On Sun, 11 Jan 2004 19:39:57 GMT, ET wrote:

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?

That was basically the start of this exercise, several months ago. The FAA
registration database lists the type of engine, but for about 3,600
homebuilts, it is either blank or merely lists "AMA/EXPR" for an engine.
That's about 13% of all homebuilts. Many of these are undoubtedly auto
conversions, but most are probably stock Lycomings or Continentals.

My January 6 2004 database shows 113 homebuilts with Ford engines. But how
many of those 3,600 "AMA/EXPR" engines are Fords? If even a twentieth of
them are Ford conversions, that would double the "known" quantity.

In the almost 700 homebuilt accidents in the 1998-2000 time period, the
NTSB records show only one "AMA/EXPR" engine installed on an accident
aircraft. Either those 3,600-odd airplanes aren't flying at all, or the
NTSB investigators are looking at what was *actually* installed under the
cowling.

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.

Heh, heh...you don't think I downloaded 21 megs of accident reports (at 56
kbaud!), read a thousand or so individual reports, and generated about a
gigabyte of databases and Excel spreadsheets for just a RAH posting on auto
engine conversions, do you?

I've just completed an in-depth analysis of homebuilt accident statistics.
In it, I not only determine the causes of homebuilt accidents during the
1998-2000 time period (35 basic accident categories, plus some
sub-categories), but I compare the accident rates for homebuilts to a
representative sample of certified light aircraft (Cessna 172s and 210s,
leaving out accidents occurring during primary training). And determine
the accident rates for first flights and in the test period, as well.

I completed the three-part article just this week. Hopefully, it'll run
sometime in the summer. Since I don't address the engine issues in the
series (I figured three articles was enough) I could post them here without
"stealing my own thunder."

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.

Sadly, no.

Ron Wanttaja