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GTX335 config Help- No Altitude Display

Toobuilder

Well Known Member
Just installed a 335 using the little Garmin altitude encoder and the internal GPS. Though I can navigate to the altitude correction page and the field elevation is approximately right, when I go back to the main function page the altitude (flight level) display shows dashes. Based on the config page, it appears the encoder is talking to the transponder, but I must be missing something on some other configuration setting.

Ive run into this on my 327 and 330 transponders before, but always manged to fumble through the settings and get it to show up. Any thoughts from the brain trust?

Not sure that it makes any difference, but it is also wired to the non waas GNS430 in an attempt to retain the TIS info it had before.

Appreciate the help.
 
Just installed a 335 using the little Garmin altitude encoder and the internal GPS. Though I can navigate to the altitude correction page and the field elevation is approximately right, when I go back to the main function page the altitude (flight level) display shows dashes. Based on the config page, it appears the encoder is talking to the transponder, but I must be missing something on some other configuration setting.

Ive run into this on my 327 and 330 transponders before, but always manged to fumble through the settings and get it to show up. Any thoughts from the brain trust?

Not sure that it makes any difference, but it is also wired to the non waas GNS430 in an attempt to retain the TIS info it had before.

Appreciate the help.

Michael,

In the sensor configuration did you enable the internal altitude encoder (GAE), enter the operational ceiling, enter the number of calibration points (minimum of 3), and calibrate the GAE to the specified number of calibration points?

The internal altitude encoder does not work until you complete the calibration.

Steve
 
Michael,

In the sensor configuration did you enable the internal altitude encoder (GAE), enter the operational ceiling, enter the number of calibration points (minimum of 3), and calibrate the GAE to the specified number of calibration points?

The internal altitude encoder does not work until you complete the calibration.

Steve

Yes, yes, yes, and not sure. I guess I'm unclear on the "calibrate" function. Will have to open up the sensor page and look for that command. Is it "start", "go", or something intuitive?
 
The internal altitude encoder has to be calibrated or it will not work. Most likely only a garmin dealer can do the calibration.
 
Yes, yes, yes, and not sure. I guess I'm unclear on the "calibrate" function. Will have to open up the sensor page and look for that command. Is it "start", "go", or something intuitive?

Michael,

As we discussed above, you start out on the Internal Alt Encoder Installed page and specify the following information.

GTX 3X5 Internal Alt Encoder Installed Page.png

Next, the Internal Alt Encoder Adjustment page is used to calibrate the altitude encoder to your existing primary altitude source for the number of calibration points you specified.

GTX 3X5 Altitude Cal.png

It is a pretty straightforward procedure. Just a single page in the GTX 3X5 STC installation manual. You basically adjust the static pressure so your primary altimeter reads one of your 3 or more calibration altitudes (e.g. -1000', 10,000', 20,000'), then use the 8 and 9 buttons to increase/decrease the Correction value until the GAE Alt Encoder Measured value equals the Test Alt.

Once the Correction value is set for one Test Alt, push the ENT key to go back to the Test ALT selection to start the next altitude calibration. Once all test points are successfully completed, push the CRSR key to exit.

Steve
 
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I don’t think this is something an individual can perform under the FAR’s
According to the regs Altitude reporting is required in class A B and C airspace.
91.215
Also when operating under IFR the encoder must be calibrated every two years.

The regs state that this must be performed by a certified avionics repair station, and this applies to experimental aircraft too.

I took my internal encoder to my local avionics shop and they calibrated it on the bench for a very nominal price.
 
I took my internal encoder to my local avionics shop and they calibrated it on the bench for a very nominal price.

Not sure how a Garmin GAE module could be calibrated on the bench without it being installed on the transponder?

If the altitude encoder or altimeter is replaced, then they must be tested/adjusted to verify they match within 125' of each other, this applies to all aircraft.

During an IFR cert this tolerance is verified every 2 years.

Must be done by a certified repair station that is appropriately rated.
 
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Ok, light bulb just went off. This calibration is done while the pitot static system is being exercised by a huffer/puffer test set like a TTU-205. Other transponders I've installed were looking at external encoder sources through a serial data stream and would eventually pop up with the altitude display. This would be refined with a pitot static checkout, but there would at least be an initial display.

So this setup will not even function unless its run through the whole calibration?

At any rate, makes sense now. Thanks for the shove in the right direction everybody!
 
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