C172 WITH ELECTRICAL DIFFICULTIES DECIDES TO RETURN TO POINT OF ORIGIN. LANDS STP WITH ELECTRICAL FAILURE.

Narrative

THE ACFT BEGAN TO SUFFER ELECTRICAL PROBS ABOUT 2/3 OF THE WAY TO DEST. THIS WAS FOLLOWED BY MARGINAL WX; WHICH FORCED THE RETURN TO ORIGINAL ARPT OR ALTERNATE ARPT. THE DECISION WAS MADE TO RETURN (IF POSSIBLE) TO ORIGINAL ARPT BECAUSE OF SVCS AVAILABLE THERE; IN THE EVENT EMER SVCS WOULD BE NEEDED. ULTIMATELY A COMPLETE FAILURE OF THE ALTERNATOR LED TO CONSERVATION OF BATTERY PWR. ALL NON ESSENTIAL ELECTRICAL EQUIP WAS TURNED OFF. VISIBILITY WAS REDUCED BY HAZE AND SETTING SUN. JUST OUTSIDE CLASS B AIRSPACE I WAS ABLE TO CONTACT ST PAUL TWR; AND INFORM THEM OF MY SIT. I WAS GIVEN A SQUAWK CODE FOR MSP APCH TO MONITOR MY POS. RADIO COM WAS DIFFICULT; AND DURING LNDG; BECAME NON EXISTENT. IN TRYING TO NAV AND LISTEN TO ATC; AND MOST IMPORTANTLY KEEP A SAFE ALT; IT IS POSSIBLE THAT I MAY HAVE ENTERED CLASS B AIRSPACE WITHOUT CLRNC. ALTHOUGH AT NO TIME DID I WITNESS ACTUALLY ENTERING CLASS B AIRSPACE; BUT DID OBSERVE OPERATING CLOSE TO IT. THE ACFT LANDED SAFELY; UPON RECEIVING CLRNC TO LAND VIA LIGHT-GUN SIGNALS. I THANKED THE TWR PERSONNEL VIA TELEPHONE AFTER ENG SHUTDOWN. NO MENTION WAS MADE OF ANY AIRSPACE VIOLATION. THE FBO WAS NOTIFIED OF THE ACFT FAILURE.