Running a significance test for Wanttaja's numbers shows no statistically significant difference in the proportion of crashes due to engine failure between traditional engines and rotax engines. It would be interesting to try and get a proportion for failures divided by engines in service from traditional vs. Rotax.
It's difficult to determine, as the FAA records for homebuilt aircraft aren't very consistent as far as engine types. About 13% of the homebuilts in the FAA registry merely give "AMAT/EXP" as their engine type. Another 9% merely say "Bombardier" (or "Rotax") without identifying the model; we cannot tell if it's a two-stroke 582 or a four-stroke 912. When you add in the entries that are merely blank, you end up with
I have taken a stab at estimating the percentage of the AMAT/EXP engines that fall into certain gross categories...
Traditional Certified
Aftermarket Traditional
Foreign Engine
Auto Conversion
Non-Cert 4 Stroke
Two-Stroke
Turbine
....and estimating how many of the model-less "Rotax" entries fall into given models. I have taken the unknown models, compared them to the NTSB database (which usually has precise engine identification) and used those ratios to predict how many of the AMAT/EXP engines fall into the above categories, and how the Rotax unknowns parcel out.
From that, I compute the "Fleet Accident Rate"...what percentage aircraft with each type of engine suffer a crash in a given year.
Here's the cut:
_________Overall_________|_0.76%_|
__Traditional Certified__|_0.65%_|
_Aftermarket Traditional_|_0.45%_|
______Foreign Engine_____|_0.72%_|
_____Auto Conversion_____|_1.19%_|
____Non-Cert 4 Stroke____|_0.77%_|
________Two-Stroke_______|_0.97%_|
_________Turbine_________|_1.57%_|
(Note to Mods:
Please enable the Xenforo table functions....)
Anyway, as you can see, the overall Fleet Rate for EAB aircraft is about .76%/year, while the rate for Traditional Engines is 0.65%.
Rotax 912s fall in what I call the "Non-Cert 4 Stroke" category. As you can see, this category has a 0.77% rate, a bit above the "Traditional Certified" rate.
However... the "Non-Cert 4 Stroke" category is more than the Rotax 912s. It include Jabiru engines, the Rotec engines, etc. In my previous analyses, the Rotax 912s actually come out better than most of the other engines in that category. It is, of course, a lower sample size, so they'll be some inaccuracies there.
Ron Wanttaja
