so here's what little i know.
Aircraft don't depreciate at nearly the rate automobiles do. The do go down in retail value as they get old and/or have a lot of hours on the airframe. Buying a very old aircraft can be a major headache as the cost of making it airworthy can be more than the cost of the plane itself.
Fractional ownership is merely a way of spreading out or sharing the costs of aircraft ownership. You asked "Is it a good business to be in?" Well, what exactly do you mean? Is your friend looking to invest in a light plane? If so, for what purpose? Fractional owners of light planes use them, for the most part, for sport flying or recreational flying. Most of the time the part owners are also pilots (why else would you buy into this sort of thing?) and are entitled to a percentage of the annual available flight hours. They are also responsible for a similar percentage of upkeep. (Fuel, maintenance, tie-down space or hangaring)
Here's a good article that answers some questions about purchasing a plane:
http://www.avweb.com/news/usedacft/182805-1.htmlWikipedia has this on General aviation:
http://en.wikipedia.org/wiki/Light_aircrafthere is an article from "Flying" magazine on the subject:
http://www.flyingmag.com/article.asp?section_id=11&article_id=296A new Cessna Skyhawk, like this one
for instance is going to run $165,000 for a base model.
I suggest your friend just use google and look into it in more detail.
I hope that was a little help