Duchess 76
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft
We were doing a planned Engine Shutdown as part of the lesson. After student successfully shut down the left engine and feathered the prop using his checklist; he started to execute the Engine Secure Checklist as discussed and briefed from before. Me as the instructor; I noticed that the intercoms were not functioning. I was unable to hear or talk to my student nor to the passenger in the backseat which was also another student observing. I checked my headset jacks to make sure they were plugged in correctly. But that didn't solve the issue. At that point I also started to smell smoke (no visible smoke). I started to look at the instruments and equipment on board and I noticed the following: ISO BUS 2 circuit breaker popped out and the right load meter was indicating zero load and the under voltage light was on for the right alternator. At that point I knew that it was too much load on the right alternator and that it shut down. I tried to reset the ISO BUS 2 circuit breaker by pushing it in twice but it wouldn't stay in. So I left it alone and started to shut down unnecessary electrical items (Fuel pumps and lights). I took control from my student and started turning towards the airport squawked 7600 hoping that we can restart our avionics. After 2 minutes I tried to reset it one last time; it worked and I was able to restart all comms and avionics. I immediately started our descent from 4;500 feet and contacted tower and I told tower that we might lose radio comms any minute. Tower gave us a straight in which was perfect for our Altitude and position and not too long after; cleared us to land. After landing safely I was able to taxi back to the ramp without any issues. I grounded the airplane.
BE76 instructor reports loss of electrical power and electrical fumes after shutting down the left engine during a training flight. The ISO Bus 2 circuit breaker is found tripped and two reset attempts are unsuccessful. Nonessential electrical equipment is shut down and the aircraft is turned toward the home airport. After two minutes; a third attempt to reset the circuit breaker is successful and a landing ensues.