Wis. Stat. § 114.18: Aircraft; airworthiness; federal license.

It shall be unlawful for any person to operate, pilot or navigate, or cause or authorize to be operated, piloted or navigated within this state any civil aircraft, unless such aircraft has a currently effective license issued by the government of the United States or has been duly identified by the government of the United States but this restriction shall not apply to aircraft licensed by a foreign country with which the United States has a reciprocal agreement covering the operations of such licensed aircraft, or to a nonpassenger-carrying flight solely for inspection or test purposes authorized by the United States to be made without such license.