Event Description
A pilot reported that approximately 30 minutes after departure, while cruising at 6,000 feet mean sea level, the airplane's cabin door opened in flight. The pilot stated that the temperature dropped, papers flew about the cabin, and the noise became 'overwhelming.' A passenger attempted to hold the door shut but could not secure it.
Pilot Actions
Following the door opening, the pilot diverted to a nearby airport for landing. During the landing, the pilot stated that he 'simply forgot to put the gear down.' The airplane touched down and skidded on its belly.
Damage
The belly landing resulted in substantial damage to the airplane's stringers, formers, and main spar carry through. The pilot reported that there was no malfunction or system failure of the airplane before the accident.