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5 Answers

GPS legal substitute for ADF

Asked by: 3092 views , , ,
General Aviation

So I am flying safety pilot for a friend. His plane has dual VORs of which one has GS. His GPS is a Garmin 150XL and is not certified for IFR. During his training his instructor told him his type is /G. Is she right?

A GPS is a legal substitute for ADF but is THIS GPS a legal substitute for an ADF? The only approach into his airport is an NDB. Unfortunately the nearest alternate has an ILS but the plate clearly also requires an ADF as the NDB is an IAF.

He wants me to show him how to fly this approach and I would like to do this for him as I would rather see him use it rather than try to scud run in MVFR.

Comments anyone?

 

 

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5 Answers



  1. John D Collins on May 30, 2018

    No way is the Garmin 150 XL a suitable RNAV system.

    AC 90-108 specifies what is a suitable RNAV system:

    6. TYPES OF RNAV SYSTEMS THAT QUALIFY AS A SUITABLE RNAV SYSTEM.
    When installed in accordance with appropriate airworthiness installation requirements and operated in accordance with this AC, the following systems qualify as suitable RNAV systems:
    a. Systems Using TSO-C129/-C145/-C146 Equipment. An RNAV system with TSO-C129/-C145/-C146 (all revisions), equipment, installed in accordance with AC 20-138 (all revisions), Airworthiness Approval of Positioning and Navigation Systems, or AC 20-130A, Airworthiness Approval of Navigation or Flight Management Systems Integrating Multiple Navigation Sensors, and authorized for IFR en route and terminal operations (including those systems previously qualified for “GPS in lieu of ADF or DME” operations)

    The Garmin 150XL is not authorized for IFR enroute or terminal operations, not is it installed in accordance with any version of AC 20-138.

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  2. John D Collins on May 30, 2018

    Even if his GPS was IFR, which it is not, the approach is not loadable from the database and the final approach course must be flown with a working ADF, working NDB station, and the course must be displayed on an RMI or ADF indicator and must be monitored on final approach for course alignment.

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  3. Stephen Kaloroplos on May 30, 2018

    I appreciate your answer. I have read FAA AC No:90.108 so I have to agree.

    So why do you think his flight instructor told him to file /G. He is not taking my word over hers. One possible reason she would say /G could be his GPS does have RAIM Prediction and Autonomous Integrity Monitoring which is generally a feature that separates IFR and VFR receivers.

    He is a friend and I want to show him this approach for emergencies but not until he totally understands it is illegal because he is not /G.

    Are you a CFII? If you are I will show him this post.

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  4. KDS on May 31, 2018

    John is a subject matter expert in such things. You can accept his words without hesitation.

    To your question of why would the instructor say otherwise; that boils down to people are human and make mistakes even when they are trying as best they can.

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  5. Mark Kolber on Jun 01, 2018

    So why do you think his flight instructor told him to file /G.
    Either one of two reasons I can think of:

    1. Your friend is a VFR-only pilot. VFR pilots filing equipment codes is a common convention not a rule. So, VFR, it really doesn’t matter what equipment code you file. Recall that ATC never sees those. They are potential S&R filings. This gets clarified (sometimes) during instrument training.

    2. The CFI doesn’t know what she’s talking about.

    I vote for No. 1.

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