B737 captain reported a dual FMS failure resulted in a diversion.

Attributes
ACN	1711447
Time
Date	201912
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy

Narrative:

Enroute to ZZZ1 at FL340; both captain and first officer FMC issues developed into a situation where the navigation to points became unreliable. Autopilot frequently disengaged; safe operation into ZZZZ1 with IFR operations could not be accomplished. Referenced QRH for FMC fail; non-routine landing; and overweight landing checklists. Priority handling was requested; decision was made to divert to ZZZ2 with VFR conditions; and long runway to perform overweight landing. Landing ZZZ2 uneventful; aircraft taken out of service. Photos of FMC values and indications which may have affected navigation attached.

Original NASA ASRS Text

Title: B737 Captain reported a dual FMS failure resulted in a diversion.

Narrative: Enroute to ZZZ1 at FL340; both Captain and First Officer FMC issues developed into a situation where the navigation to points became unreliable. Autopilot frequently disengaged; safe operation into ZZZZ1 with IFR operations could not be accomplished. Referenced QRH for FMC fail; non-routine landing; and overweight landing checklists. Priority handling was requested; decision was made to divert to ZZZ2 with VFR conditions; and long runway to perform overweight landing. Landing ZZZ2 uneventful; aircraft taken out of service. Photos of FMC values and indications which may have affected navigation attached.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.