B737-800
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Total 20000
Aircraft Equipment Problem Less Severe
Air Traffic Control Issued New Clearance; Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed
Aircraft
Dual FMC (Flight Management Computer) failure. We thought the FMC's would come back in a minute or two; but they did not. We called Center and asked for vectors back to [departure airport]; explaining our dual FMC failure. We went through QRH procedures; but were unable to recover the FMC's. CA (Captain) screen was blank. FO (First Officer) could see airport identifiers on his. We had a VTK (Vertical track) and Landing Alt amber lights on the PFD (Primary Flight Display). About 35-40 minutes later; ACARS messages started printing indicating to me; the aircraft thought it was on the ground. I got a close-out deleted and expired messages. I had selected both FMC's to FO side as per QRH with that side giving best information. After the close out deleted message; I was able to reload the Perf Init page and everything came back to normal; except the amber landing alt and no amber hook on CA side. We continued to [departure airport] and landed uneventfully.I suspect the aircraft had a failure which may have been caused by system failure indicating we were on the ground. Or perhaps that was a result of another failure with the FMC's.
B737-800 Captain reported returning to departure airport after experiencing a dual FMC failure.