User blog comment:Ziebro/Normal Humans in Astartes chapters?/@comment-173.79.66.99-20130202130517/@comment-3258762-20130203121114

The amount of skill and the level of reflexes needed to man an Astartes Thunderhawk is too much for a normal human.

Not to mention that Astartes would almost never allow normal humans to controll their most venerable warmachines.