The pilot of the retractable landing gear-equipped airplane reported that, shortly after landing the passenger, without his permission or guidance retracted the landing gear. The landing gear retracted, airplane impacted the runway and slid about 600 ft before coming to rest on the runway.

The pilot rated passenger reported that, without the pilot's guidance, he mistakenly raised the gear handle then quickly lowered it again, thinking it was the flap handle. He was attempting to assist the pilot.

The airplane sustained substantial damage to the center wing spar.

The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.