Narrative:

Center had cleared us to descend from FL310 to FL240; as we started to go down both autopilot and autothrottle disengaged; at that time the altitude alert went off; because the MCP showed 50;000 ft; I tried to regain the MCP back but all functions were frozen: heading; speed; [and] course. I looked for a warning light to give me an indication of what the problem was; but there were no warnings; the FMC's had a disagree indication between them; also the map mode was degraded showing some movement then it would freeze; then the FMC gave us another disagreement indication. We informed ATC that we had lost all automation and could we go down to 10;000 ft; at this point I declared an emergency even though we were VMC; but I needed another set of eyes to help guide us while we worked on the problem.both flight directors went off and we were unable to regain them back; as we continued to descend because the altitude window had 50;000 ft in it we kept getting altitude alerts (very annoying). ATC asked for sob and fuel; and that they were setting us up for the ILS approach with the trucks standing by; we continued to work on the problem not knowing which side had failed. I tried to switch both on 1 or both on 2; for the control panel; FMC; IRS; etc. With no luck. The first officer was manually flying the aircraft following ATC's instructions. I had set up both navaids for the approach; I was unable to get an ident on the frequency however when I reached the gate and set the parking brake; the ident came on.

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Original NASA ASRS Text

Title: B737 Captain reported losing FMS capability. He declared an emergency and a safe landing ensued.

Narrative: Center had cleared us to descend from FL310 to FL240; as we started to go down both autopilot and autothrottle disengaged; at that time the altitude alert went off; because the MCP showed 50;000 FT; I tried to regain the MCP back but all functions were frozen: Heading; speed; [and] course. I looked for a warning light to give me an indication of what the problem was; but there were no warnings; the FMC's had a disagree indication between them; also the map mode was degraded showing some movement then it would freeze; then the FMC gave us another disagreement indication. We informed ATC that we had lost all automation and could we go down to 10;000 FT; at this point I declared an emergency even though we were VMC; but I needed another set of eyes to help guide us while we worked on the problem.Both flight directors went off and we were unable to regain them back; as we continued to descend because the altitude window had 50;000 FT in it we kept getting altitude alerts (very annoying). ATC asked for SOB and fuel; and that they were setting us up for the ILS approach with the trucks standing by; we continued to work on the problem not knowing which side had failed. I tried to switch both on 1 or both on 2; for the control panel; FMC; IRS; etc. with no luck. The First Officer was manually flying the aircraft following ATC's instructions. I had set up both navaids for the approach; I was unable to get an Ident on the frequency however when I reached the gate and set the parking brake; the Ident came on.

Data retrieved from NASA's ASRS site as of July 2013 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.