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Rick Ludtke

Rick Ludtke

New member 59 From Whidbey Island, WA
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  • neald
    Rick,

    Your post is restricted and cannot be replied to. The Dynon HDX is very interesting. The autopilot integration appears solid and restrictions seem minimal. The only puzzle is how to we get the altitude restriction down to 200 ft for the Commander (typical ILS DA)? The 172 is close at 250, but the Bonanza is up at 425.

    Regards,
    Neal
    Rick Ludtke
    Rick Ludtke
    Hi Neal,
    The altitude restriction is driven by regulation, and is a result of the FAA's test pilot measurement of the airplanes altitude loss from the beginning of a servo nose down hardover initiated during a stabilized approach, to the point that the test pilot recognizes the failure, plus one second. This value is adjusted downward to consider the location of the airplanes wheels, and applied to 1:29 slope from the runway threshold (which represents the bottom of the protected airspace of a nominal 3 degree approach glide slope). The point where the altitude loss measurement will not break the plane of the 1:29 slope represents the latest location that a hardover event can occur. So working backwards from the point that the airplane is recoverable without breaking the 1:29 slope, the FAA arrives at the minimum altitude limit. The big player in this scenario is approach speed. The faster the approach speed, the higher the minimum altitude.

    There isn't much that can be done differently, this is the accepted Means of Compliance. It is true that Dynon could propose an alternate means of compliance, but what? On approach, at approach speeds, close to the ground, it is obviously very important to avoid hitting the ground in the event of a servo failure. Safety is paramount. I personally do not disagree with the FAA regulation in this case. AC 23-17C page 260 has a nice diagram describing the Acceptable Method for Determining Altitude Loss In Approach. https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_23-17C.pdf

    While a servo hardover is accepted by the FAA to be extremely improbable, we can't provide any data proving that it will never happen in our system. This is very difficult to do with digital systems and software, without a significant investment of resources. If we did, we would be selling this autopilot to corporate and commercial jet owners for a million bucks a pop.

    Obviously this regulation can't take into consideration every airport, and so it is conservative (for instance the application of the extra second delay). How people choose to actually use their autopilot will vary from pilot to pilot, and airport to airport, and conditions to conditions.

    I hope this helps.

    Rick
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