PA-30 Twin Comanche
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 8; Flight Crew Total 5600; Flight Crew Type 400
Aircraft Equipment Problem Less Severe
Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport
Aircraft
Unnoticed electrical issue with both alternators falling offline and battery draining without a discharge indication on the single ammeter. After release from flight following; switched to UNICOM for ZZZ. While enroute had noticed several indicators of electrical issue beginning but misinterpreted as flight control issues. Autopilot dropped offline. Electric trim then went inoperative. As the gear was lowered entering the pattern; all radios and other electrical equipment dropped offline and gear stopped in an intermediate position. Cycled alternators and battery. Able to retract but not extend the gear. Would pop the CB on each extension attempt. Cycled alternators again and saw a large 50 amp draw by the battery on ammeter. Circled the airport a bit and determined battery charging by the drop in amps on ammeter. Decided to fly long enough to re-charge battery before trying to lower gear again electrically. Decided to Return to Base (RTB). More familiar airport. Unable to raise anyone on UNICOM before losing radios; so not sure if any support/equipment would be available. Flew direct line via visual references. Potentially passed through cold Military Operating Areas (at least they were cold on the way over) and remained just outside the edge of the Class D airspace. Once battery appeared re-charged; cycled CB for alternators and gear. All electrical systems appeared normal. Normal gear extension. Normal approach and landing with no further issues.
A PA-30 pilot reported his battery was drained when both alternators dropped off line. He reset the alternators and returned to the departure airport; flying long enough to charge the battery for landing gear extension.