The two flight control computers each have two flight control channels, which each deal with pitch, roll and yaw (the independent failure of one axis control does not affect the others). In the absence of normal control augmentation system (CAS) function, each computer also provides a direct electrical link (DEL) between stick inputs and flight control surfaces. If roll or yaw digital DEL fails, the computers provide an analog DEL to the ailerons and rudders.
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Likewise, if pitch digital DEL fails, a direct mechanical backup (MECH ON) conveys stick inputs to the differential stabilator actuators provides the pilot some degree of pitch and roll control in an extreme emergency. In addition to a complete four-system collapse (such as inoperative ailerons and rudders and complete electrical, including battery, failure), the pilot can also deliberately choose this option. Battery power conservation for landing purposes is one such example. Guided by experience from Vietnam, duplicate hydraulic systems are routed separately as much as possible. This arrangement diminishes the likelihood that a single hit may disable the aircraft.
