Renegade Warning Horn

[chopperboy]

I wrote here not long ago about a turbo problem that I just got fixed from the wonderful, friendly folks at Main Turbo. But, now I have a new problem. I picked up the airplane for the flight home. Liftoff, gear up, turning on course and a warning horn alerts. Nothing out of the ordinary showing, annunciator lights dark, can't figure it out. Proceed 10 minutes to home base with horn blaring. Pre-landing check is fine, including gear down and locked. Then on short final horn gradually gets weaker and then goes off completely. Check out everything on the ground, taxi back and take off again to see if it comes back on. Same exact scenario from start to finish. Taxi to the ramp with no horn, cool off and shut down. Next day trying to troubleshoot, turn on master and horn comes on. No radios on, just master. Start pulling breakers and find a combination of pulling the gear warning and stall warning breakers silences the horn. Push in one or the other and the horn sounds. With both pulled it's off. I'm figuring both warnings use the same horn because it sounded the same regardless of which of the two breakers I pushed in.

 

Ever heard of this before? Any ideas? Appreciate any help I can get.

 

Thanks!

[Hank]

I had a horn sounding after annual this year with a new a&p. Pulling breakers isolated the stall horn.

Shut down to discuss, he had washed the plane while I was driving over to pick it up. We could manually raise the stall indicator and it would get much louder; release it and volume would decrease; press gently and it would stop; let go and it would start again.

It was disconcerting to hear a horn as soon as I turned on the master switch. A few days later, all dry and no more horn sounding.

[Piloto]

Flip the stall vane at leading edge several times to see if it makes a difference. It may just need some WD-40.

José

[N201MKTurbo]

On my J, it is possible for the terminals on the sonoalert to short on the fuselage causing the horn to sound. If it does it again flick the horn with your finger and see if it changes it. If it does then re-do the insulation on the terminals and put some tape or cardboard on the bare metal above the horns.

[N201MKTurbo]

I had a horn sounding after annual this year with a new a&p. Pulling breakers isolated the stall horn.

Shut down to discuss, he had washed the plane while I was driving over to pick it up. We could manually raise the stall indicator and it would get much louder; release it and volume would decrease; press gently and it would stop; let go and it would start again.

It was disconcerting to hear a horn as soon as I turned on the master switch. A few days later, all dry and no more horn sounding.

 

That's why I always fly the plane after washing it. It blows all the water out of everything. I've had that happen before, a half a lap around the pattern usually makes it go away. 

[chopperboy]

Okay... had already tried flipping the stall vane and no change. Plus... this happens with the gear warning as well... stall and gear warnings share the same horn, correct?

 

Thanks again guys.

[Marauder]

Okay... had already tried flipping the stall vane and no change. Plus... this happens with the gear warning as well... stall and gear warnings share the same horn, correct?

Thanks again guys.

Not sure what model you have, but no, the Sonalerts are two different ones. I think if you have an older C/E or F model there was a different style. Mine are in the overhead area.

[firefly201]

Chopperboy, page 7-23 of your POH circuit breaker diagram. Shows two breakers on a M20M, Gear and stall

[Tommy]

I had almost an identical problem - now fixed - as yours.

 

Try this

 

1) Make sure you turn eletric trim off because the trim warning will sound if you turn master on without turning on the avionics switch.

2) Now turn on the master, if you have hear something blaring then proceed to pull the stall warning CB. If the sound stops then you have got a short in your stall warning circuit. If it doesn't, the proceed to pull the gear warning CB off. It the sound then stops, you have got a short in your gear warning circuit.

 

Pretty simply to diagnose.

 

The fun part is to hunt down the short. In my J it was a wire between the CB and the canon plug that goes out to the stall warning vane, which is good because I don't need to take down the overhead panels or replacing a broken stall warning vane ($1500!!!)

 

Good luck.

[chopperboy]

Hey Tommy -

 

Thanks for the input. Tried switching off electric trim, but still have same problem. Here's the weird part that I'm not sure everyone has understood. With both gear and stall warning breakers pulled, horn is off. With either pushed in the horn sounds. However, contrary to what some have written here, it sounds like the exact same horn. A couple of the guys have suggested that there are two separate horns, one for each. However, if I have both breakers pushed in with the horn sounding, and I pull one or the other, there is absolutely no change in the sound of the horn. No pitch change, no volume change, notta... zilch. So there is either a single horn common to both, or the issue is pushing either breaker sounds one of the two separate horns.

 

As they say... go figure! Thanks again....

 

Anybody else want to chime in?

[JaredDavis]

Long shot:  Do you have a voice alert installed?  I have a EI AV-17 hooked to my gear and stall warning horns. After some slow flight practice the stall horn would not stop blaring.  When the AV-17 was disconnected, the horn would stop.  Sent the AV-17 in for repair to resolve the issue. 

[M20S Driver]

Hey Tommy -

 

Thanks for the input. Tried switching off electric trim, but still have same problem. Here's the weird part that I'm not sure everyone has understood. With both gear and stall warning breakers pulled, horn is off. With either pushed in the horn sounds. However, contrary to what some have written here, it sounds like the exact same horn. A couple of the guys have suggested that there are two separate horns, one for each. However, if I have both breakers pushed in with the horn sounding, and I pull one or the other, there is absolutely no change in the sound of the horn. No pitch change, no volume change, notta... zilch. So there is either a single horn common to both, or the issue is pushing either breaker sounds one of the two separate horns.

 

As they say... go figure! Thanks again....

 

Anybody else want to chime in?

 

My  Eagle is exactly the same wiring .  I had a stuck stall switch and I had to pull both gear and stall horn circuit breakers to stop the horn.  

 

The root cause of my problem (Intermittent stall alerts)  was a bad connection in the intercom.  It only happened with the avionics "ON".

[moosebreath]

Same exact problem on my 1996 M20J. The stall vane decided to fail and sound continously after three hours of straight and level flight while over the mountains an hour and a half out of Salt Lake.

I love my Mooney but a horn that loud you can not silence by pulling it's beaker is an incredibly stupid design.