Abstract:  Laminar-turbulent transition is a critical phenomenon in aerodynamic flows and can have a leading-order impact on flight vehicle performance. In many cases of practical interest, prediction of transition from first principles can be prohibitively difficult due to high Reynolds numbers, geometric complexities, and inherent unsteadiness limiting the ability to perform direct numerical simulations or detailed stability analysis. In response to these challenges, there is great interest by the aerodynamics community in PDE-based transition models that are fully compatible with industrial computational fluid dynamics solvers. Although boundary-layer transition is widely accepted to be a non-local phenomenon, PDE-based models are generally phenomenological in nature and are built on single-point correlations. Such models may be used without excessive increases in grid resolution or sacrificing parallel scalability, and they may be applied to general three-dimensional aerodynamic configurations with minimal user intervention. An overview of leading PDE-based models will be presented, including the amplification factor transport (AFT) model developed by the presenter. The AFT model has been successfully applied to a wide range of engineering applications including the design of NASA’s Ingenuity Mars helicopter. A brief summary of results and lessons learned from the 1st AIAA CFD Transition Modeling and Prediction Workshop will also be presented.