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Gear Warning


Glen Davis

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Guys,

1984 M20J question:

At what MP does the gear warning system kick in and the beep-beep-beep-beep start sounding?   Is the sound generated directly from the Sonalert or is it tied into the overhead speaker?  I don't hear it in my headset, only from the overhead panel.

Glen

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From the M20J Service Manual:

  The landing gear warning system provides the pilot with an audible warning that the landing gear is not down and locked when the throttle is retarded to within 1/4 to 3/8 in. throttle position.  [...]  This warning switch is mounted on the throttle housing forward of the instrument panel, and can be adjusted for the proper setting by loosening the screw and repositioning the switch.

The system isn't connected to the manifold pressure gauge in any way, and doesn't "know" the MP setting at which it actuates.  With trial and error, you can get it to actuate at a particular MP value on a particular day at a particular altitude, but the actual MP it switches at on other days will vary, depending on altitude and atmospheric conditions.  When deciding where to set it, one consideration is how often you land at high- vs. low-density altitude airports.  The MP you get at a particular throttle position can vary quite a bit at different altitudes.

The beeping noise triggered by the gear warning system is sounded by a Mallory Sonalert installed in the ceiling.  It's a little black round thing, slightly bigger in diameter than a quarter.  It is unrelated to the overhead speaker that broadcasts audio from the radios.  Below is a picture from the M20J service manual identifying the gear and stall warning Sonalerts relative to the overhead lights and other things in the overhead panel.

image.png.46aafee4b869d5a7bdce536f93bb2e33.png

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Vance,

THANK YOU!  That is exactly what I needed to know.  If my mechanic is not familiar with this systems, and specifically the information you just provided, I will share it with him.  Actually, this is a new mechanic for me.  He told me he maintains a couple of J models.  If he know this, good for him.  If he doesn't, I have this to share and don't have to pay for his learning curve.  Love Mooneyspace.  Thanks again, Vance.

Glen

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If it were me, and I was evaluating a new mechanic, I might not give him the details up front, even if he hasn't performed this particular adjustment before.  The learning curve is only a few minutes of leafing through a service manual he should already have and be pretty familiar with, considering he "maintains a couple of J models".  It's a good test of whether he has and uses the factory manuals to maintain the airplane, vs. winging it.

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Glen for your own records...

getting a set of maintenance and parts manuals isn’t too hard or expensive...

Your mechanic knows he needs access to such documentation to work on the plane...

Sure helps when you have Vance’s details in your hand... :)

Best regards,

-a-

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On later M20Js, the stall warning and landing gear warning are generated by an electronic module and sound through the headset and a second cabin speaker rather than a sonalert.

Adjusting the microswitch located on the throttle cable just behind the console is a trial and error thing. You might want to do this yourself. It requires no special skill other than using a small screwdriver while wedged in the left footwell :).

Skip

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From what I recall, loosening these two nuts you can slide assembly forward of aft.
also, it is imperative that throttle cable travel enough rearward to allow for the detent in the cable.  This may require adjusting throttle linkage up to the servo.

Isn’t the nuts I circled the ones you loosen and slide the switch as required?

e2c9d6f0113754461f7481a21f8f5e5b.jpg
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3 hours ago, ArtVandelay said:


Isn’t the nuts I circled the ones you loosen and slide the switch as required?

e2c9d6f0113754461f7481a21f8f5e5b.jpg

Sort of. The switch on the lower left is for the ram air annunciator and the one on the upper right is for the throttle gear warning. They both work the same way. The red circled screws attach the whole switch assembly to the cable and the yellow circled screws adjust the switch position (except you want to adjust the switch on the throttle, not on the ram air cable). 

1167159124_Screenshot2020-11-29at7_53_25AM.thumb.png.64ed8a83c2540b0e23ba486cd1683628.png

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  • 2 years later...

This is an old thread, but I searched Mooneyspace and didn't see any reference to the gear warning switch on the Ovation, so I thought it worthwhile to share in case another late model owner is chasing down a gear warning issue.  

I recently had an inop gear warning on my Ovation and had to track down the gear warning switch.  I looked at the throttle cable right behind the panel and didn't see the switch that is pictured earlier in this thread. 

I reached out to Savvy and @kortopates pointed me toward looking on the engine side of the throttle cable.  And, sure enough, right where the cable attaches to the throttle body is the small switch as seen in the picture below.  

Hope this helps someone down the line.

Cheers,
jamie

 

IMG_5180.jpg

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