Accident Statistics: Certified vs. Non-Certified Engines

Ron Wanttaja wrote in message . ..
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."

Does this take into account things like modified Lycomings? We have
an O-360 with an Ellison TBI. It isn't a certified engine, but it's
not an auto conversion or rotax or something either.

On 11 Jan 2004 07:47:52 -0800, (Bob Martin) wrote:

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."

Does this take into account things like modified Lycomings? We have
an O-360 with an Ellison TBI. It isn't a certified engine, but it's
not an auto conversion or rotax or something either.

The database engine description column does not provide indication of
accessories, but the narratives mention non-standard components if they
have anything to do with the accidents. I suspect the NTSB investigator
probably lists "Lycoming" if the engine is *mostly* Lycoming...like in the
case of one Seawind crash, where the plane had one standard mag and one
non-certified electronic ignition.

I went through the 1998-2000 accident reports and did my own assessment as
to causes. Allow me to summarize the causes for those cases involving a
loss of power due to mechanical problems. Here's an explanation of the
categories:

"Undetermined": Loss of engine power for unknown causes
"Engine Internal": Failures in the interior of the engine, such as a valve
or connecting rod
"Fuel - System": Problems in the fuel system from the tank caps to the
gascolator, inclusive
"Fuel - Engine": Problems "forward" of the gascolator (or "aft" if it's a
pusher).
"Ignition": Problems with the ignition, wires, or plugs
"Drive system": PSRU or drive shaft
"Oil System": Oil pumps, oil lines, etc.
"Carb Mech": Mechanical problems at the carburetor

I've lumped the Lycoming and Continental numbers together. The percentages
are the ratio between the cases with the particular cause, and all the
non-fuel-exhaustion loss-of-power incidents involving that engine.

Be advised that the results below do NOT necessarily reflect the NTSB
"Probable Cause" for the accidents. In loss of power accidents, the NTSB
investigators often list the cause of the engine failure as a secondary
cause, and fault the pilot for not being able to land the airplane
separately. I read the reports (yes, over 800 of them) and made my own
determination. The data below includes both the primary and secondary
causes.

------------------------------------------------------------------------
Results:

(As ever, this displays better if you've got your reader set to a
fixed-spaced font)
Lyconts Auto
Undetermined 31.5% 25.9%
Engine Internal 20.4% 29.6%
Fuel - Engine 3.7% 0.0%
Fuel - System 25.9% 14.8%
Ignition 1.9% 14.8%
Drive system 1.9% 3.7%
Oil System 7.4% 0.0%
Carb Mech 7.4% 7.4%
Carb Ice 9.3% 0.0%
Cooling System 0.0% 3.7%

Sample Size 54 27

Note that the sample size is low enough that one anomalous event runs the
percentages higher.

Ron Wanttaja