F-16 Flight Control System Redundancy Concepts

The F-16 Air Combat Fighter uses relaxed longitudinal static stability concepts to realize maximum performance. Because of the static instability associated with the RSS system it is essential that redundancy be employed for safety reasons. The F-16 Flight Control System (FCS) is a quad branch fly-by-­wire system that is required to be operative following two like electronic failures. The redundant branches provide the system back up necessary for safe operation by rejecting the output from a branch that disagrees with two others, and then selecting the middle value of the remaining three. The active signal selector used for this function is the heart of the Flight Control electronic redundancy management. Triple redundant air data source information is selected and expanded to quad branch data for programming FCS gains. The source for this data is a dual pitot-static nose probe, two radome mounted angle of attack transmitters, a fuselage mounted hemispherical head probe, and a pneumatic sensor assembly for converting pneumatic data to electrical signals. The servo amplifier outputs are monitored and, in the event of a discrepant output, the malfunctioning circuit is replaced to the servo valve by use of a standby servo amplifier to a secondary servo valve coil. The hydraulic servo that receives redundant inputs con­tains its internal hydraulic monitoring to negate a failed output. The monitors used to observe the health of the system are also used for built-in-test. The adequacy of the system, prior to operation, is verified by torquing certain input sensors and observing the monitors and surfaces for proper response.