Squealing noise

[laytonl]

I remember a previous thread about this but can't find it. Last week in extremely heavy rain my stall warning started squealing and wouldn't stop. I pulled the CB to no effect and then pulled the gear CB and it stopped. Pushed the stall CB back in and it started again. It would only stop when both the stall and gear CBs were pulled. As soon as I landed, the squealing stopped and hasn't reoccurred.

Anybody else experience this?

Lee

[tony]

I don't know what model you have, but if it were my airplane it would be a bad micro switch on the throttle cable.  If it happens to you again in flight, gently rock the throttle from left to right to see if that works for you so its not so annoying until you get a chance to repair it.

[Skywarrior]

Yep, I've experienced this in my Bravo. It went away on its own, probably because the microswitch dried out. You may wish to keep a hair blow dryer at your hangar, to dry out the stall sensor area before flights.

 

Some people have had their switch stick in the 'Up' position because they draggged a fuel hose across it, and they reset it by pushinjg down on the vane.

 

If I had pushed on *my* stall vane, I wopuld have broken it!

 

So, I believe that water intrusion is an alternate cause scenario.

[bumper]

Tony, I think you might be confusing the stall warning for the gear warning . . . the throttle detent micro-switch is for the gear warning.

 

On my '87, Mooney uses a solid state piezo sounder (Sonalert) for the stall warning. These have a fairly high impedance, so don't take much power to sound. A dirty wet stall stall switch may pass enough current to do make it sound (squea) even when the switch is "open". I suggest the following:

 

With a felt tip, mark the stall switch mounting plate so you can install back at the same position (the mounting screw holes are slotted for to adjust when the vane closed relative to AOA). Remove stall switch and spray with contact cleaner - - I've had silicone spray work for this too, but can't guarantee it. Move vane back and forth to exercise switch a few times and check for normal operation. Re-install.

 

bumper

[tony]

Yes, you are right, I was.   I need to read more carefully.

[laytonl]

Thanks Bumper, I may give your suggestion a try.  This is a '92 MSE and it only occurs in very heavy rain, so I suspect it is water in the stall switch.  On a subsequent flight in "dry" weather the problem did not occur.  Lee

[jlunseth]

Happened to me last weekend in my 231. Stall alert would not quit. A little unnerving because I had to shoot an ILS to near minimums. A & P says they fixed it, have not heard what the cause was but I am guessing water in the switch.

[320KPH]

It wasn't a scared passenger was it?

[laytonl]

Squealing passenger is always a possibility when I'm flying, but it does seem to be related to the Stall switch. Lee

[KSMooniac]

It could be an accountant making that noise too.  

[laytonl]

Happened to me last weekend in my 231. Stall alert would not quit. A little unnerving because I had to shoot an ILS to near minimums. A & P says they fixed it, have not heard what the cause was but I am guessing water in the switch.

I would love to know how your mechanic fixed it. I was in heavy rain again yesterday and the stall horn squealed again until I pulled the stall warning and gear warning breakers.

Lee

[rgpilot]

My 93 M20J was doing the exact same thing. Same result by pulling both circuit breakers. Found that the vane was slightly out of position and sticking partially in the upward position. Pulled on it a little and that straighten it out enough to solve the problem. I remember my AP hit it doing the last annual, but didn't want to try to change it until I flew it. It was bent down enough to stick. Now I just have to see if it comes on at the correct stall speed.