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Thread: Basic VFR Instruments

  1. #1
    Airmutt's Avatar
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    Basic VFR Instruments

    FAR 91.205 specifies that an altimeter and airspeed indicator is required for flight. What it does not specify if they have to be P-S driven. So the question is if one were to install say a Dynon D3 would this satisfy the requirement. Yes, I understand that airspeed and altitude displayed are GPS derived. Thoughts, comments???
    Dave Shaw
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  2. #2
    melann's Avatar
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    Quote Originally Posted by Airmutt View Post
    FAR 91.205 specifies that an altimeter and airspeed indicator is required for flight. What it does not specify if they have to be P-S driven. So the question is if one were to install say a Dynon D3 would this satisfy the requirement. Yes, I understand that airspeed and altitude displayed are GPS derived. Thoughts, comments???
    My first comment is that §91.205 applies only to "Standard" certificated aircraft unless specified in the operating limitations, such as in Night and/or IFR operations.

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    Dana's Avatar
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    Quote Originally Posted by Airmutt View Post
    Yes, I understand that airspeed and altitude displayed are GPS derived. Thoughts, comments???
    If it's GPS derived, it's not airspeed at all, it's groundspeed. As melann pointed out 91.205 doesn't apply to experimentals so it's not actually required, but you really do want a real airspeed indicator.

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    Airmutt's Avatar
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    Good point about ground speed. While y’all are correct about the specific language of 91.205, FAA Order 8130.2 does drive you back to 91.205.
    Dave Shaw
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    Auburntsts's Avatar
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    Regs aside, this is something you might run past your DAR/inspector. For example, my FSDO inspector insisted on a whiskey compass even though I was “legal” by reg with my EFIS’s magnetometer. I wanted my AWC so I temporarily installed it a compass to pass inspection. Even though you’re in the right, some battles simply aren’t worth fighting.
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  6. #6
    Sam Buchanan's Avatar
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    Quote Originally Posted by Airmutt View Post
    Good point about ground speed. While y’all are correct about the specific language of 91.205, FAA Order 8130.2 does drive you back to 91.205.
    The Operating Limitations for our experimental aircraft do not require compliance with 91.205 or any instrumentation for day VFR operations.

    Paragraph 8:

    8. After completion of phase I flight testing, unless appropriately equipped for night and/or instrument flight in accordance with FAR 91.205, this aircraft is to be operated under VFR, day only.

    This has been debated countless times over the years but it is established practice that instrumentation is required per the Op Lims only for night or IFR flight. There may be DARs that insist on instrumentation but they are enforcing regulation that doesn't exist.

    Using only GPS-derived instruments for day VFR in an E-AB aircraft is permitted per the Op Lims.
    Last edited by Sam Buchanan; 09-06-2019 at 08:35 AM.
    Sam Buchanan
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    FlyingRon's Avatar
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    Sam, those are only the specimen limitations. The limitations are what the inspector puts on your actual aircraft.
    As pointed out, the guidance for the inspection pretty much mandates 91.205-compliance for initial certification. Yes, you're probably free to rip them out and fly day VFR if you want, but that's not what was being asked.
    No, it's not something that "doesn't exist" the guidance is in the same document you are extracting those sample oplims from.

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    Dana's Avatar
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    My understanding is that nowadays the DAR has to build the open lims from the FAA order, no?

  9. #9
    Sam Buchanan's Avatar
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    Quote Originally Posted by FlyingRon View Post
    Sam, those are only the specimen limitations. The limitations are what the inspector puts on your actual aircraft.
    As pointed out, the guidance for the inspection pretty much mandates 91.205-compliance for initial certification. Yes, you're probably free to rip them out and fly day VFR if you want, but that's not what was being asked.
    No, it's not something that "doesn't exist" the guidance is in the same document you are extracting those sample oplims from.
    I just now read FAA Order 8130.2J chapters 2 and 4 and Appendex D (Table D-1) describing the inspection protocol and what is expected when inspecting an aircraft with an experimental airworthiness certificate. The only implication I found that instruments must be installed in the aircraft is the requirement for various V-speeds be recorded during Phase 1. This implies there will be an airspeed indicator.....of some sort (could be a Hall wind meter for a very slow, light aircraft).

    For my education......please point out the section(s) of the Order that require an aircraft with an experimental airworthiness be equipped with instruments (in addition to an implied airspeed indicator) for Day VFR operation when the airworthiness certificate is issued.

    Thank you.
    Last edited by Sam Buchanan; 09-06-2019 at 07:04 PM.
    Sam Buchanan
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  10. #10
    Jeff Point's Avatar
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    Quote Originally Posted by Sam Buchanan View Post
    For my education......please point out the section(s) of the Order that require an aircraft with an experimental airworthiness be equipped with instruments (in addition to an implied airspeed indicator) for Day VFR operation when the airworthiness certificate is issued.
    Thats easy. It’s right after the part that mandates AD compliance for E-AB.
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