a helmet for aircrew in a highly manueverable aircraft has six air bags which are inflated or deflated by a control system so as to counteract acceleration forces on the wearer &# 39 ; s head and helmet . two pairs of air bags engage the wearer &# 39 ; s body , and two bags engage the seat headrest so that restoring forces in yaw , pitch and lateral directions can be applied . a position sensor determines the actual position of the helmet which is compared with the predicted position , as derived from an inertial sensor or inputs from the aircraft flight control system , the difference between these two positions being used to control operation of the air bags . a memory module programmed with information about the behavior of the wearer &# 39 ; s head and helmet characterizes the control system to the particular wearer and is removable for use in other systems .