B737-800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
About 3 hours into cruise First Officer's PFD display started to give erroneous information including groundspeed; winds; vertical speed indications and warning flags. We also noticed all three attitude indicators showed a slight left bank. There were no other warning lights until about 20 minutes later the 'Fault' light for the right Inertial Reference System (IRS) came on. As this progressed it was apparent that our navigation was beginning to degrade because ATC said we were still heading in the right direction; but slightly off course. Eventually we completely lost the First Officer's PFD attitude display and both autopilots. Given the distance to our destination; weather; night time; degraded instrumentation and no autopilots; we decided to [advise ATC] and divert to [a nearby alternate] where the weather was clear. During descent and approach it became apparent yaw damper was inoperative also. Finally during rollout the stick shaker activated.
B737-800 pilot reported they diverted to an alternate airport after experiencing degraded flight data information.