What was found
WHILE EN-ROUTE AT FL400 WE RECEIVED THE WHITE CAS MSG AHARS 1 & 2 FAULT. UNDER THE MSG PAGE ON THE GTC WAS INDICATING GPS NAVIGATION SIGNALS WERE LOST. APPROX 10 MINUTES LATER WE RECEIVED THE YELLOW YD FAIL AP FAIL SWPS FAIL & WHITE VENTRAL RUDDER FAIL. THE ACFT ENTERED A DUTCH ROLL WHICH WAS MOSTLY CONTROLLABLE. WE DESCENDED TO FL250 & REGAINED CONTROL OF THE ACFT OUT OF FL290 APPROX. SOMEWHERE AROUND 25000 FEET THE CAS MSGS DISAPPEARED & STAYED OFF FOR THE REMAINDER OF THE FLIGHT.