C172 instructor pilot reported noting smoke coming from the master switch area and turned off the ma...

Narrative:

In the practice area; I noticed my radio coming in and out. Trouble shooting the issue I noticed that smoke was coming from the master switch area. I turned the master switch off. The cockpit did have a lot of smoke so I ventilated the aircraft. After ensuring all switches were turned off and checking the circuit breakers; I tried engaging the master switch. Immediately smoke was generating again; so I turned the master switch off again. Communication with ATC was not possible with the com radio and transponder. I proceeded northbound on the published arrival and was looking for light gun signals from the tower. After arriving at the downwind for 27L; I still did not see any signal. I assumed they saw me and checked vigorously for traffic before descending from 1500 to traffic pattern altitude. After landing; it came to me that I had a cell phone and possibly could have found reception at a lower altitude; but I was more focused on the airplane and the best navigation possible for ATC and traffic. After landing I called tower as I still could not see any light gun signals. I got in touch with ground control via my cell; and received progressive taxi on the ground. The student in the back seat did say that he saw a flashing white light from tower while I was calling; but I did not see that signal.I forgot that I had ATC programmed on my cell phone. Perhaps I could have checked for cell reception before beginning my approach.

Original NASA ASRS Text

Title: C172 Instructor pilot reported noting smoke coming from the master switch area and turned off the master switch. When the smoke dissipated the switch was turned back on with the same result. The training flight returned to the departure airport using lost comm procedures.

Narrative: In the practice area; I noticed my radio coming in and out. Trouble shooting the issue I noticed that smoke was coming from the master switch area. I turned the master switch off. The cockpit did have a lot of smoke so I ventilated the aircraft. After ensuring all switches were turned off and checking the circuit breakers; I tried engaging the master switch. Immediately smoke was generating again; so I turned the master switch off again. Communication with ATC was not possible with the com radio and transponder. I proceeded northbound on the published Arrival and was looking for light gun signals from the tower. After arriving at the downwind for 27L; I still did not see any signal. I assumed they saw me and checked vigorously for traffic before descending from 1500 to Traffic Pattern Altitude. After landing; it came to me that I had a cell phone and possibly could have found reception at a lower altitude; but I was more focused on the airplane and the best navigation possible for ATC and Traffic. After landing I called Tower as I still could not see any light gun signals. I got in touch with ground control via my cell; and received progressive taxi on the ground. The student in the back seat did say that he saw a flashing white light from tower while I was calling; but I did not see that signal.I forgot that I had ATC programmed on my cell phone. Perhaps I could have checked for cell reception before beginning my approach.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1411473
Time
Date	201612
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Component
Aircraft Component	Electrical Wiring & Connectors
Person 1
Function	Instructor Pilot Flying
Qualification	Flight Crew Commercial Flight Crew Flight Instructor
Events
Anomaly	Aircraft Equipment Problem Less Severe Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor

C172 instructor pilot reported noting smoke coming from the master switch area and turned off the master switch. When the smoke dissipated the switch was turned back on with the same result. The training flight returned to the departure airport using lost comm procedures.