacturing drawings, specifies parts and processes, and prepares for production. Each phase progressively increases design definition while decreasing flexibility for changes. Design reviews (PDR, CDR) gate progression between phases.