Abstract: An indexing mechanism for use with a deployment mechanism of a ram air turbine having front and rear linkages pivotally connected at one of their ends within the storage bay of an aircraft and their other ends pivotally connected to a housing for the ram air turbine, for moving the ram air turbine between a stowed and deployed position. The improved indexing mechanism includes a spring-loaded detent member coupled to the housing which engages a slot in the turbine hub preventing rotation of the turbine hub and blade when the ram air turbine is in the stowed position. Coupled to the rear linkage adjacent the pivot joint at the ram air turbine is a cam member which moves through an arc as the ram air turbine is deployed, said cam member engaging the spring-loaded detent member to release the turbine hub and blade as the ram air turbine nears the fully deployed position.