On Sat, 23 Jun 2007 21:11:14 -0000, wrote:

If I buy a used homebuilt, is it possible for me to make big
modifications, such as installing a larger engine, adding long range
fuel tanks, floats, etc., assuming there was an A/P to sign-off on
it? Any FAA approvals required? Is it likely an A/P would be willing
to make major changes like this or is the liability too great?

You have to keep the airplane in strict compliance with its type certificate.

Oh, wait...homebuilts don't HAVE type certificates. :-)

You are allowed to do anything you want, except you should contact the FAA in
regards to the major modifications, since they'll probably want to you repeat
the Phase 1 flight testing.

You don't need an A&P to do the modifications...you can legally do them
yourself, or find some other capable individual. However, since you purchased
the plane, you'll have to let an A&P examine it for an annual condition
inspection at some point. He's not likely to sign the plane off it he doesn't
think the modifications are airworthy, no matter if you've been flying with them
for almost a year.

A&P concerns about liability really depend on the individual.

Ron Wanttaja