Narrative:

I was flying right seat in a cessna 172 as PIC/pilot not flying; the departure airport was IMC. I filed two IFR flight plans. The first leg was for a planned fuel stop. I received a full briefing and picked up an IFR clearance. Included in the briefing was a pilot report of tops at 2;000 with conditions improving along the route. We were cleared to 6;000 and flew V1. At approximately 15 DME from approach advised us that they were getting unreliable altitude readouts from our transponder and ask us to turn off mode C. At about this time I noticed a red annunciator light on; indicating that the alternator was off line. The 50 amp main breaker was popped and I recycled it. The breaker remained in for a few minutes and then popped again. At this point I shed all non essential electric and used only com 1 and transponder. I advised approach of our situation and told them our intention was to continue on our route and I would advise. We were handed over to the next approach control. At this point conditions were VMC. After remaining with the next approach control for about 10 minutes my radios began to get weak. I told the controller that I was going to cancel IFR and land as soon as practical. The controller handed me off to another approach facility and I informed approach that I intended to land. Approach accepted my cancellation and I landed without incident. As fortune would have it; there was a mechanic on duty. He checked over the aircraft and could not find any abnormality. He asked if I had recycled the alternator and I told him that I had not. After checking under the cowl and the instrument panel; we recharged the battery and I was advised by the mechanic that the problem was most likely an overload. We reset the breaker; started the engine and all seemed normal. After refueling we set out VFR. Our intended route was EMI; fdk direct. Approximately 20 minutes after takeoff we experienced the same malfunction as earlier. At this point we were not in touch with ATC and were not on a flight plan. I attempted to contact potomac approach but was unable. The radio grew weaker and subsequently lost power. From this point on we were flying by dead reckoning using the washington sectional for navigation. I was aware of the washington sfra; but also concerned not to near or enter P-40/R4009. With the sun setting and no electrical power I felt we would not have time to reach our destination. While looking for a suitable alternate; I navigated what I believed was north of the washington sfra yet clear of camp david. We located and agreed upon ZZZ as our alternate. The airport is east of the mostly mountainous terrain; well clear of restricted airspace and within range to land while still daylight. We over flew ZZZ to check for traffic; circled north and landed to the east. After landing a gentleman; the airport manager; rode out to our plane on a bicycle and informed us that potomac TRACON wanted us to give them a call. I called potomac and was told that I had crossed into washington sfra without authorization. I explained to the controller that if I had entered restricted airspace it was inadvertent. Apparently he was aware that we were having some sort of electrical problem. The controller informed me that a report would be filed and that I should expect to hear from the FAA concerning this incident. At no time did I intentionally enter into restricted airspace. I am familiar with dca sfra and understand its importance to our national security. If I did cross into the sfra; I am certain that it was by a very small margin. Though this is not an excuse; it is an explanation that entry was completely unintentional.

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Original NASA ASRS Text

Title: C172 pilot experiences an alternator failure on an IFR flight plan in VMC and diverts for maintenance. No anomalies can be detected by maintenance and the flight is continued; with a second failure occurring 20 minutes into flight. With no NAV or COMM an inadvertent DCA SFRA incursion occurs before landing at an airport outside the SFRA.

Narrative: I was flying right seat in a Cessna 172 as PIC/pilot not flying; the departure airport was IMC. I filed two IFR flight plans. The first leg was for a planned fuel stop. I received a full briefing and picked up an IFR clearance. Included in the briefing was a pilot report of tops at 2;000 with conditions improving along the route. We were cleared to 6;000 and flew V1. At approximately 15 DME from Approach advised us that they were getting unreliable altitude readouts from our transponder and ask us to turn off mode C. At about this time I noticed a red annunciator light on; indicating that the alternator was off line. The 50 amp main breaker was popped and I recycled it. The breaker remained in for a few minutes and then popped again. At this point I shed all non essential electric and used only com 1 and transponder. I advised Approach of our situation and told them our intention was to continue on our route and I would advise. We were handed over to the next Approach Control. At this point conditions were VMC. After remaining with the next Approach Control for about 10 minutes my radios began to get weak. I told the Controller that I was going to cancel IFR and land as soon as practical. The Controller handed me off to another Approach facility and I informed Approach that I intended to land. Approach accepted my cancellation and I landed without incident. As fortune would have it; there was a mechanic on duty. He checked over the aircraft and could not find any abnormality. He asked if I had recycled the alternator and I told him that I had not. After checking under the cowl and the instrument panel; we recharged the battery and I was advised by the mechanic that the problem was most likely an overload. We reset the breaker; started the engine and all seemed normal. After refueling we set out VFR. Our intended route was EMI; FDK direct. Approximately 20 minutes after takeoff we experienced the same malfunction as earlier. At this point we were not in touch with ATC and were not on a flight plan. I attempted to contact Potomac Approach but was unable. The radio grew weaker and subsequently lost power. From this point on we were flying by dead reckoning using the Washington sectional for navigation. I was aware of the Washington SFRA; but also concerned not to near or enter P-40/R4009. With the sun setting and no electrical power I felt we would not have time to reach our destination. While looking for a suitable alternate; I navigated what I believed was north of the Washington SFRA yet clear of Camp David. We located and agreed upon ZZZ as our alternate. The airport is east of the mostly mountainous terrain; well clear of restricted airspace and within range to land while still daylight. We over flew ZZZ to check for traffic; circled north and landed to the east. After landing a gentleman; the airport manager; rode out to our plane on a bicycle and informed us that Potomac TRACON wanted us to give them a call. I called Potomac and was told that I had crossed into Washington SFRA without authorization. I explained to the Controller that if I had entered restricted airspace it was inadvertent. Apparently he was aware that we were having some sort of electrical problem. The Controller informed me that a report would be filed and that I should expect to hear from the FAA concerning this incident. At no time did I intentionally enter into restricted airspace. I am familiar with DCA SFRA and understand its importance to our national security. If I did cross into the SFRA; I am certain that it was by a very small margin. Though this is not an excuse; it is an explanation that entry was completely unintentional.

Data retrieved from NASA's ASRS site as of July 2013 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.