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Thread: Homebuilt Aircraft Fleet Sizes

  1. #11
    rwanttaja's Avatar
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    Quote Originally Posted by DonN View Post
    I counted 312 Tailwinds in the registry, didn't look to see how many new, etc.
    I get about 200. My filter designates it as a Wittman Tailwind if the aircraft model is a "Tailwind" or a "Tail Wind" or variations of W-8, W-9, or W-10 (with dash, or with a space, or no dash or space). There are still a number of false hits, so I don't include Tailwinds in my "standard" set.

    [Edit: This erroneously said "get about 2000". The number was actually 200.]

    Searching Tailwinds is difficult, since some of the designations (e.g., "W10") are used for other aircraft types as well (Augusta AW109SP or VIRUS SW 100, for instance) and you end up with false hits. The false hits are reduced if you don't use wild cards (e.g., "W-8" vs. "W-8*") but then you lose the examples where the builder reverses the order (N214SS, for instance, a "W-8 TAILWIND").

    If there are more reliable search terms, I'd be glad to use them.

    Ron Wanttaja
    Last edited by rwanttaja; 01-03-2021 at 10:54 AM.

  2. #12

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    "66.2% of Experimental Amateur-Built aircraft were active."

    So the active number is about two thirds of the registration total from post one.

  3. #13
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    Quote Originally Posted by rwanttaja View Post
    I get about 2000 My filter designates it as a Wittman Tailwind....
    Please note I had a typo in the above. The actual number of Wittman Tailwind hits I got was 200, not 2,000. Somehow I'd replaced the period with a zero.

    Ron Wanttaja

  4. #14
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    Quote Originally Posted by Bill Berson View Post
    "66.2% of Experimental Amateur-Built aircraft were active."

    So the active number is about two thirds of the registration total from post one.
    I'd prefer to state that as, "The FAA estimates that the active number would be two thirds of the registration total from post one."

    From 2010 to 2013, almost 8,000 homebuilts...about 24% of the entire homebuilt fleet in 2010... were removed from the registry. The FAA Survey active-fleet estimate for homebuilts actually DROPPED in this period (from 59.6% to 58.4%). One would assume that most of those 8,000 removed homebuilts were inactive, even no-longer-existing aircraft. But the upshot is, using the FAA Survey Data, over 3,000 active homebuilts had supposedly quit flying.

    This is why the "official" homebuilt accident rate jumped so much in this time period. Not because accidents increased, but because of the official estimate of active aircraft dropped so much. This triggered a big FAA vs. EAA safety showdown, and a more-reasonable process for monitoring the homebuilt accident rate resulted (based on number of fatalities, not percentage of the estimated fleet).

    The FAA Survey active fleet estimate for homebuilts jumped to 66.1% in 2014, which meant that the number of active homebuilts had decreased "merely" by 1,000 aircraft, from 2010 to 2014. I do not know how the FAA changed their processes to produce this jump. Note that in this same time period, 5,000 new homebuilts had been added to the registry.

    I don't want to belittle the FAA Survey people...they're doing good work, and using good methodology. But the data they use for input has been messed about entirely, and it's not their fault.

    For the 1.3 of you that might be interested on how this came about, I've attached a PDF file explaining what happened.

    Ron Wanttaja
    Attached Images Attached Images

  5. #15

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    Sorry, I can't make any sense from that PDF graphic.
    I think using total fatals instead of percentage is dishonest.

  6. #16
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    Quote Originally Posted by Bill Berson View Post
    Sorry, I can't make any sense from that PDF graphic.
    It works better in a Chapter meeting format where I can provide more background.

    The upshot is:

    Party "A" determines the number of active homebuilt aircraft based on responses from aircraft owners (surveys)
    Party "B" determines the number of active homebuilt aircraft based on the LACK of response from aircraft owners (to the triannual re-registration notification)

    But when Party B eliminates inactive aircraft, it has utterly no effect on the results from Party A. Yet the results from both Party A and Party B are combined as input to accident rate analyses.

    Quote Originally Posted by Bill Berson View Post
    I think using total fatals instead of percentage is dishonest.
    Without a reliable estimate of active aircraft and average annual hours, basing one's assessment based on number of accidents eliminates most of the estimation process. I personally look at all accidents, not just fatals, but if you're looking for a metric, the number of fatal accidents every year is a pretty good one.

    Here's my results for 1998-2019.
    Name:  accident totals.JPG
Views: 179
Size:  25.7 KB
    Ron Wanttaja

  7. #17

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    I didn't use a search, just scanned through the list and counted what I thought were Tailwinds. I know this is not something that you can do for your report. There are SO many ways that people describe their airplanes, and many typo's. Even the variations in spelling wittman, witman, whitman, etc.

  8. #18

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    "but if you're looking for a metric, the number of fatal accidents every year is a pretty good one."

    Only if if the active number doesn't change over time. If the active number declines by half and fatals stays the same then the accident rate doubled by percentage. I can see why that was distressing for EAA when the list was suddenly culled.
    But if the active EA-B flight hour numbers should double in ten years and they still measure by total fatals then the fatal rate has improved 100% by percentage but wouldn't know it.
    The only way to compare with other aircraft types is with percentage, I think.

  9. #19
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    Quote Originally Posted by Bill Berson View Post
    but if you're looking for a metric, the number of fatal accidents every year is a pretty good one
    "but if you're looking for a metric, the number of fatal accidents every year is a pretty good one."

    Only if if the active number doesn't change over time. If the active number declines by half and fatals stays the same then the accident rate doubled by percentage. I can see why that was distressing for EAA when the list was suddenly culled.
    But if the active EA-B flight hour numbers should double in ten years and they still measure by total fatals then the fatal rate has improved 100% by percentage but wouldn't know it.

    The only way to compare with other aircraft types is with percentage, I think.
    Don't disagree with you; after all, that's how I run my comparisons. All it really needs is a consistent process. You don't need to know the percentage of active aircraft; you just compute the percentages and compare the values year-to-year. The FAA re-registration process is trimming out many of the inactive aircraft. In fact, the homebuilt fleet size hasn't changed much since the completion of the first re-registration cycle.
    Name:  homebuilts per year.JPG
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    The problem is, folks want to see a "accidents per 100,000 flight hours" comparison. Do do THAT, they need the FAA Survey estimate of number of hours flown. And that's where homebuilts take it in the keister; the 2019 survey said that fixed wing GA fleet flew an average of 102.1 hours per year, while the average EAB aircraft flew 46.6 hours. Yet 93% of those homebuilt hours are for "Pleasure," while only 35% of the overall GA hours fall into the same category. It's not a fair comparison.

    My own metric for comparisons is weird. I take the average number of accidents per year over a long time span, and divide it by the number of aircraft on the registry in the last year of the time span. It's stinks when someone wants a black-and-white number as to a given airplane's accident rate, but it's great for comparing multiple aircraft...because the process is usually identical for each aircraft type.
    Name:  accident rates.JPG
Views: 172
Size:  44.9 KB
    Ron Wanttaja

  10. #20

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    What about comparing aircraft by total airframe hours logged at time of crash?
    Does the NTSB list aircraft hours on the reports?

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