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Thread: Homebuilt Aircraft Fleet Sizes

  1. #21
    rwanttaja's Avatar
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    Quote Originally Posted by Bill Berson View Post
    What about comparing aircraft by total airframe hours logged at time of crash?
    Does the NTSB list aircraft hours on the reports?
    The NTSB lists the airframe hours on about 75% of the homebuilt accidents. My Cessna 172 accident database shows about 82% of the accidents had aircraft hours.

    Otherwise, the average GA aircraft is older and has a *lot* more time. The average time on the 172s was over 5,000 hours, while the homebuilts had an average of about 350. Wouldn't really be a fair comparison.

    Here's a plot of aircraft time vs. number of homebuilt accidents over a 22-year period.
    Name:  accidents vs hours.JPG
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    Ron Wanttaja

  2. #22

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    Quote Originally Posted by rwanttaja View Post
    The NTSB lists the airframe hours on about 75% of the homebuilt accidents. My Cessna 172 accident database shows about 82% of the accidents had aircraft hours.

    Otherwise, the average GA aircraft is older and has a *lot* more time. The average time on the 172s was over 5,000 hours, while the homebuilts had an average of about 350. Wouldn't really be a fair comparison.

    Here's a plot of aircraft time vs. number of homebuilt accidents over a 22-year period.
    Ron Wanttaja
    It would be interesting to see the data normalized against the number of aircraft that have reached a particular "Aircraft Time" level. IOW, if only five planes have reached 900 hours, and 4 of them crashed at 900 hours, that's a lot worse than 1000 planes reaching 100 hours and 75 of them crashing.

    Does the data exist to do this analysis?

  3. #23
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    Quote Originally Posted by Marc Zeitlin View Post
    It would be interesting to see the data normalized against the number of aircraft that have reached a particular "Aircraft Time" level. IOW, if only five planes have reached 900 hours, and 4 of them crashed at 900 hours, that's a lot worse than 1000 planes reaching 100 hours and 75 of them crashing.

    Does the data exist to do this analysis?
    I can pretty much guarantee it doesn't. Just as there is no requirement to report the number of hours per year flown by pilots, there is no requirement to regularly report airframe time flown on Experimentals - or most GA airplanes, for that matter. No requirement, and to the best of my knowledge no process or place to report it even if you wanted to.

    The FAA has a record that my plane exists, and that it has current registration, but no idea of the current hours. I suppose if someone were to crash it AND enough of the Dynon survived to tell the tale they might recover that information, or they could see the hours recorded during the most recent condition inspection. That's about it.

    This is why I am somewhat suspect of any statistics on the number of hours flown per year by the GA or Exp fleet. I don't know how big a sample size is used, or what percentage of owners respond to the survey, but it's a statistical guess.
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  4. #24

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    Quote Originally Posted by rwanttaja View Post
    The average time on the 172s was over 5,000 hours, while the homebuilts had an average of about 350. Wouldn't really be a fair comparison.

    Here's a plot of aircraft time vs. number of homebuilt accidents over a 22-year period.
    Ron Wanttaja
    It isn't fair that homebuilts have more fatals, but is reality. My mother-in-law told me life isn't fair.
    I think the data needs to list the fatal rate for each homebuilt type from zero to 200 hours aircraft time.

  5. #25
    rwanttaja's Avatar
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    Quote Originally Posted by Bill Berson View Post
    It isn't fair that homebuilts have more fatals, but is reality. My mother-in-law told me life isn't fair.
    I think the data needs to list the fatal rate for each homebuilt type from zero to 200 hours aircraft time.
    Interesting suggestion. Here's a cut at it, for aircraft types with 50 or more accidents from 1998 through 2019.

    Fatal Rate: Percentage of ALL accidents of that type that resulted in at least one fatality.

    Fatal Rate for A/C with <200 Hours: Percentage of fatal accidents of that type that HAD an entry for aircraft time, and the aircraft time was less than 200 hours.

    Percentage of Accidents with <200 Hours: Percentage of all accidents that HAD an entry for aircraft time, and the aircraft time was less than 200 hours.

    Last line of the table gives the overall for the homebuilt fleet.
    Kennel Name
    Fatal Rate
    Fatal Rate for A/C with <200 Hours
    Percentage of Accidents with < 200 Hours
    Avid*
    7.9%
    3.8%
    49.4%
    Challenger II*
    34.6%
    12.0%
    64.0%
    Glasair*
    31.3%
    3.0%
    28.4%
    Glastar*
    10.8%
    6.5%
    52.2%
    Kitfox*
    14.1%
    2.4%
    45.6%
    Lancair 4*
    52.2%
    20.4%
    46.9%
    Lancair Two Seat*
    40.5%
    11.7%
    33.8%
    Pitts*
    20.8%
    5.0%
    26.7%
    Rand KR-2*
    24.0%
    5.6%
    55.6%
    ROTORWAY*
    6.5%
    5.2%
    78.1%
    Rutan Long-EZ*
    17.6%
    5.6%
    25.0%
    SeaRey*
    19.7%
    8.7%
    60.9%
    Sonex*
    28.0%
    13.9%
    72.2%
    Starduster*
    13.1%
    0.0%
    19.1%
    Vans RV-4*
    28.4%
    3.0%
    22.4%
    Vans RV-6*
    26.5%
    4.9%
    27.6%
    Vans RV-7*
    33.3%
    6.3%
    45.8%
    Vans RV-8*
    27.4%
    7.9%
    47.6%
    Velocity*
    19.7%
    13.0%
    58.7%
    Zenair CH-601*
    20.5%
    10.6%
    74.2%
    Zenair CH-701*
    11.8%
    1.8%
    70.9%
    Overall
    24.1%
    9.0%
    51.7%

    Interesting how lower-time homebuilts have a lower fatality rate. I thought at first it was might be because of an increased rate of early-life engine issues, but the <200 hour's power-failure rate isn't that much higher than the overall fleet.

    Ron Wanttaja

  6. #26
    Dana's Avatar
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    If you crash, the FAA or NTSB will ask to see the aircraft logbooks... they did when I had my accident.

  7. #27

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    The danger zone is probably the less than 100 hours in type. That's why insurance companies want 100 hours in type.

  8. #28
    rwanttaja's Avatar
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    Quote Originally Posted by Bill Berson View Post
    The danger zone is probably the less than 100 hours in type. That's why insurance companies want 100 hours in type.
    Yep, makes sense.

    Name:  time in type.JPG
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    You'll notice how the NTSB guys like to round up... spikes at 100, 150, 200, etc.

    Ron Wanttaja

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