On Fri, 20 Apr 2007 13:39:55 GMT, Don W
wrote:

Currently there is an "experimental" Bell 206 /
OH58 helicopter on EBAY.

I know that many of the L-39's and other warbirds
are operated as experimentals since they were
never certified in the US.

My question is this:

If you modify a production aircraft and call it
"experimental" what flight and/or use restrictions
apply to that aircraft?

First off, you can't just "call it experimental." The FAA must issue an
airworthiness certificate in the Experimental category, and you must provide
them sufficient justification for them to do so.

As part of the process, you have to declare the purpose of why the aircraft
should be licensed as Experimental. There are about nine sub-categories,
including Research and Development, Racing, Marketing Survey, Exhibition, Crew
Training, and Amateur-Built.

For instance, if you are developing a new engine, for instance, you can mount it
in a Cessna 172 and request certification as Experimental/Research and
Development. Most of the ex-military airplanes like the L-39 get licensed in
the Experimental/Exhibition category. If you built the plane yourself, you can
get it licensed as Experimental/Amateur-Built.

You will need to show to the FAA why the aircraft qualifies to be licensed in
one of these categories. The degree of proof the FAA demands, and the amount of
supervision they impose, depends on which of the sub-categories the airplane
calls under. Experimental Amateur-Built gets the most liberal restrictions,
basically being a lifetime certification. But the person applying for
certification must prove that the airplane was built for "education or
recreation," and that the majority of the tasks were performed by an amateur
builder.

The FAA generally frowns upon people modifying aircraft that have normal
certification. I know a guy who used a 172 as a test bed for a new auto-engine
conversion, but he only received certification in the Experimental/Research and
Development case and his certification was only good for one year at a time.
Every year, about three months prior to expiration, he had to repeat the
application process.

That helicopter on E-Bay is licensed in the Experimental/Exhibition category,
which has become almost as free as Experimental/Amateur-Built. The helicopter
is probably so certified because it's an ex-military aircraft. This still
doesn't give you the freedom to modify it willy-nilly. It really depends on how
the operating limitations are written; likely, the limitations state that the
aircraft must be maintained in accordance to the applicable military tech
documents.

There's only one certification category that allows for easy conversion to
Experimental, followed by the freedom to perform whatever modifications one
wishes: The Special Light Sport Aircraft category.

Ron Wanttaja