A critical concern for ASTOVL aircraft during landing manoeuvres is the deterioration in engine stability margin and performance due to the ingestion of hot gas from the engine exhaust into the engine inlets. This paper describes a methodology for the quantitative accounting of the effect of Hot Gas Ingestion (HGI) on engine stability and performance.To maximise performance and minimise design risk it is essential to have a technology data base to assess the likely HGI characteristics of candidate ASTOVL configurations and to identify measures to minimise HGI. This paper assesses the aircraft design features required to obtain low HGI characteristics for a wide range of ASTOVL configurations.Studies of steady-state CFD methods have commenced to determine their ability to model HGI flow paths of alternative aircraft configurations. The ultimate aim is to produce a user-friendly method to numerically model the time-variant aspects of the flow field for aircraft manoeuvres close to the ground. The approach is reviewed in this paper.