Narrative:

The aircraft began to suffer electrical problems about 2/3 of the way to destination. This was followed by marginal WX, which forced the return to original airport or alternate airport. The decision was made to return (if possible) to original airport because of services available there, in the event emergency services would be needed. Ultimately a complete failure of the alternator led to conservation of battery power. All non essential electrical equipment was turned off. Visibility was reduced by haze and setting sun. Just outside class B airspace I was able to contact st paul tower, and inform them of my situation. I was given a squawk code for msp approach to monitor my position. Radio communication was difficult, and during landing, became non existent. In trying to navigation and listen to ATC, and most importantly keep a safe altitude, it is possible that I may have entered class B airspace without clearance. Although at no time did I witness actually entering class B airspace, but did observe operating close to it. The aircraft landed safely, upon receiving clearance to land via light-gun signals. I thanked the tower personnel via telephone after engine shutdown. No mention was made of any airspace violation. The FBO was notified of the aircraft failure.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 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.