The International Cessna^® 170 Association

For the last few weeks my radio has been making fluttering noises once I try to use my mic. I start my engine, roll out to the ramp, get my ATIS, and then when I call the tower I get a fluttering noise when I talk through the radio as I hold down the mic button. I would compare the noise to a loud beetle flying an inch away from my ear fluttering its wings.

I wait for a response from the tower, no answer. I make my call again with the fluttering noise. no answer. I flip the avionics switch on and off once. No noise during my radio call, response from the tower comes through. This problem has progressively gotten worse and worse to the point where I might have to make four of five attempts by flipping the avionics switch on and off. Once I am in flight/get the fluttering to stop it does not come back for the remainder of the flight. It only occurs at the beginning of each flight when the engine is turned on.

I have checked under the panel for any wires touching each other, loose wires, broken wires etc. and I have not found anything that looks to be out of place. Everything is aligned and tight. I REALLY don't want to take off the piano switches unless I have to. I'm ready to go through that, but I wanted to hear some other opinions from first.

Any input is greatly appreciated!

Chris Hartis
1948 Cessna 170 N2675V
Felts Field, WA KSFF

Which audio/intercom unit do you have? The mic relay which switches between txmt/recv might be failing to reset until power is removed/reapplied.

My PS-Engineering 1000 went thru a goofy/similar failure mode which PS-Engineering claimed was an impossible failure... that their unit would fall-back into a "fail safe" mode...that it MUST be my transmitter. I sent my Com radio back to the mfr'r who could not duplicate the problem ($120-cost) and told me in no uncertain terms that despite the audio/intercom mfr's claim, that the audio/intercom must be the failure. I then sent it to PS-Engineering, who confirmed their problem, made the repair along with another unauthorized modification* in addition to the repair and charged me $100 plus freight.


*PS Engineering removed the side-tone over-ride feature which I did not request.

I have an external intercom that is not built into the panel. The unit is a two place flightcom. Update on the situation is that I messed with some wires (moved them around, made sure all connections were tight) and the problem was fixed for my next three flights. Last night, the problem came back as I made my first call to ground control. I am going to try leaving on my avionics switch when I shut down the plane, and only turn off the master switch when it's time to park. This should hopefully tell me if the problem lies with my avionics switch or with one of my connections.

Thoughts?

Chris, it's generally considered poor practice to start or shut down the engine with the avionics on due to the electrical system surges which accompany those actions. I'd hate for you to suffer an expensive avionics failure due to that, and I cannot see how that procedure will test for a fault.

Can you operate your com radio without the audio/flightcom ? That may isolate it to the flightcom...