Statistical Analysis of Homebuilt Aircraft Engines

[rwanttaja]

I'm trying to wrap my head around the data, and I think I might be over-thinking it.

Is this simply "what kind of engines are in homebuilts" and nothing more? Or with the inclusion of NTSB data is there some other data we can tease out?

Yes, this is basically trying to answer a question in another forum about how many auto-conversions are installed in homebuilts. It should be easy enough to extract from the FAA registration database. But about 4000 homebuilts have an entry that just says, "Amateur-Built/Experimental Engine."

While the FAA database includes a lot of VW and Subaru engines (and a smaller number of Corvairs), it really lists few of the V6/V8 sorts of conversions that seem to get all the press. As you can see above, the January 2016 FAA database shows *no* aircraft powered by Chevrolet engines (other than Corvairs). Yet they can be found in the NTSB database, so the assumption is many of the liquid-cooled Chevy engines are actually listed with the generic AMA/EXP tag.

But...how many of the 4000 are of each type? Are they all auto conversions? Or are folks registering their Continentals and Lycomings as AMA/EXP for their own reasons (such as their not coming up on an AD search....).

So I took those 4000 and compared them to my NTSB accident database. The NTSB almost always lists the engine. So, for about 550 of those 4000, I found accident reports (I did have to be careful it wasn't another plane with the same N-Number). I worked out how many of the 550 were Lycomings, Continentals, etc. As you'll see above, while the FAA database shows no Chevy-powered homebuilts, there were 21 just in that 550-aircraft sample. So, obviously, the number of auto-engine homebuilts were being under-reported, and my analysis was an attempt to extract the true fleet sized.

Btw, if NTSB data is used, there could be more aircraft with a special type of engine installed than registered. One would only have to, through misfortune, make the NTSB records twice with the same aircraft.

Oh, yes, found several of those. Some planes had more than one accident, with a different engine each time.

Ron Wanttaja