Ron Wanttaja wrote in
news
A while back, I posted the result of a cursory look at the accident
statistics for aircraft powered by auto engine conversions. It *was*
an awful shallow pass, and at the time I promised to look into the
issue deeper.

I have since obtained the NTSB accident databases for the years 1998,
1999, and 2000, and am ready to provide more exact figures.

The nice thing about the accident databases is that they usually
describe the type of engine that powers the aircraft. Unfortunately,
the FAA registration database is a lot more vague. A lot homebuilts
are merely described as having experimental engines; a number don't
even have an entry. So we can't do the classic "x% of auto
engined-airplanes have accidents every year vs. y% Lycont-powered
planes."

Instead, we can take another tack: We can catalog the number of each
type of engine in accident aircraft, then take a look at how often a
loss of engine power was a factor in the accident. The figures don't
include cases where the cause was traced to carburetor ice or the
pilot running out of fuel.

Presentation of data:

The "ENGINE" column describes the general category of the engine, one
of four types:

"Certified" Engines include Continentals, Lycomings, Franklins,
Pratt
and Whitney, Jacobs, Vendeyev, LOM, and Walter.

"Auto" Engines include those identified as Subarus, Suzukis,
Fords,
Volkswagens, Revmaster, Chevrolet, GM, Mazda, Honda, Stratus, or NSI.

"Non-C/4" are four-cylinder, non-certified, non-auto conversion
engines. They include the Rotax 912 series, the Jabiru, and the
Rotorway.

"Two-Stokes" include Rotax 4* and 5* series, Yamahas, KFMs, Hirth,
2SI,
and Cuyuna.

The next column is "ACC". This is the number of accidents in the
1998-2000 timeframe that involved each category of engine

"PCT" is the percent of the total accidents where that category of
engine was installed.

"LOP" are the number of accidents where loss of engine power was
involved.

"LOP%" is the percentage of cases where accidents involving aircraft
mounting that category of engine suffered an engine-related loss of
power.

---------------------------------------------------------
The Results:

ENGINE ACC PCT LOP LOP%
------ --- --- --- ----
Certified 332 51% 57 17%
Auto 95 15% 27 28%
Non-C/4 70 11% 13 19%
Two-Strokes 134 21% 46 34%

Of primary interest here, I think is the percentage of accidents where
a loss of engine power occured...17% for certified-engine-powered
planes, vs. 28% for auto-engine conversions. Two-strokes were even
higher; almost a third of their accidents involved a power failure.

It's interesting to note the non-certified four strokes are doing
practically as well as the certified engines. The Rotax 912/914
series alone does even better... a LOP% value of 13%.

An interesting side note: Lycomings outnumbered Continentals by
nearly four to one....

Ron Wanttaja





I wonder what these figures really tell us.... I believe type of
accidents as a percent of total accidents really can't tell us anything.

What if accidents of other types (the rest of the %) where actually
lower in homebuilts with auto engines?

What if things like icing, or VFR into IMC was more prevalent in
certified aircraft, skewing the engine related numbers into a lower
percent...

It would also be my guess (and only a guess it is) that a greater
percentage of homebuilts with non-certified engines are fair-weather
daytime fliers, and therefore more likely to not be as subject to night
perception problems, flying into mountains.. etc., therefore reducing
the total number of "other" type accidents and making the engine-out %
higher.

I also wonder if homebuilts on average experience less other mechanical
type failures such as control linkage, etc., since the builder is
intimately familiar with the workings of the aircraft.

IMHO the ONLY valid percentages would be total registered auto engine
powered aircraft vs engine-out accidents compared to the same in
certified... now I do realize that those figures would be near
impossible to compile short of contacting every single person with a
registered aircraft that the engine type is not listed in the FAA
database... and even more accurate would involve total hours… ok, that's
highly improbable…..


Please note the above is based on no research whatsoever...I am likely
completely off base since I'm new to aviation in general.. ;-)


ET

Future student pilot and future Sonex builder.