A PILOT DECLARED AN EMER AND DIVERTED TO NEARBY ARPT AFTER THE CABIN DOOR OPENED. PILOT LANDED AT WRONG; BUT NEARBY AND SIMILAR LOOKING ARPT.

Narrative

APPROX 6 MINS AFTER TKOF FROM ZZZ1 ON A VFR FLT PLAN TO ZZZ2 AND JUST PRIOR TO OPENING MY FLT PLAN WITH THE FSS; I EXPERIENCED THE MAIN CABIN DOOR UNLATCHING AND BECOMING OPEN TO THE AIR STREAM. THIS NECESSITATED AN IMMEDIATE LNDG TO SECURE THE DOOR. WHILE CIRCLING OVER A LARGE LAKE I EXAMINED THE TERMINAL AREA CHART AS WELL AS LOOKED FOR CLOSEST AVAILABLE ARPT FROM THE AIR. SEEING AN ARPT ABOUT 8 MI TO MY NE; WHICH IN GENERAL LAYOUT AND APPROX LOCATION APPEARED TO BE ZZZ; I CONTACTED THEIR TWR; STATED THE NATURE OF MY EMER; AND WAS CLRED TO IMMEDIATELY LAND. AS I APCHED THE ARPT; ZZZ TWR CONTACTED ME AND ASKED MY LOCATION; TO WHICH I REPLIED I WAS ON A VERY SHORT FINAL. THEY THEN ASKED ME THE RWY NUMBER THAT WAS VISIBLE; AND I REPLIED THAT IT WAS NUMBERED '34.' THEY THEN INFORMED ME THAT THE RWY I WAS APCHING WAS LOCATED AT ZZZ3. BEING AT A LOW ALT; APPROX OVER THE THRESHOLD AND WITH AN UNSECURED DOOR; AND NOT HAVING ENOUGH TIME TO CONTACT THE ZZZ3 TWR; I CONTINUED MY LNDG AND TURNED OFF AT THE FIRST AVAILABLE TXWY. I THEN CONTACTED THE TWR AT ZZZ3; STATED THE NATURE OF MY EMER AND WHY I HAD MADE AN UNANNOUNCED INCURSION INTO THEIR AIRSPACE AND LNDG AT THEIR ARPT. THEY DIRECTED ME TO CONTACT THEIR GND CTL; WHO CLRED ME TO THEIR RAMP. AFTER CHKING THE LATCHING MECHANISM OF THE CABIN DOOR AND FULLY SECURING THE DOOR; I PROCEEDED; USING THE NORMAL PROCS TO TAXI TO THE ACTIVE RWY; TKOF; AND RESUMED MY COURSE TO ZZZ2. IT SHOULD BE NOTED THAT BOTH ZZZ AND ZZZ3 HAVE VERY SIMILAR ARPT LAYOUTS; RAMP LOCATIONS; RWY ALIGNMENTS AND ARE BOTH A SIMILAR DISTANCE N FROM THE LAKE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT EVEN THOUGH HE LANDED WITHOUT CLEARANCE AT THE WRONG ARPT; THE FAA HAS SAID NOTHING ABOUT THE EVENT. THE TOWER THAT THE REPORTER WAS IN CONTACT WITH DID NOT RELAY TO THE OTHER TOWER THAT HE WAS APCHING THEIR AIRSPACE. NOTHING WAS EVER SAID. THE DOOR DID NOT CLOSE COMPLETELY BECAUSE THE ACFT WAS BRAND NEW AND REQUIRED MORE THAN NORMAL FORCE TO CLOSE IT COMPLETELY. IN THIS CASE THE R SEAT PAX DID NOT CLOSE THE DOOR WITH ENOUGH FORCE TO CLOSE IT COMPLETELY; THUS ALLOWING THE LOCKING PINS TO SLIDE COMPLETELY INTO PLACE.