Date: 201909
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Skyhawk 172/Cutlass 172
Operator: FBO
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Takeoff / Launch
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Air/Ground Communication
Component problem: Failed
Reporter organization: FBO
Reporter function: Instructor; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Multiengine
Human factors: Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed As Precaution; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: After rotation Runway XX I heard numerous clicking coming from the comms. I was conducting a discovery flight and expected the student had inadvertently activated the com. Neither my student nor I were engaging the transmit button but the [transmitter] was flashing quickly on the Garmin 430 com (aircraft has a PS8000 audio panel and 1 Com/Nav G430). We were around 200 ft. AGL when I realized something had happened with the audio panel that gave me a stuck mic and also prevented me from hearing Tower. I flipped to COM2 in the audio panel to stop blocking Tower frequency; briefed the passengers on what was happening (stuck mic; will need to come around to land) and continued climbing out for a normal pattern. I flipped back to COM 1 to transmit into the blind my intentions (stuck mic; returning left traffic Runway XX).At this point; the coms began behaving normally and I could hear Tower again. Tower confirmed a stuck mic on Ground and Tower and gave me the option of continuing around Runway XX or teardrop for Runway XY (winds 260 at 8). I confirmed teardrop for Runway XY and as I finished the transmission my mic became stuck again. I selected [transmission/receiver] on Com 2 and [receiver] on Com 1 to hear Tower but no transmissions were able to be heard. I executed the teardrop and final for Runway XY received the steady green light for landing. Once landed I asked Tower for permission to roll to D for an exit to the south of the Runway (permission request to be granted with a green light). I received no lights so I exited [taxiway] (north side of the Runway) due to the B737 holding short of Runway XX. On roll out onto [taxiway] I began to hear Tower again and transmitted my intentions to hold short at [taxiway]. After this transmission I again got a hot mic and for the duration of the remainder of the flight/taxi was never able to hear over the coms again. Tower gave me a steady red light to remain where I was until the airport dispatched a vehicle to escort me back to the ramp. Once shut down I reported the failure to Maintenance and reviewed the LIVE ATC logs of Ground and Tower. On review; I found that I had experienced an intermittent hot mic on ground frequency prior to being cleared for taxi and takeoff but was not advised of the issue nor did I notice during taxi (Taxi and Takeoff clearance was received normally; hot mic was during taxi to runup and during runup). Maintenance reported that the audio panel had shorted out during the flight which caused the hot mic.




Synopsis: C172 instructor reported an audio panel failure on takeoff resulting in a return to the airport.