Airworthiness Directives; Cessna Model 680 Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Cessna Model 680 airplanes. This AD requires revising the airplane flight manual (AFM) to add procedures to facilitate recovery of the cockpit display units in the event that the cockpit display units go blank, and to add flight crew briefings on the use of standby instruments in case the cockpit display units go blank and do not recover. This AD also requires repetitive tests of the avionics standard communication bus (ASCB) for any failures, and corrective action if any failure is found. This AD also requires installing hardware and avionics software upgrades; installing the upgrades will allow removal of AFM revisions and will end the repetitive inspections of the ASCB. This AD is prompted by a report indicating that analysis of the Honeywell Primus Epic systems installed on Cessna Model 680 airplanes revealed that all four of the cockpit display units could go blank simultaneously. We are issuing this AD to prevent a simultaneous loss of data from all four cockpit display units, and loss of primary navigation instruments, autopilot, flight director, master caution/ warning lights, aural warnings, global positioning system position information, and air data and altitude information to non-avionics systems. These losses could reduce the flightcrew's situational awareness, increase flightcrew workload, and consequently reduce the ability to maintain safe flight of the airplane.