Narco AT165 no pressure alt

Discussion in 'Avionics and Upgrades' started by jd21476, Mar 24, 2020.

  1. jd21476

    jd21476 Pre-takeoff checklist

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    I just recently swapped out my AT50 for an AT165. Ive flown it a couple of times and it seemed fine but today ATC said they could not see my Altitude.
    The display did not show anything under Pressure Altitude but it did show ALT.
    The ATC said it may have been his equipment as opposed to mine and I have not had a complaint before.

    Should pressure alt be registering or is the ALT display sufficient.
     

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  2. flyingron

    flyingron Touchdown! Greaser!

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    Sounds like the transponder and the encoder got failure t'communicate. The ALT control position/annunciator just says the transponder will respond (without useful data) to mode C interrogations. You can get it into that mode even if you don't have an encoder connected at all.
     
  3. asicer

    asicer En-Route

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    Pressure altitude is what gets transmitted to ATC, so if you don't see it then they won't see it either.
     
  4. jd21476

    jd21476 Pre-takeoff checklist

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    So if I pulled out my old AT50 and did a one for one swap with the AT165 shouldn't it read altitude also? Does the AT165 need some sort of altitude encoder or something that I may be missing?
     
  5. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    Is it possible the switch that controls whether the pin is 5 is digitizer common or alarm audio output is in the wrong position and has disabled the encoder?

    Screen Shot 2020-03-24 at 2.41.54 PM.png
    Screen Shot 2020-03-24 at 2.42.36 PM.png
     
  6. jd21476

    jd21476 Pre-takeoff checklist

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    Hhhhmmm, I dont know. What kind of alarm audio should I get? Is it somethingbId hear in my headset, and if so, when?
     
  7. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    What I mean is if that if your encoder was wired to that pin on the AT50 ("strobe" which tells the encoder to start transmitting altitude), and you slid in the AT165, and the switch is set wrong, it's not sending the signal it needs to know to start outputting altitude. You wouldn't heard audio unless you did re-wiring.
     
  8. jd21476

    jd21476 Pre-takeoff checklist

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    So its not like there is just some switch on the AT165 that I just push to the left or to the right and suddenly it should work? This would be something I need to take to an avionics shop to check out, right?
     
  9. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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  10. jd21476

    jd21476 Pre-takeoff checklist

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    Ok, so Ill have to check the switch. Any idea where it is located?
     
  11. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    I've never physically seen it, but manual says right side of the unit. It's probably a small switch behind an opening in the case. Hopefully labeled :)
     
  12. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser!

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    When you installed the transponder, it got checked as per 91.413 before you used it and it was OK, right?
     
  13. jd21476

    jd21476 Pre-takeoff checklist

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    I will take a look when I get a chance. Thanks
     
  14. flyingron

    flyingron Touchdown! Greaser!

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    Note that pulling transponders and reinstalling them is *****NOT**** an owner-pilot allowed piece of maintenance. Get thee to a repair shop.