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