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Thread: Basic VFR Instruments

  1. #11
    Sam Buchanan's Avatar
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    Quote Originally Posted by Jeff Point View Post
    Thats easy. It’s right after the part that mandates AD compliance for E-AB.
    Aww right, Jeff.........are you saying this is a discussion that will end up in the "Never Ending Debates" section? Good one!

    How does that full panel work on your Breezy????
    Last edited by Sam Buchanan; 09-06-2019 at 07:22 PM.
    Sam Buchanan
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  2. #12
    Jeff Point's Avatar
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    I’m here all week, try the veal and tip the waitresses.
    Jeff Point
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  3. #13

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    Quote Originally Posted by Auburntsts View Post
    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 ďlegalĒ by reg with my EFISís magnetometer. I wanted my AWC so I temporarily installed it a compass to pass inspection. Even though youíre in the right, some battles simply arenít worth fighting.
    This is the best real world answer ever given on the subject.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  4. #14
    EAA Staff Joda's Avatar
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    Quote Originally Posted by Auburntsts View Post
    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.
    Quote Originally Posted by Frank Giger View Post
    This is the best real world answer ever given on the subject.
    Yes, this is the best advice. Every DAR will handle this slightly differently, depending on how their managing office directs them. If I were presented with an aircraft that had no instruments at all in it, I would talk with my FAA advisor and decided how HE wants me to handle it. I would not make that decision in a vacuum. I would want something in writing from my FAA office directing me to go one way or the other. That way the FAA makes the decision, not me. I would keep all the written correspondence regarding the issue with my copy of the paperwork for the aircraft, so that regardless of what decision is made I have a record of the dialog that led up to the decision.
    Cheers!

    Joe

  5. #15
    Sam Buchanan's Avatar
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    I agree a consultation with your DAR is the best route if there is something that might raise a flag during an inspection...and that is advice I've given to builders over the years.

    The only reason I participated in this thread is because there seemed to be a train of thought that stated the regs and orders are clear-cut about an E-AB having complete instrumentation per 91.205 if it is expected to pass inspection. The experimental op lims and order 8130.2 do not support that position and there have been instances of DARs creating hurdles to certification on their own volition with no regulatory basis to deny certification. That is why I wrote in an earlier post "There may be DARs that insist on instrumentation but they are enforcing regulation that doesn't exist".

    I appreciate Joda's input (and was hoping he would respond) and I suspect the unfortunate variability of this matter among FAA managers is intentional...
    Last edited by Sam Buchanan; 09-09-2019 at 05:30 PM.
    Sam Buchanan
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  6. #16
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    I think the FAA is kinda like OSHA, they have regulations but in some cases, they don't want to give you a positive yes or no on any one thing. That's why OSHA has the, "General Duty Clause."
    Bob, just thinking out loud

  7. #17

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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???
    As has been pointed out by several, these items are not required for EAB aircraft. What is required are limitations and how to identify those limitations. For example, if an engine has an RPM limitation, then one must have a tachometer (a way to tell if that limitation has been exceeded). The basis for all regulations is safety, and there are levels of safety in the regulations. Part 25 is more restrictive than part 23 because the original intent of part 25 regulations were written to protect people paying to be transported.

    In addition to 23/25, the regulations are also written to protect the public (those not involved in the activity), passengers (those not in control of operations) and pilots ... and in that order, too. They are also varied for the number of people on board the aircraft ... more people --> more safety/regulations.

    So, back to the original question. (If they were required), GPS altitude and speed would not satisfy the requirement. Airspeed and altitude are both pressures. For airspeed, the limitations on your aircraft are based on pressures/forces: Vs, Va, Vne, Vfe, etc. GPS speed does not measure these pressures. For altitude, the level of safety is now upped a level because this one now involves other people/aircraft. Since GPS altitude (a tapeline/geometric altitude) is different than pressure-based altitude, there could be a mid-air collision. For example, your airplane is cruising east at 7,500' GPS altitude and another airplane (on an IFR flight plan) is cruising west at 8,000' pressure-based altitude. This could be the same, physical altitude.

    Bottom line: No; GPS data cannot be a substitute for pressure-based airspeed and altitude.

    Blue on Top,
    Ron

  8. #18
    Airmutt's Avatar
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    But Ron there are electronic devices ( smart watches, phones, tablets) that can sense pressure altitude. I also have a pic of a Volksplane that has an automotive style altimeter installed. I can set baro on my watch and get pressure altitude too. Do those qualify as an altimeter? Setting the requirement discussion aside, where does it state it has to be a static system driven device. And that is really the crux of my question.
    Dave Shaw
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  9. #19
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    This discussion reminds me of an old story about a college student taking a Physics exam. One question was, "Explain how you can determine the height of a building using a barometer."

    The student wrote down, "Go to the building superintendent, and say, 'I will give you this fine barometer if you tell me how high your building is'."

    The professor marked the answer wrong, and the student challenged it. The prof's boss allowed the challenge, and told the student to answer a modified question: "USING PHYSICS, explain how you can determine the height of a building using a barometer."

    The student answered, "Take the barometer to the top of the building, drop it off, and determine the height of the building using the equation 1/2*acceleration*Time^2."

    In other words, it depends on the INTENT of the requirement.

    Why does an airplane need an airspeed indicator? For a simple indication of the margin above stall. We all know the limitations of this (stall airspeed affected by weight and G-loading), but in GPS-based system can't provide that.

    The second reason is 14CFR 91.117, which limits aircraft to 250 knots or less indicated airspeed below 10,000 feet and includes lower limits for certain airspace. Admittedly, it shouldn't be an issue with our Fly Babies and Piets, but it does indicate how an airspeed indicator may be required for other reasons than 91.205.

    And, of course, we must remember that GPS is never an "airspeed indicator." So if your Operating Limits require an "airspeed," a GPS won't do.

    The second point is the altimeter. In a world where a non-sensitive altimeter is fully legal, a GPS-based altimeter is nominally an acceptable replacement. For those unfamiliar with the term, a non-sensitive altimeter has only one arm and is calibrated in 1000-foot steps, with tick-marks at 200 feet. They often are not adjustable for barometric pressure.

    A GPS altimeter *would* provide the same level of service. The problem is, there are places where non-sensitive altimeter isn't a good pick, and that would follow with the GPS-based unit.

    My home airport lies under the Seattle Class-B airspace, and if I wish to fly out to the west, I have to pass under an arm where the floor is only 1800 feet MSL. It's a congested area, so there's a 1000-foot minimum altitude. What's worse, the ground elevation starts out as 400 feet, so I've got only a 400-foot altitude window...that's just two ticks on a non-sensitive altimeter. They raised that arm several years back...it used to be 1600 feet, so it would have a one-tick range.

    It's the kind of area where you need a reasonable altimeter. Sure, a GPS will provide the needed resolution. But I've got a Mode C transponder and altitude encoder. It's possible that a GPS altitude readout will show me below 1800 feet, but the static-based altitude encoder would show me above. And the ADS-B out would be blabbing my identity. Obviously, I want a my primary cockpit altitude display being static-based altitude.

    *If* the GPS senses static, that might be sufficient. But it has to be "plumbable" into an external, reliable static source. I once experimented with a portable altimeter. It sensed the pressure in the gauge itself, but since the cockpit pressure varies by engine power and aircraft airspeed, it really wasn't accurate.

    Ron Wanttaja

  10. #20
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    Years ago I flew a friend’s Corben. It had a very nice and expensive sensitive altimeter installed. Unfortunately his static system was a piece of tubing stuck up under the instrument panel. It fluctuated wildly. My trusty baro-altimeter watch has a slower response period and was not effected by the turbulence in the cockpit.
    There is an app available where you can plug in local wind speed and direction and it provides TAS. And to make Ron B happy one can even define the airspeed ranges on the display. Is it perfect, no.... but its a free and getting better!!
    Dave Shaw
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