Hi everyone,
With all due respect, I have made a quick spreadsheet of all the fatal "Sonex" accidents in the NTSB database. The link is here; anyone with the link can view or edit the spreadsheet --
https://docs.google.com/spreadsheets/d/ ... sp=sharingI would like to advance and/or discuss a number of hypotheses:
1. Fatal accidents usually involve loss of power5 out of 8 of the accidents involve loss of power; 2 out of 8 are unknown; and 1 out of 8 is known to have occurred with power available. I would consider this hypothesis well supported.
This does not imply that power failures in the Sonex are not survivable -- proving that would require an analysis of more data, including incidents not reported to the NTSB or the FAA. However, it is clear that, when accidents are unsurvivable, they are likely caused by loss of power.
I honestly have no idea what the prevalence of fatal power-loss accidents says about the reliability of the engines or carbs commonly used on Sonex aircraft. I leave it to those with expertise in the matter to study the issue.
2. Fatal accidents involve stall, potentially with dropped wingAll accidents about which we know some details involve a nose-down attitude on impact. Many include witness accounts of a sharp bank then a dive. I would also consider this hypothesis well supported.
(Note in the data that the probable cause for N75654 says, "It is likely that the pilot, distracted by the loss of engine power, allowed the airplane to enter an unusual attitude, and the tail separated during the pilot’s attempted recovery from the unusual attitude.")
3. Fatal accidents involve low time in type or insufficient trainingThis is something that I actually cannot support or refute with the data I have. I would hope that someone has more data about this.
At issue here, of course, is whether transition training, or some training program, is likely to bump the numbers.
One of the things I do worry about is the "train the other pilot" suggestion. We all think we are perfectly well trained and ready; it's the
other guy/gal who needs to undergo rigorous remedial education, training, and for good measure, should be made to eat spinach every day! :) Yet
somebody is crashing these airplanes.... It is for this reason that I would counsel training as only
part of a solution.
4. Sonex aircraft are touchy during stallThe video posted by
fastj22 at
https://www.youtube.com/watch?v=xP4EAMk-ZAU seems to indicate that the Sonex tends to drop a wing sharply in a stall. Am I correct? If one were to hire an experienced CFI to fly a Sonex as an average pilot would, slightly carelessly, what would they conclude? How would it be different from a C152, say? This would not mean there is anything "wrong" with the Sonex design. It is what it is. But different designs are suited to different use cases.
I do not have experience to evaluate this hypothesis, but I suspect it may be true.
I strongly counsel some such honest, independent evaluation, and would contribute money towards it if it were done.
5. Average non-aerobatic pilots are purchasing and/or building Sonex aircraftSonex marketing emphasizes the low cost and accessibility of their aircraft. They do not market it as an aerobatic aircraft requiring lots of dual training in type. Is the success of the Sonex, in being an easy-to-build, strong LSA that anyone can afford, causing its audience to grow to the point where it is being purchased and/or built by average pilots who expect performance more similar to a Cessna 152/172 or Piper Cherokee?
Clearly we cannot determine how correct this is without a survey of the pilot and builder population.
6. The fatal accident rate can be reduced by controllability improvementsRegardless of engine issues, I claim someone should take whatever would be learned from #4 above and determine if the stall behavior, for
average pilots, can be improved. This might involve test flying with various modifications, including:
Stall warning devices. A suction-type stall horn can easily be retrofitted and plumbed. If someone were to determine the appropriate location, draw up some plans, and compile a list of the parts, it could be an afternoon's job for a builder or mechanic to install the device.
Stabilizing devices. Some devices like stall strips or outboard vortex generators can easily be added in an hour or so by anyone who can operate a measuring tape. Vortex generator kits exist, made of clear plastic that would not ruin the esthetics of a nice aircraft. Someone could perform testing with, say, VGs like
http://www.aircraftspruce.com/catalog/a ... texgen.php, and determine the locations that would help keep the wings level during a stall.
In the end, the only way to "prove" this hypothesis would be to come up with some solutions, throw them out there, and see what happens to the fatal accident rate.
I would strongly counsel trying some solutions based on the known likely causes rather than waiting. It should not be necessary for more people to die.
-----
Personal notesI was part of the team that analyzed the Zenith 601XL failures a few years back, called the Zenith Builders' Analysis Group (ZBAG).
People got really, really defensive. Nothing was done and lots of pilots died.
In the case of the 601XL, it
did actually have some serious problems. The Sonex, luckily, is a well-designed and well-built aircraft. But that doesn't mean that something cannot be done to improve safety.
Ihab