Electrical issue with the stall horn

[Parker_Woodruff]

Here's a gremlin for yall.

 

So I fly over from Lakeland to Albert Whitted (SPG) tonight for dinner with some friends.  Great flight over with the "carrier" landing.  We go in for dinner.  As expected in Florida, a storm passes over and rains a decent amount.  We finish up eating and about 20 minutes later the weather has cleared far enough for me to give the "ok" for departure.

I load up the airplane.  Master switch ON.  Next thing you know the overhead speaker is screeching like none other.  I can't for the life of me think what it might be.  It sounded much too shrill for the stall horn.  It wasn't the autopilot.  No switches changed it.  The landing gear switch was in the down position.

So I get out of the plane, leaving the Master ON  and go activate the stall horn.  Now there are 2 different horns going off in the airplane, so I know that it's not a stuck stall horn.

So I call up Don Maxwell.  He doesn't pick up.  Ken Reed doesn't pick up.  But whaddoyaknow my buddy Gary Hellman (fantom) does.   So now I actually have a pilot on the other side of the phone to talk through this with.  Finally I get the idea to just start pulling circuit breakers to see what stops it.  Sure enough, the STALL HORN circuit breaker ends the noise.

So apparently I now have a stall horn that always stays on, and another that actually comes on when the stall switch is engaged.

Any ideas?

PS: I am back safe in Lakeland.  My passengers heard enough alarms today...but they were troopers.  One had her first ride in ANY airplane.  My buddy Jeff had only been with me once and once in an American Airlines jet.  His girlfriend had never been in a small plane.

[mooniac58]

I am thinking that perhaps another horn shares the breaker with the stall horn.  In my aircraft (87J) the wiring harness is shared for the gear/stall horns - and I don't have a breaker for the gear horn, so my guess would be they might share this breaker?

Unfortunately I cannot easily test this theory in my aircraft on the ground, otherwise I would run down to my hangar to check this for you.

[Parker_Woodruff]

My gear horn is a different sound than this one was making.

[Shadrach]

Do you have a handheld GPS or any other device that is wired to the busbar???

[Parker_Woodruff]

Hey Shadrach,

There is a Garmin 396 powered by the aircraft, mounted on the yoke.

I went flying yesterday and the alarm did not sound at all with the breaker back in.

[FAST FLIGHT OPTIONS LLC]

Could it have been the A/P elevator trim switch (on/off)  buzzer? 

[flyboy0681]

I remember a warning sound when my plane was on the jacks and the gear was being cycled. It was a steady drone, perhaps from the pushing the red override button?

[Parker_Woodruff]

Quote: 201-FLYER

Could it have been the A/P elevator trim switch (on/off)  buzzer? 

[Seth]

Parker-

First off, every time I look at your 252 I want to compliment you on finding a great plane - I looked at your airplane during my current search - it is in good shape - I enjoyed the history of it living in England for a while as well.

Here is a strange event that occured to me:

Fuel pump:  I know this sounds a bit strange, but after flying through a downpour on an extended instrument approach this past May, a burning smell and then high-pitched blaring sound played over my intercom system.  This was not a stall warning sound, but an actuall high pitch squeal thorugh the intercom system.  If you say this noise is coming from your overhead speaker, it may be similar.  Due to the burning smell, I quickly started troubleshooting and when I turned off my aux fuel pump, the sound stopped and soon after the burning smell dissapaited.  I did not turn it back on until on the ground for fear of a potential fire. 

My auxillary fuel pump basically was on it last legs.  It wasn't a ground wire broken but actually the aux fuel pump dying.  On the ground, I turned it back on, and the screeching began again in my ear.  During the approach, I very much stepped up my scan to ensure that the engine was getting fuel flow during that landing without the aux fuel pump on.  However, in a pinch, I know it worked, becasue the pressure did indeed drop as I turned it off.  I knew if it was crash or burning smell for a minute on the approach, I'd turn the pump back on - fortunatly, the plane performed flawlessly on that approach without the aux fuel pump.

I had it replaced (with a new pump instead of overhauled as the cost difference was not huge and there was a new pump sitting at the Mooeny factory - I figure we should all replace parts instead of overhaul as long as they are available if the cost difference is negligible because who knows about the future of the factory - though I think they'll pull through - either on the support end or maybe starting up prodcution again - that's another topic).

If the sound went away, you could chalk it up to moisture causing some sort of short.  It may be something else entirely if it played over a speaker - some sort of interfierence from a device through your intercom.

The reason I share this is becasue the onset occured during a downpour and the syptoms were schreeching through the speaker, and in my case the intercom system.  However, mine ocured in flight and was accompanied by an electrical burning smell. 

Take care,

-Seth

[Shadrach]

I'm not sure what circuit your 396 is wired into.  If it happens again, try unpluging the 396 and see if that stops it.  Not sure if it in fact the stall horn has anything to do with the noise beyond the fact that taking that circuit off line stops the noise. Did you try pulling other breakers? I'm assuming your radio master was off.

[Parker_Woodruff]

Avionics master was off, but subsequently turning the avionics on did not correct the problem.

The Garmin 396 turns on/off with the avionics switch, I believe.  I'll check this afternoon.

[N9937c]

I had the same thing happen on an m20r on a leg from midland to st louis. Nothing got rid of it except master.

Was intermittent for 1 month when I found the stall warning vane was "crooked". My guess was someone washing the plane hit it from the side or walked by and hit it. make sure its square with the slot. doesn't take much to tweek. check stall speed on next flight.

larry

[Skywarrior]

Parker, I just had the same thing happen to me today. I had to pop both the Gear Warning CB and the Stall Warning CB to stop the shrill alarm. This was all on just Master Switch.

I got out and jiggled the stall warning tab to ensure it wasn't stuck. Didn't make any difference.

The plane had not been flown in a month, and was stored in a hangar.

The water-causing-a-short idea sounds attractive, but I really don't know what causes it.

Chuck M.

[N601RX]

If the throttle position switch gets out of adjustment it can make the gear warning go off while inflight.  Usually a little push on the throttle knob to one side or the other will make it stop.

[mooney2201]

there is a relay on the speaker in the overhead vents,,,this relay should open when you transmit,if the relay gets stuck by age or moisture,by a left open vent on the top of the plane,rain may have dripped from vent,,,when you turn on master avionics you will get feedback through the speaker, and i mean bad........replace relay.....

[rxo188]

I have an 87 201 and my stall horn circuit breaker is pulled.  I moved from the FL coast to the CA desert (humid to dry) and the switch started acting up. It degraded over 2 weeks: first it would go off intermittently on the ground when taxiing over asphalt joints, but work well in the air.  Then it would blip in the air when bounced by turbulence.  Gradually it chirped more and more on the ground as it got sensitive to smaller taxiway irregularities, then reacted to lower levels of turbulence, and decided to remain completely ON.  I'm thinking the switch itself in stuck because of the dry atmosphere.  I've seen this in some of my tools that have electric switches. 

Has anyone seen this before? How can I remove, inspect, clean the switch in the wing? Is it through the small access pannel about 2ft behind the switch? Any suggestions will be appreciated.

[Bill_Pyles]

In the last week or so, I have had the same experience Parker described in the original post i.e. the squealing or whistling noise coming through the speaker with just the master switch on, although no rain was involved.   Indeed, when I pull the stall horn CB the noise goes away so I know it is the stall horn.

I liberally sprayed the stall horn with the electrical contact cleaner stuff through the little openings on the leading edge of the wing.  I also removed the panel on the underside of the wing just aft of the stall horn and sprayed the stuff at the stall horn.  This fixed the problem on the ground, but the stall horn started chirping during climb this morning. 

 I thought the horn would go silent after I leveled off, and it did---for a while.  I pulled the CB for a minute or two and eventually the stall horn would stay off, in level  flight, with the CB in the normal "in" position.  Something is not right, and although the electrical contact cleaner helped, the stall horn is still not 100% happy 100% of the time.

I would guess the stall horn is held in place by the screws on the leading edge of the wing, but I expect the aforementioned panel has to be removed in order to service or replace the stall horn.  Anyone done this?