Narrative:

On arrival into ZZZ airport; we were given an ILS (day; 400 ft overcast). We were established on the ILS and fully configured for landing; just before entering IFR conditions we experienced an electrical emergency dc bus failure; which in turn failed the entire left side of panel in cockpit. Once the copilot and I figured out what was happening; we leveled off for a missed approach. It took awhile to verify all failures; so went on runway heading and climbed to 12000 ft. While we tried to figure out what all had failed; we squawked 7600 and identify because initially we had thought we lost all communications: navs. Upon further inspection we had only lost all #1 side (#1 communication; #1 airspeed indicator; #1 altimeter indicator; #1 vsi; #1 navigation; #1 tubes; left side engine gauges). We spoke without headsets about the WX: where to proceed. We decided to proceed to a VFR airport in case the #2 side instruments were erroneous. We proceeded towards ZZZ1. We ran the most important (emergency) checklists and we then saw #2 communication may be working. The copilot tried to reach someone (first time was only static). He was able to hear our flight operations; we told them we had multiple failures in cockpit; we went around and now proceeding to ZZZ1. Please call tower. They were on the phone with them already. We then advised them we had to switch to ZZZ1 approach (we were approximately 50 mi south of ZZZ1). We advised the flight attendant and passenger that we would divert to ZZZ1. Please prepare cabin for an emergency landing. We landed safely in ZZZ1 and we were towed off the runway due to no steering. Callback conversation with reporter revealed the following information: that the emergency dc bus #1 had shorted out and caused other buses to fail. This bus is supposed to remain powered when all others have failed. This EMB120 is a very early example with a somewhat unique electrical system and may have had this problem before.

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Original NASA ASRS Text

Title: EMB120 CREW HAS ELECTRICAL FAILURE ON FINAL APCH AND DIVERTS.

Narrative: ON ARR INTO ZZZ ARPT; WE WERE GIVEN AN ILS (DAY; 400 FT OVCST). WE WERE ESTABLISHED ON THE ILS AND FULLY CONFIGURED FOR LNDG; JUST BEFORE ENTERING IFR CONDITIONS WE EXPERIENCED AN ELECTRICAL EMER DC BUS FAILURE; WHICH IN TURN FAILED THE ENTIRE L SIDE OF PANEL IN COCKPIT. ONCE THE COPLT AND I FIGURED OUT WHAT WAS HAPPENING; WE LEVELED OFF FOR A MISSED APCH. IT TOOK AWHILE TO VERIFY ALL FAILURES; SO WENT ON RWY HDG AND CLBED TO 12000 FT. WHILE WE TRIED TO FIGURE OUT WHAT ALL HAD FAILED; WE SQUAWKED 7600 AND IDENT BECAUSE INITIALLY WE HAD THOUGHT WE LOST ALL COMS: NAVS. UPON FURTHER INSPECTION WE HAD ONLY LOST ALL #1 SIDE (#1 COM; #1 AIRSPD INDICATOR; #1 ALTIMETER INDICATOR; #1 VSI; #1 NAV; #1 TUBES; L SIDE ENG GAUGES). WE SPOKE WITHOUT HEADSETS ABOUT THE WX: WHERE TO PROCEED. WE DECIDED TO PROCEED TO A VFR ARPT IN CASE THE #2 SIDE INSTS WERE ERRONEOUS. WE PROCEEDED TOWARDS ZZZ1. WE RAN THE MOST IMPORTANT (EMER) CHKLISTS AND WE THEN SAW #2 COM MAY BE WORKING. THE COPLT TRIED TO REACH SOMEONE (FIRST TIME WAS ONLY STATIC). HE WAS ABLE TO HEAR OUR FLT OPS; WE TOLD THEM WE HAD MULTIPLE FAILURES IN COCKPIT; WE WENT AROUND AND NOW PROCEEDING TO ZZZ1. PLEASE CALL TWR. THEY WERE ON THE PHONE WITH THEM ALREADY. WE THEN ADVISED THEM WE HAD TO SWITCH TO ZZZ1 APCH (WE WERE APPROX 50 MI S OF ZZZ1). WE ADVISED THE FLT ATTENDANT AND PAX THAT WE WOULD DIVERT TO ZZZ1. PLEASE PREPARE CABIN FOR AN EMER LNDG. WE LANDED SAFELY IN ZZZ1 AND WE WERE TOWED OFF THE RWY DUE TO NO STEERING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THAT THE EMER DC BUS #1 HAD SHORTED OUT AND CAUSED OTHER BUSES TO FAIL. THIS BUS IS SUPPOSED TO REMAIN POWERED WHEN ALL OTHERS HAVE FAILED. THIS EMB120 IS A VERY EARLY EXAMPLE WITH A SOMEWHAT UNIQUE ELECTRICAL SYS AND MAY HAVE HAD THIS PROB BEFORE.

Data retrieved from NASA's ASRS site as of January 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.