Sonex Accidents and Accident Data

[markschaible]

Hello SonexBuilders.net

It’s been a troubling and interesting last few weeks in the Sonex world with regard to accidents and accident data. Troubling of course in that we had two accidents in the builder fleet during this period, one fatal and one thankfully with only minor injuries. Investigations will hopefully bear more insight into the causes of both accidents with lessons that can benefit the worldwide fleet at-large.

The interesting part of the last couple weeks came in the form of discussions about accidents in the Sonex fleet both here on SonexBuilders.net as-well as at Sonex Aircraft, LLC in addition to discussions about accidents in the homebuilt fleet at-large. As part of my role serving on the EAA Safety Committee I was able to attend a virtual presentation during the EAA Homebuilt Aircraft Council’s Fall meeting by Ron Wanttaja on Thursday November 11th. The presentation was entitled “What Kills Us: A Look at Fatal Homebuilt Accidents and their Causes” and was extremely interesting and insightful. Ron will be giving this presentation with some updates and further research during the 2022 EAA Homebuilder’s Week schedule of events in January and I would recommend that everyone check it out.

If you’re not familiar with Ron Wanttaja: Ron is a retired Boeing space systems engineer who has been studying homebuilt accidents as a hobby since 2000. He is a frequent contributor to Kitplanes Magazine and all of his articles are worth reading and re-reading periodically (one of his recent articles was linked in the recent SonexBuilders.net discussion of accident data). Ron has gained a tremendous amount of respect for his work because he goes far-more in-depth with his analysis of homebuilt accidents at the statistical level than the FAA, NTSB or even the Nall Report folks do. Ron is a regular presenter at DOT/TSI homebuilt accident investigation courses. Ron flies a Flybaby and entertainingly points out that he “has no dog in this hunt” when comparing popular homebuilt aircraft types.

During Ron’s presentation, he showed the same thing that we’ve been reporting at the EAA Safety Committee for several years: That the overall accident rate and fatal accident rate have been trending consistently downward while the number of homebuilt aircraft and homebuilt aircraft flight hours has been steadily increasing.

Ron also illustrated that loss of control (or “pilot miscontrol” as Ron terms it) accounts for a lot of accidents and a lot of fatalities in the homebuilt fleet at-large, including miscontrol both with and without loss of engine power and during low-level maneuvering (the stupid kind). This reinforces the need for pilots of homebuilt aircraft to practice stalls, both normal and accelerated, and to install & calibrate AOA devices in their aircraft whenever possible (AOA with audible warnings are preferred). One technique that we’ve been discussing in the EAA Safety Committee working group for the EAA Flight Test Manual has been practicing power-off accelerated stalls without application of power to affect recovery from the stall. This can be a valuable exercise to familiarize a pilot with the amount of rapid pitch-down response required to keep the aircraft flying when there is a loss of power during climb-out and in other critical situations.

Ron also went-on to show a comparison of fatality rates between various homebuilt aircraft types in-which Sonex aircraft were shown to have statistics quite similar to most other popular types. Given the discussion on SonexBuilders.net earlier in the week, this and other data points prompted me to follow-up with Ron to get more information from his database.

When discussing the report on SonexBuilders.net of an 11.1% Sonex aircraft accident rate and a 3.4% fatality rate with Ron, I received the following response from him:

I did a search for Cessna 172s on the January 2021 registry: 20,772 Since January 2000, there have been about 2800 Cessna 172 accidents

That's a 13.4% accident rate! Call the FAA! Call Ralph Nader! :-)

So no, I don't consider that a legitimate way of calculating accident rates.

Incredibly, Ron Wanttaja was able to provide me with the attached report of Sonex accident statistics in less-than 24 hours after I had initially contacted him. Take a look. The attached report and more detailed competitive comparisons shared with us by Ron shows that Sonex aircraft have an average annual accident rate in the US fleet in the period between 1998 and 2020 of 0.92 percent with 2020’s accident rate coming-in at 1.14%. Both fatal and non-fatal Sonex accident rates appear to be “in family” with other light homebuilt types according to the attached report.

Sonex aircraft, light other light homebuilt aircraft, tends to appeal to pilots with less flying experience. The median flying experience of Sonex pilots involved in accidents is about half that of the overall accidents: approximately 484 hours on-average vs. an average of 1,000 logged hours for pilots involved in accidents across the entire homebuilt fleet.

While the pilot miscontrol rate for the Sonex fleet is lower than average (approximately 34% vs. 40% for the homebuilt fleet at-large), Sonex pilots are encountering over twice as many stalls after an engine failure vs. the greater homebuilt fleet (36.8% for the Sonex fleet vs. 15.5% for the entire homebuilt fleet). This reinforces the need for stall practice and practice of engine out scenarios among Sonex pilots.

With the Sonex fleet being larger than ever, and with so many aircraft changing hands, we asked Ron to look at statistics involving Non-Buider Owners, or “NBO’s” both in the Sonex fleet, and in the homebuilt fleet at-large. While Sonex NBO’s are not accounting for more accidents overall in the Sonex fleet, it’s important to note that Sonex NBO’s are more likely to have an accident in the first 10 hours of operating their new aircraft than original builders are during the first 10 hours of the aircraft’s phase I flight testing.

Loss of Engine Power:
The Sonex aircraft fleet does suffer from a higher than average rate of accidents due to loss of engine power: 50% vs. 31% for the entire homebuilt aircraft fleet in the U.S.

A look at Ron’s raw database of Sonex accidents from 1998 to 2020 in the United States gives the following breakdown:
• AeroVee Installations: 17 total accidents
• Loss of Power: 12 accidents
• Fatal Accidents: 6

• VW Unknown or Other (aircraft with Great Plains, Revmaster or just registered as “Volkswagen”): 9 total accidents
• Loss of Power: 3
• Fatal Accidents: 2

• Jabiru (includes 2200 and 3300 models): 20 total accidents
• Loss of Power: 6
• Fatal Accidents: 6

Looking at the Sonex Aircraft Completions Gallery on our web site, you can see that the fleet of flying Sonex aircraft (as reported by builders) is comprised of the following with respect to VW’s and Jabiru’s (the two most-popular types of Sonex powerplants although there are aircraft flying with engines such as Rotax, UL Power and others):

• AeroVee Installations: 306 aircraft
• VW - Other Types: 33 aircraft
• Jabiru (2200, 3300 and CAMit engines): 271 aircraft

It’s also quite significant that Ron’s database shows that among fixed-wing homebuilt aircraft involved in accidents that had auto conversion engine types installed, 50.6% involve loss of engine power (the total across all automotive conversions including rotorcraft is 44.4%). For “Non-Certified 4 Stroke Engines,” which would include Jabiru engines, the figure is 25.8%. These numbers across the entire homebuilt fleet are in relatively close alignment with the Sonex numbers shown above for both VW and Jabiru engines.

While VW engine conversions such as the AeroVee have been great and economical homebuilt aircraft powerplants for many decades, there are differences between these engines and “certified” engines along with differences vs. “non-certified aircraft engines” such as Jabiru and Rotax. We’ll be looking more into VW and other auto conversion engines at the EAA Safety Committee with regard to possible education and outreach efforts.

Sonex Aircraft publishes very comprehensive firewall forward installation guidance for both AeroVee and Jabiru engines, along with detailed AeroInjector documentation, and it is all published for free download on the AeroConversions.com web site (Jabiru/Sonex Installation Guide has just been made available as a free download vs. being paired with purchase of our Jabiru Baffle Kit). All the documentation (and free tech support advice) in the world isn’t going to help if builders do not follow it explicitly, especially in the case of a kit-built engine, and we have found that to be the case in too many instances. You’ll likely be hearing more from us on that subject in the future as we look for ways to increase adherence to our documentation and improve builder’s awareness of VW maintenance considerations.

Once again, I would invite everyone to take a look at the insightful report of Sonex accident statistics from Ron Wanttaja. While kit manufacturers like Sonex and others along with people like Ron and organizations like EAA work tirelessly to continue the downward trend in homebuilt accidents, the homebuilt aircraft builder and pilot, including those buying used homebuilt aircraft, are the key to all of this.

Sonex aircraft are very well-mannered airplanes with good low-speed handling characteristics. Make sure that you invest time in getting to know it better. If you are still building, KEEP FLYING while you build. If you have not already done so, utilize the EAA Flight Test Manual in your familiarization with your Sonex aircraft, even if you purchased it already flying. Fill-in those empty spaces in your Sonex Flight Manual with the data you collect. Practice stalls in your Sonex as-part of that familiarization and ongoing recurrency, and practice engine-out scenarios as-well. As many on this discussion group have said, FLY THE AIRPLANE at all times in order to achieve the safest outcome.

There will be more posts coming from us related to FWF troubleshooting, best practices during engine break-in and other topics, so stay tuned.