FLC OF AN DH-8 ACR ACFT DECLARED AN EMER AND DIVERTED TO LAND DUE TO A FAILURE OF THE L GENERATOR CTL UNIT AND THE ELECTRONIC LOGIC AND MONITORING UNITS.

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THE ACFT WAS A DHC-8-102 WITH NO MEL OR CDL ITEMS. THE WX WAS VFR OVER THE RTE OF FLT INCLUDING TRI AND DTW. AT APPROX XX40Z AT 19000 FT; THE L SIDE (CAPT'S) FLT DIRECTOR; AND DME FAILED. THE DME FAILURE ALSO CAUSED THE LOSS OF THE R-NAV; AND ATC WAS ADVISED. WITHIN 5 MINS; THE L FLT INSTS AND PARTIAL ENG INSTS BEGAN TO FAIL. ACFT CTL WAS TRANSFERRED TO THE COPLT; AND QRH (ABNORMAL CHKLIST) PROCS WERE FOLLOWED. DURING QRH PROCS; NUMEROUS L SIDE SYS BEGAN TO FAIL (INDICATED BY CAUTION LIGHTS). IT WAS APPARENT THAT THERE WAS A PROB WITH THE L ELECTRICAL DISTRIBUTION SYS. HOWEVER; THE NORMAL FAULT LIGHTS WERE NOT ILLUMINATED; AND THE INVERTER LOAD DISPLAY READINGS WERE NORMAL. CABIN PRESSURIZATION ALSO FAILED RESULTING IN LOSS OF CABIN PRESSURE. AUTO CABIN TEMP FAILED REVERTING TO UNCTLABLE FULL HOT SETTING. ATC WAS ADVISED OF THE NEED FOR IMMEDIATE DSCNT TO A LOWER ALT. QRH PROCS IMMEDIATELY FOLLOWED; BUT WERE INTERRUPTED BY ADDITIONAL SYS CAUTION LIGHTS; AND CABIN AND CARGO DOOR WARNING LIGHTS. DUE TO THE MULTIPLE AND UNRELATED FAILURES OCCURRING WITHIN MINS OF EACH OTHER; IT WAS MUTUALLY DECIDED TO DECLARE AN EMER. ATC PROVIDED VECTORS TO THE NEAREST ARPT-MANSFIELD LAHM (MFD); MANSFIELD; OH. MFD ARPT WAS 18 MI AWAY UNDER VFR CONDITIONS. THE FLT ATTENDANT AND COMPANY DISPATCH WERE NOTIFIED. NORMAL AND QRH CHKLISTS WERE COMPLETED. A NORMAL LNDG FOLLOWED WITHOUT INCIDENT. COMPANY MECHS LATER DISCOVERED THE L GENERATOR CTL UNIT; AN ELECTRONIC LOGIC AND MONITORING UNIT HAD FAILED. THIS FAILURE ALLOWED A FAULTY GENERATOR TO PROVIDE 'WILD' CURRENT TO SHORT-OUT THE L ELECTRICAL DISTRIBUTION SYS. NORMAL CAUTION LIGHTS FOR THIS SIT (INCLUDING THE L GENERATOR CAUTION LIGHT) NEVER ILLUMINATED DUE TO THE LOSS OF SYS LOGIC. THE END RESULT MASKED THE ACTUAL PROB. CREW COORD WAS ESPECIALLY GOOD CONSIDERING THE CONFUSION AS TO WHAT WAS CAUSING THE FAILURE AND HOW TO BEST DEAL WITH THE SIT. THE CREW ALSO HAD TO PRIORITIZE MULTIPLE FAILURES; SOME OF WHICH DID NOT HAVE A QRH CHKLIST. THE CREW HAD A LIMITED AMOUNT OF TIME TO COMPLETE THE CHKLISTS DUE TO THE SHORT DISTANCE TO MFD ARPT (18 MI FROM POINT OF DIVERSION). CONSIDERING THE IMPORTANCE OF THE GCU IN THE DHC-8; IT WOULD APPEAR THAT FAULT SENSING OF THE GCU SHOULD BE INCORPORATED INTO THE CAUTION ADVISORY PANEL.