I was having a conversation with someone about experimental vs ultralight rules (we were talking about Mini Max Ultralights), and he mentioned something I did not consider: what if an amateur-built ultralight is modified out of ultralight status, can it be N-numbered?

It led me to think about some other scenarios that I am curious about:

If someone were to build an ultralight, document it, fly it for 300 hours with a Rotax 337, and then replace that with a 503, could they register it at that point?

If they did not document the build (but still built it)?

If they did not modify it over 254lbs, could it still be registered?

If they purchased it with the 337 and a build log, then added the 503?

If they purchased it without a build log, but it is a model that was never built by a factory?



This all spiraled into one last, odd hypothetical, could a pilot, pursuing an ATP license, build a backpack style powered parachute, have it N-numbered, get a Powered Paraglider Sport pilot license and log that time toward total time for 61.159 flight requirements (as long as they meet the other flight requirements?

For the record, I don't plan to do this, and I expect a regional would hesitate before hiring someone with 1500 hours TT with 500 hours logged in a parachute. I'm just curious if it meets the FAA requirements.