Make sure you provide a written bill of sale and add provisions that the paraplane is not working, in what way it is not working, and is sold as is. Nothing can prevent you from getting sued in the future, but that does not mean you will be found liable. Let the buyer beware is the general rule still for most transactions in this state, but full disclosure in writing will help insure you aren't held liable.
To questioners from West Virginia & New York: Although I am licensed to practice in your state, I practice on a day-to-day basis in Massachusetts. I answer questions in your state in areas of the law in which I practice, and in which I feel comfortable trying to offer you assistance based on my knowledge of specific statutes in your state and/or general principles applicable in all states. It is always best, however, to work with attorneys and court personnel in your own area to deal with specific problems and factual situations.