Cessna 337 Super Skymaster
Flight Crew Multiengine; Flight Crew Private
Flight Crew Last 90 Days 9; Flight Crew Total 753; Flight Crew Type 557
Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft
The flight was normal and uneventful from ZZZ to ZZZ1. I was flying VFR under a flight plan and preparing for arrival to ZZZ1. I received ATIS information Gulf; which advised to use XXX.X to contact the Tower; and that the XXX.Y frequency was inoperative. I contacted ZZZ1 Tower over [waypoint]; confirmed [ATIS] information Gulf and Controller instructions to fly over [the] dam and extend base to [Runway] XXL. About this time; I activated landing lights. Subsequently; I heard the Tower instruction that I may shorten my pattern as another aircraft had exited and was cleared for landing. I acknowledged (however I subsequently learned that the Tower was not receiving my transmissions). During this time; I set the landing gear down and was preparing for the pattern turn. On approximately 2 mile final; I had a perception that the instrument lights were dimming; but still operating. I was completing a pre-landing GUMP and was unable to identify my landing gear completion cycle 'green light' indicator. I quickly looked out the window to confirm main gear extension; but unable to see the nose gear.  The flaps extension did not activate; and upon consideration; I elected to perform a go-around. I transmitted to the Tower advising that 'I had not received gear down confirmation and was performing a go-around to recycle the gear' but did not receive a reply (as mentioned above; Tower was not receiving my transmissions and I was unaware of this at the time). About this same time; all instrument panel lights and radios went dark; gauges dropped to null readings; and I could see the landing lights were not functioning. It was clear during the power-up stage of the go-around that I had suffered a complete electrical failure. I activated a flashlight in the cabin; established a left pattern return to [Runway] XXL; performed a series of procedures to investigate for fire; shorts; alternator and circuit breaker problems and de-load the system; while deliberating over the landing gear issue. During this time I looked for and saw a green light from the Tower and focused attention on completing the landing of the aircraft. The gear lock indicator was in place and I felt the gear light may be related to the rest of the electrical; so I proceeded with the landing procedure while still attempting to recover electric power. After searching the landing patterns and extending due to seeing one set of position lights from another aircraft in the vicinity; I re-established final approach when clear. During final; I saw green lights flashing from the Tower area and proceeded; I then noticed red flashing lights in the vicinity of the Tower and prepared for another go-around until I was able to determine that these were emanating from emergency vehicles. Flaps were still inoperative; and I performed a normal landing. Upon exiting the runway I was assisted by an emergency vehicle that helped illuminate the pathway out of the movement area and back to parking. Although it appeared one of the radios was attempting to fire back up just as I was shutting down the aircraft; I have not yet determined what precisely happened with the electrical system. Subsequent to shut-down; I spoke with the Fire Crew who assisted us and contacted the Tower Controller to explain what occurred. I believe all personnel acted in a very professional manner that was appropriate for the situation and was sure glad they were there in this event. Upon consideration and review of the incident with my mechanic; and considering the 'Chain of Events' and 'Human Performance Considerations;' I believe that a more aggressive observation of the electrical signals may have been helpful in either heading off this result; or at least communicating it before the radios went dead. As mentioned above; I did notice a dimming of the lights. The Skymaster is 1966 vintage and uses post lights on the panel which are relatively dim compared to newer systems. Thus; a certain 'I'm used to this' attitudemay need to be adjusted; because they seemed to be unusually dimming at the end of the flight. Had this occurred midway through the flight; I may have had more time to troubleshoot; but it was lighter ambient conditions; and that may have masked the situation further (my newer radios automatically darken as the skies darken). I believe that the battery of the aircraft may have become discharged to a point that the electrical system was overwhelmed. But I also feel this must have been compounded by the failure of the alternator(s) to pick up the difference. I still have some questions on that. The low voltage light never illuminated and I always check circuit breakers before starting engines and during the run-up. I usually check circuit breakers between decent and arrival procedure as well and on this particular flight; I checked them again during the go-around. I did not notice any abnormality; but at shut-down the rear alternator was popped. The airplane has a front alternator; we're still not sure why that didn't seem to pick up the difference; but I am told that it is possible the battery may not have had enough charge to excite the field coil to energize the alternator. This also perplexes me as the engines started on battery power. However; I did have prior legs on the day's flight and this required an abnormally long hot start at a high altitude location which I am much more interested in now than at the time. Could the battery have somehow drained below the needed level but still cranked the engine?  Since the flight; we pulled the battery and it indicated dead on testing. The mechanic recharged it; load tested it; and re-certified it for operation. Connections were double checked and cleaned and I have since tested all electrical items; verified both over volt and undervolt warning lights; gear lights; battery and charging indicators; and subjected the electrical system to a full load of use and unable to recreate the situation (starting with a known full charge battery; of course). So this is still a bit of a mystery; but I am moving battery condition to a higher priority than I previously did.  The last item that I think was sort of unexpected but may deserve some attention is the location and status of emergency vehicles in the vicinity of the tower at night. During the final approach after going around; the flashing red lights in the proximity of the Tower; with my completely dark cockpit and the somewhat distracting flashlight use; resulted in my momentary belief that the green light signal had changed and that I was to go around again. My cowl flaps are electric; and [the city] was over 105 degrees Fahrenheit that evening and the thought of another go around with dead electric (and possible complications or reason why) and possible heating up engines (it's amazing what goes through the mind during these moments) caused me a bit of dread until I determined it was fire trucks. I'm actually very happy with the response of the emergency procedures and can't rave enough how glad I was they were there; but it may be helpful; at night conditions; to use yellow or blue lights instead of red ones on emergency vehicles near the Tower - in the event the airplane has no radio. As I read this; that may be too limited an event; but it was a [momentary] link in the chain.
C337 pilot reported electrical power failure resulting in a precautionary landing at night.