Narrative:

The situation occurred whilst on final for the GPS xx approach. The first indication of abnormality occurred shortly before crossing the FAF when the GNS 530; mode south transponder; and HSI abruptly failed. Approach control advised that altitude encoding was lost. Seconds later all electrical power was lost; resulting in failure of the GNS 430; turn coordinator; and digital tachometer. My instructor assumed control of the aircraft; immediately initiating a climbing right turn to an approximately magnetic heading of 270 degrees and an altitude of between 4300-4700 ft MSL; our last known VFR on top altitude. I then contacted TRACON with a cellular telephone and apprised the controller of our plight before losing reception. My instructor concurrently discovered the ammeter indicated zero. After evaluating the situation; we decided our best option was to head toward the last known VFR conditions; thus we initiated a turn towards a southeast heading. Shortly after commencing the turn; sufficient charge accumulated to operate the GNS 430 and permit radio communication. Approach then provided radar vectors through the clouds. We broke out at approximately 900 ft MSL and 1 SM from the threshold and landed without incident. Subsequent pilot inspection of the aircraft revealed the alternator belt was missing. We estimate the belt must have been lost inside class B airspace.

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Original NASA ASRS Text

Title: PA28 LOST ELECTRICAL POWER IN INSTRUMENT CONDITIONS. FLT RETURNED TO VMC; AND BRIEFLY REESTABLISHED RADIO CONTACT FOR VECTORS THROUGH THE CLOUDS FOR AN APCH AND LNDG.

Narrative: THE SITUATION OCCURRED WHILST ON FINAL FOR THE GPS XX APCH. THE FIRST INDICATION OF ABNORMALITY OCCURRED SHORTLY BEFORE XING THE FAF WHEN THE GNS 530; MODE S XPONDER; AND HSI ABRUPTLY FAILED. APCH CTL ADVISED THAT ALT ENCODING WAS LOST. SECONDS LATER ALL ELECTRICAL PWR WAS LOST; RESULTING IN FAILURE OF THE GNS 430; TURN COORDINATOR; AND DIGITAL TACHOMETER. MY INSTRUCTOR ASSUMED CTL OF THE ACFT; IMMEDIATELY INITIATING A CLBING R TURN TO AN APPROX MAGNETIC HDG OF 270 DEGS AND AN ALT OF BTWN 4300-4700 FT MSL; OUR LAST KNOWN VFR ON TOP ALT. I THEN CONTACTED TRACON WITH A CELLULAR TELEPHONE AND APPRISED THE CTLR OF OUR PLIGHT BEFORE LOSING RECEPTION. MY INSTRUCTOR CONCURRENTLY DISCOVERED THE AMMETER INDICATED ZERO. AFTER EVALUATING THE SITUATION; WE DECIDED OUR BEST OPTION WAS TO HEAD TOWARD THE LAST KNOWN VFR CONDITIONS; THUS WE INITIATED A TURN TOWARDS A SE HDG. SHORTLY AFTER COMMENCING THE TURN; SUFFICIENT CHARGE ACCUMULATED TO OPERATE THE GNS 430 AND PERMIT RADIO COM. APCH THEN PROVIDED RADAR VECTORS THROUGH THE CLOUDS. WE BROKE OUT AT APPROX 900 FT MSL AND 1 SM FROM THE THRESHOLD AND LANDED WITHOUT INCIDENT. SUBSEQUENT PLT INSPECTION OF THE ACFT REVEALED THE ALTERNATOR BELT WAS MISSING. WE ESTIMATE THE BELT MUST HAVE BEEN LOST INSIDE CLASS B AIRSPACE.

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.