What if? Theoretical GNX375 failure

Discussion in 'Cleared for the Approach' started by asicer, May 18, 2020.

  1. asicer

    asicer Final Approach

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    Suppose you are en route to your destination when your Garmin GNX375 competely fails. You don't have a second GPS and you don't have a second transponder but you do happen to have a NAV/CDI on board so you decide to shoot an ILS or LOC approach. However, the plate says "DME or RADAR required" and the GNX375 was your sole source of DME information. Since the GNX375 was also your transponder, does that also mean you can't fly the approach? Or can ATC legally be of service based off of primary returns?
     
  2. Rgbeard

    Rgbeard Pattern Altitude

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    I believe you're firmly in Emergency territory, during which ATC should set aside the rules, if possible, and be helpful identifying the fixes and step-downs.
     
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  3. Rgbeard

    Rgbeard Pattern Altitude

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    I presume you're choosing the DME-required ILS, because:

    Low ceilings
    No other viable airport with another approach within fuel range
    No other airport with an approach fitting your available equipment and minimums

    I.E., if there was a VOR-A approach to another airport somewhere else, and I had confidence it'd get me there, I'd ask for a redirect, vs. asking ATC to help me identify the fixes at a DME-required ILS. Thus, yeah, it's an emergency, IMO.
     
  4. asicer

    asicer Final Approach

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    I guess what I'm really wondering is if the transponder failure causes a degradation significant enough that affects a radar approach.
     
  5. MuseChaser

    MuseChaser Pattern Altitude

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    I'll have to think about that...

    [​IMG]
     
  6. Rgbeard

    Rgbeard Pattern Altitude

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    I've had a transponder failure, IFR, before. And it wasn't a problem.

    You still come back as a primary target, you're positively identified, and it's effortless (from my perspective) from there.

    In my case, I was climbing through the soup, leaving Catalina Island, and was told my transponder was offline.
    It was a big OMG/WTF moment for me, for a moment.
    I was simply asked to do some turns to identify myself, then got the magic words "Radar Contact", and life continued.
    I was handed off from controller-to-controller, had to do an approach to my destination airport, never had a problem after the magic words.

    I'd think since you were already identified and flying, with radar contact, the transition to being transponderless would be less of an event than if this happened at the beginning of the flight.

    @Radar Contact @Timbeck2 for commentary?
     
  7. Timbeck2

    Timbeck2 Final Approach

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    If I understand the question, yes, if your transponder fails, radar can still "tag you up" and track you using your primary radar return. I haven't worked radar in years but if available, one could ask for a surveillance approach with recommended altitudes. This is a radar question and I'm a predominately a tower guy so maybe one of those will chime in.
     
  8. luvflyin

    luvflyin Final Approach PoA Supporter

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    If you are in Radar Contact you can do it. The only restrictions ATC has on ‘calling the fix’ is sometimes they can’t use ‘Secondary Radar’(transponder) to do it.
     
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  9. MauleSkinner

    MauleSkinner Final Approach

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    I guess I’d rephrase the question to “is a single-point avionics failure going to put me someplace I’m not comfortable with?”
     
  10. Groundpounder

    Groundpounder Pattern Altitude

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    You're still in two way coms? Pick a different approach.
     
  11. asicer

    asicer Final Approach

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    I think this answers my question. It comes down to whether secondary radar is necessary (transponder functional vs failed) to call the fix and it would appear that it isn't.
     
  12. TommyG

    TommyG Pattern Altitude

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    Emergency Situation if you are IMC. Shoot the approach regardless of DME or Radar. Answer the questions later.
     
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  13. Gmonnig

    Gmonnig Pre-takeoff checklist

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    Not an emergency situation if you are in radar contact (which you probably will be). Instead of being a /G you just tell ATC that you lost your GPS and they will know that you lost your transponder because they will have a "primary only" target on you. Losing GNSS and Transpoder No Mode C turns your flight plan into a /X. As long as they have you in RADAR, they can call your fixes.
     
  14. Radar Contact

    Radar Contact Pattern Altitude

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    Very easy to tag up a primary target, separate them, handoff to other controllers etc. Even if you weren’t already ID’ed (which does make it easier) it would just be a commanded turn or two and I can Radar ID you that way. The only difference in the IFR system would be having to report leaving and/or arriving at altitudes so we can go back to using them around you.
     
  15. chemgeek

    chemgeek Pattern Altitude

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    Say the E-word and all is well, using all your backup nav devices, including portable GPS if necessary for positional awareness. And it may be possible for ATC to call fixes for you.

    If you are IFR, you have to report the nav failure to ATC anyway, right? That would normally generate additional questions and intention requests, no?
     
  16. asicer

    asicer Final Approach

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    Why? The scenario is that you have a ILS/LOC and DME or RADAR is required. You lost the GPS so you lost the DME. But if ATC can call the fix then you have RADAR. The original question pertained as to whether ATC can call the fix if the transponder had failed. That was answered in post #8.

    Yes you have to report the GPS/transponder failure to ATC, but does that still constitute an emergency since you still have everything you need to fly the approach?