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Thread: Transition failure in safety....

  1. #1

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    Transition failure in safety....

    We were kicking around homebuilt safety awhile ago, with the "certified is the only safe way" and "that's not necessarily so" sides well represented.

    We all know that while experimental aircraft have a disproportunate percentage of wrecks versus their portion of the GA planes out there, but what strikes me is this fact:

    "More than half (53 percent) of the E-AB accidents investigated in 2011 involved E-AB aircraft that were bought used, as opposed to having been built by the current owner. "

    http://www.eaa.org/news/2012/2012-01-24_survey.asp

    I was wondering what is really driving that, and came up with some possibilities:*

    1) The buyer of an experimental is moving to a lighter aircraft from a heavier one and hasn't done proper transition training (similar to the problems many PPL's are having when they decide to fly under Sport Pilot rules, where the aircraft require more dilligent handling, particularly in crosswinds).

    2) The builder is physically different from the new owner. For example, my little Nieuport will meet CG requirements using the standard 170 pound dummy weight. However, the seat, pedals, ground trimming, controls, and sweet spot for CG will really be based around my 145 pound, 5'7" body. If some guy at 240 pounds and 6'2" buys it he may be in big trouble when he gets into a little trouble.

    3) The new owner may be clueless on maintenance of an experimental, particularly if the engine is non-certified.

    Any other ideas?

    * This assumes no gross defect in design and building with a proven record of safe operation.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  2. #2

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    My guess (which is what it is) is low time pilots in unfamiliar aircraft, the experimental part is probably just because they're more economical for first timers, I would hazard another guess that experimentals usually don't have a nice POH to instruct pilots to any unusual charateristics that a certified plane doesn't /wouldn't have. Lack of maintenance is probably right up there too.

  3. #3

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    Aside from aircraft related problems (engine, structural, or control failure, all of which are less likely for aircraft which have finished the testing phase, since we're talking about used aircraft here), it would be instructive to compare the accident rates for similar aircraft types. You would expect a higher accident rate in , say, a Pitts compared to a Cessna, but I suspect the rate for a factory built Pitts or Christen Eagle is very similar to the rate for a homebuilt Pitts. Ditto for a Cub and a homebuilt Cub clone. OTOH, Lancairs, for example, have been involved in quite a few accidents... but the accident rate for Cirrus is also much higher than a basic Cessna.

  4. #4

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    Without data showing what percentages of EAB aircraft are builder owned vs buyer owned (or how many hours are builder flown vs buyer flown), the 53% number has zero meaning.

  5. #5
    Quote Originally Posted by Kyle Boatright View Post
    Without data showing what percentages of EAB aircraft are builder owned vs buyer owned (or how many hours are builder flown vs buyer flown), the 53% number has zero meaning.
    Well... I think we can make some reasonable inferences.

    I can't think of a good reason the hours-per-year would be significantly different between the two categories. Both categories will see an increased number of hours during the early portion...flight testing for the builder-own, and "new toy" for the purchased. As about 5% of the homebuilt fleet changes hands each year, I think that (over the long term), a 50% non-builder ownership is probably a good assumption.

    In any case, comparing the *causes* of the accidents should be a fair way to compare. Looking at a 13-year database of homebuilt accidents, 36.4% of builder-flown homebuilt accident were caused by pilot stick-and-rudder errors (what I call "Pilot Miscontrol"), vs. 41.2% of the purchaser-flown. That's a 12% higher rate.

    Median time-in-type is also a bit eye-opening... The builders had a median 78 hours in the aircraft at the time of the accident, while purchasers had about half that time...40 hours.

    What really caught my attention was the difference in some of the pilot judgement categories. Take "Maneuvering at Low Altitude," which covers a multitude of sins committed while unnecessarily flying low. The rate for the purchased homebuilts was nearly 60% higher! This may indicate a bit more caution and care by those who spend years of their life building a plane. IT may also indicate that the flight-test program gets the builders more familiar with hour their planes handle.

    The purchased homebuilts also seem more instances of fuel exhaustion and starvation...indicating that the builders might be a little less willing to trust the fuel gauges, and more familiar with fuel management of the systems they built.

    The rate of "Continued VFR into IFR Conditions" accidents is about the same on both sides...perfectly reasonable, when you think about it, as the airplane generally has little contribution, here.

    Where do the builder-flown airplanes score worse? Mechanical failure, of course, since the builders have to contend with the teething troubles.

    To wrap this up, one of the more arresting statistics was the breakdown of the number of accidents vs. pilot time-in-type. About 19% of builder-flown homebuilt accidents occur within the pilot's first ten hours, vs about 27% of purchased homebuilts. When you consider that the builder-flown airplanes usually have to contend with a higher rate of mechanical issues during that first ten hours, that's a pretty significant jump.

    A couple of years back, I participated with EAA and the FAA into looking at ways to reduce the accident rate for purchased homebuilts. The result was a Advisory Circular AC90-190, "Airman Transition to Experimental or Unfamiliar Airplanes." You can download it at:

    http://www.wanttaja.com/ac90-109.pdf

    You might find that Appendix 4 (Low Inertia and/or High Drag) was written in a familiar style. :-)

    Ron Wanttaja

  6. #6

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    Quote Originally Posted by rwanttaja View Post
    Well... I think we can make some reasonable inferences.

    I can't think of a good reason the hours-per-year would be significantly different between the two categories. Both categories will see an increased number of hours during the early portion...flight testing for the builder-own, and "new toy" for the purchased. As about 5% of the homebuilt fleet changes hands each year, I think that (over the long term), a 50% non-builder ownership is probably a good assumption.

    <snip>

    Ron Wanttaja
    If the 50% assumption is accurate, then the 53% number (or really, the 3% difference) is statistically insignificant...

  7. #7
    I agree with Kyle and will take it one step further. Many builders don't fly a lot, they enjoy building and after a while will sell their plane and build another. Conversely, someone buys an existing homebuilt solely to fly it. I live on an airpark with a lot of activity. We always have build projects going on but it seems that more folks own homebuilts built by someone else than those that built them (and they fly them a lot). So it's quite possible that non builder owned homebuilts account for MORE than 53% of hours flown making them safer.

  8. #8
    Quote Originally Posted by Kyle Boatright View Post
    If the 50% assumption is accurate, then the 53% number (or really, the 3% difference) is statistically insignificant...
    Agreed, if we're talking accident rate (eg, number of accidents per hours flown). My data says purchased homebuilts have a lower rate of mechanical failure, but they make up for it with a higher rate of pilot error, especially errors in judgement. This tends to catch the attention of the FAA.

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