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If I were to redo my avionics to only include a WAAS GPS unit and two comm radios, would anything prevent me from operating IFR? 14 CFR 91.205(d) only states that my airplane must have:

(2) Two-way radio communication and navigation equipment suitable for the route to be flown.

I'm aware that this is not the most bulletproof way to fly hard IFR. In this case, assume that the aircraft is primarily used for currency/proficiency and the occasional light IFR flight.

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  • $\begingroup$ Keep in mind that GPS is not available everywhere or at any time, due to, in bulk: air-segment failure, poor DoP, DoD shutting down or jamming GPS signal in war area, obstruction, solar pulse...). Also WAAS is only available in North America. Galileo/EGNOS still to be made operational for Europe, as well as GAGAN for India. $\endgroup$
    – mins
    Nov 16, 2014 at 9:59

1 Answer 1

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The AIM contains the information required to operate under IFR using GPS1.

To summarize the requirements, WAAS (but not "traditional" GPS) may be used stand-alone without an alternate means of navigation provided:

  • Installation requirements:
    • The WAAS navigation equipment is approved in accordance with TSOC145 or TSOC146
    • The installation is done in accordance with AC 20-138
  • Operational Requirements:
    • The WAAS AFM procedures are followed
    • It is not be used by a commercial operator
  • Preflight Requirements:
    • The GPS database is current
    • The GPS database provider does not have any notices prohibiting the use of any fix or procedure that you are going to use
    • GPS NOTAMs/Aeronautical Information is reviewed prior to each flight
    • A RAIM prediction for the time and route is done that shows no loss of RAIM
    • The flight plan navigation equipment is listed as RNAV

Note that commercial operators are required to have redundant systems or ground based backups in order to use it, and while not required for you, it's a pretty good idea.

1 More specifically, see:

AIM Chapter 1, Section 1 - Navigation Aids

  • 1-1-18. Global Positioning System (GPS)
    • d. General Requirements
    • e. Use of GPS for IFR Oceanic, Domestic En Route, Terminal Area, and Approach Operations
    • f. General Database Requirements
  • 1-1-19. Wide Area Augmentation System (WAAS)
    • c. General Requirements
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  • $\begingroup$ You're not allowed to substitute GPS for a ground-based navaid for lateral guidance on the final approach course, i.e. you cannot legally fly ILS, localizer, VOR or NDB approaches with GPS alone. Also, you may not plan to fly GPS approaches at both your intended and alternate destinations. That means with GPS only you can only fly RNAV approaches and you can't plan IFR flights that require an alternate. That might still be OK, but it's quite limiting. $\endgroup$
    – Pondlife
    Sep 12, 2014 at 14:32
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    $\begingroup$ @Pondlife -- you can plan RNAV (GPS) approaches at both your destination and alternate provided you have TSO-C145/146 nav gear -- but you need the C052 OpSpec/MSpec/LOA, and can only plan down to LNAV minima at the alternate unless you are using baro-VNAV functionality certified under TSO-C145/146, which allows you to use the LNAV/VNAV minima line for alternate planning (which isn't really a big gain in many cases) $\endgroup$
    – UnrecognizedFallingObject
    Oct 9, 2015 at 3:47
  • $\begingroup$ @Pondlife Your first link actually contains the statement that you can use GPS at the alternate (as UnrecognizedFallingObject mentions) if you have the right equipment. $\endgroup$
    – Lnafziger
    Oct 9, 2015 at 5:10
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    $\begingroup$ @UnrecognizedFallingObject I read it again and you're correct, I guess I read that too quickly the first time! However, the point that GPS isn't permitted as a substitute for ground-based navaids once past the FAF is still valid, as far as I know. $\endgroup$
    – Pondlife
    Oct 9, 2015 at 14:12
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    $\begingroup$ @RyanMortensen The AC linked by Pondlife above. However, upon re-reading I would amend my comment to say "VOR" approach, not "VOR or ILS" approach. The AC specifically says RNAV cannot be used in lieu of lateral localizer guidance. $\endgroup$
    – hemp
    Aug 10, 2019 at 6:03

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