Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 200; Flight Crew Total 2200; Flight Crew Type 600
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Aircraft Aircraft Damaged; Flight Crew Returned To Departure Airport
Aircraft; Human Factors
Upon departing ZZZ to the south southeast for skydiving operations; I leveled the aircraft to maintain vertical separation from a cloud layer. After leveling the aircraft; I proceeded in the same direction towards an area of no cloud cover. I believe leveling/increasing speed of the aircraft while having the passenger window open in the cockpit; created unequal pressure and caused the sliding door to implode. I immediately reduced speed and began to change direction back towards ZZZ. The imploded door then exited the aircraft; striking the horizontal stabilizer and fell to the surface in pieces into what appeared to be a wooded area. After landing safely I proceeded to scout the area where the debris landed in another airplane. No debris; damage; gatherings or any activity regarding the incident were observed.
Pilot flying DHC-6 aircraft reported cabin door departed inflight.