MD-82
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Overcame Equipment Problem
Aircraft
Last evening both FMS's involuntarily went to the menu page. I consulted the QRH; but no procedure seemed to fit the behavior observed in the FMS's. I played with the FMS for several minutes. I couldn't get it to unlock itself. When I felt that I had exhausted all options; I felt that it wasn't a good idea to continue to [destination] in this condition. I [advised ATC and] diverted to [a nearby alternate]. However after going into heading select the FMS anomaly corrected itself. I cannot explain why. That is a mystery. I still had enough fuel to make [the original destination]; so I decided to continue. I brought all of this to the attention of ATC. The rest of the flight was uneventful.
MD-82 Captain reported both FMS's locked up for an unspecified period of time; but then returned to normal operation.