Narrative:

Before descent at FL260; we had some sparking and snapping noises around the captain's forward window. Then we lost the autoplt; autothrottles; both flight directors; and all MCP windows and switches were frozen; with the exception of the first officer's course window. The ILS runway xx GS was OTS and the WX was right at 3 mi and 1000 ft or less; below our required minimums. The WX was reported at 6000 ft ceilings and 15 mi visibility. We declared an emergency; and proceeded direct to the VOR using the RMI's. We flew the lda DME runway xx approach. We broke out on downwind at 5500 ft into VFR conditions and continued to an uneventful landing. I am not sure what caused the MCP to fail; and there were no QRH checklists for this situation. Loss of MCP; loss of autothrottles; autoplt; flight director; all MCP windows froze except first officer's course window. Callback conversation with reporter revealed the following information: the reporter did not know precisely what caused the failure but believes an electrical short circuit of some sort was involved. Static that was heard in the headset prior to the failure completely went away once the MCP failed. Supplemental information from acn 801309: while en route (FL260); just before top of descent; we realized that the MCP had frozen except the course selector on my side. The autoplt; autothrottles and flight directors disengaged on their own. At ZZZ the ILS had the GS OTS and WX was right at or slightly below minimums for the ILS GS OTS non-precision approach. The captain decided that we needed to find an alternate with better WX. We were informed that aircraft had just arrived at ZZZ1 under VFR conditions 6000 ft ceilings and 15 mi visibility. Due to the greatly reduced navigation abilities of our airplane; ZZZ1 was the most prudent and timely alternative. An emergency was declared; we then proceeded direct to VOR and set up for the lda DME. We flew the approach with the DME arc transition and broke into the VFR conditions and proceeded on the approach to the airport and landed without further incident. I don't think that an MCP failure can be avoided or foreseen; but more time during training could be spent flying raw data without autoplt; flight directors and rnp approachs. We were also not able to find any reference to an MCP failure in the QRH.

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Original NASA ASRS Text

Title: B737 FLT CREW REPORTS MCP FAILURE AT FL260 AND DIVERSION TO VMC ARPT FOR LANDING.

Narrative: BEFORE DSCNT AT FL260; WE HAD SOME SPARKING AND SNAPPING NOISES AROUND THE CAPT'S FORWARD WINDOW. THEN WE LOST THE AUTOPLT; AUTOTHROTTLES; BOTH FLT DIRECTORS; AND ALL MCP WINDOWS AND SWITCHES WERE FROZEN; WITH THE EXCEPTION OF THE FO'S COURSE WINDOW. THE ILS RWY XX GS WAS OTS AND THE WX WAS RIGHT AT 3 MI AND 1000 FT OR LESS; BELOW OUR REQUIRED MINIMUMS. THE WX WAS RPTED AT 6000 FT CEILINGS AND 15 MI VISIBILITY. WE DECLARED AN EMER; AND PROCEEDED DIRECT TO THE VOR USING THE RMI'S. WE FLEW THE LDA DME RWY XX APCH. WE BROKE OUT ON DOWNWIND AT 5500 FT INTO VFR CONDITIONS AND CONTINUED TO AN UNEVENTFUL LNDG. I AM NOT SURE WHAT CAUSED THE MCP TO FAIL; AND THERE WERE NO QRH CHKLISTS FOR THIS SITUATION. LOSS OF MCP; LOSS OF AUTOTHROTTLES; AUTOPLT; FLT DIRECTOR; ALL MCP WINDOWS FROZE EXCEPT FO'S COURSE WINDOW. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER DID NOT KNOW PRECISELY WHAT CAUSED THE FAILURE BUT BELIEVES AN ELECTRICAL SHORT CIRCUIT OF SOME SORT WAS INVOLVED. STATIC THAT WAS HEARD IN THE HEADSET PRIOR TO THE FAILURE COMPLETELY WENT AWAY ONCE THE MCP FAILED. SUPPLEMENTAL INFO FROM ACN 801309: WHILE ENRTE (FL260); JUST BEFORE TOP OF DSCNT; WE REALIZED THAT THE MCP HAD FROZEN EXCEPT THE COURSE SELECTOR ON MY SIDE. THE AUTOPLT; AUTOTHROTTLES AND FLT DIRECTORS DISENGAGED ON THEIR OWN. AT ZZZ THE ILS HAD THE GS OTS AND WX WAS RIGHT AT OR SLIGHTLY BELOW MINIMUMS FOR THE ILS GS OTS NON-PRECISION APCH. THE CAPT DECIDED THAT WE NEEDED TO FIND AN ALTERNATE WITH BETTER WX. WE WERE INFORMED THAT ACFT HAD JUST ARRIVED AT ZZZ1 UNDER VFR CONDITIONS 6000 FT CEILINGS AND 15 MI VISIBILITY. DUE TO THE GREATLY REDUCED NAV ABILITIES OF OUR AIRPLANE; ZZZ1 WAS THE MOST PRUDENT AND TIMELY ALTERNATIVE. AN EMER WAS DECLARED; WE THEN PROCEEDED DIRECT TO VOR AND SET UP FOR THE LDA DME. WE FLEW THE APCH WITH THE DME ARC TRANSITION AND BROKE INTO THE VFR CONDITIONS AND PROCEEDED ON THE APCH TO THE ARPT AND LANDED WITHOUT FURTHER INCIDENT. I DON'T THINK THAT AN MCP FAILURE CAN BE AVOIDED OR FORESEEN; BUT MORE TIME DURING TRAINING COULD BE SPENT FLYING RAW DATA WITHOUT AUTOPLT; FLT DIRECTORS AND RNP APCHS. WE WERE ALSO NOT ABLE TO FIND ANY REF TO AN MCP FAILURE IN THE QRH.

Data retrieved from NASA's ASRS site as of May 2009 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.