Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 92; Flight Crew Total 3437; Flight Crew Type 500
Distraction; Situational Awareness
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Aircraft Aircraft Damaged; Flight Crew Overcame Equipment Problem; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport
Aircraft
I took off on and made a left 270 to 1;500 feet MSL as directed to cross over ZZZ airport midfield and then vectors to 020.  As I rolled out on heading and ZZZ called the frequency change at 1;800 feet to Approach; the rear latch on my Glasair Super II Pilot side door failed and slid out of the latched position and back up inside the door. I immediately grabbed the door handle and held it cross body to keep the door from opening in flight and subsequently departing the aircraft. (The Glasair gull wing door is known for departing the aircraft and possibly striking the tail in flight if it opens fully). Thankfully the forward latching pin stayed engaged enough to hold the door in place with my having grabbed the handle and slowing the aircraft enough that the air stream stopped pulling it outward (I slowed from 140 kts indicated to approximately 90 kts indicated). At this point I made a right turn back towards and right downwind for the XX runways. I explained the situation with Tower.  They cleared runway and cleared me to land.  I was able to maintain a slow enough speed and descended from 1;800 feet to the runway without further incident.  I taxied off as directed and into a run up area; where I was able to shutdown; explained the situation to Ground Control; retrieve my tool kit and manually reset and lock the pilot side door for flight.  I was then able to take off and fly back to ZZZ1 without incident.Upon Further investigation once back home; I found that the resin block that held the rear latching pin and guide in place had completely dislodged inside the door and caused the rear latching pin to slide up into the door instead of into the latch housing into the aircraft frame.  This lack of closure was not evident until slipstream was fast enough to pull the door from its recess (approximately 130 kts) and cause it start to dislodge from the aircraft body.  The repair will be to use vinyl ester resin and cabosil filler to glue the metal latch guide back into place inside the door frame; so that the latch cannot slide into and up inside the door frame.
Pilot flying Glasair Super II encountered unlatched cockpit door after takeoff.