The performance of a helicopter engine depends essentially on the performance of the high-pressureturbine, closely correlated with the rotor/stator clearance at the tip of the blades. The engine’sthermodynamic cycle causes elastic or plastic strains on some of the high-pressure turbine components,causing considerable geometric variations, some of which are irreversible.In this article we propose to integrate the notion of behaviour into the evaluation of clearance in a highpressureturbine by defining the physical phenomena that are influential during certain operational phasesand more generally over the lifetime of the turbine. Modelling the variations in the geometric deviations ofthe parts and the contacts is based on deviation hulls and clearance hulls.