AN SMA PLT RETURNED AND LANDED AFTER HIS CABIN DOOR CAME OPEN INFLT.

Narrative

AFTER DEP FROM MEM INTL IN SMA ACFT; I LEVELED AT 3000 FT MSL AS CLRED BY ATC. SHORTLY AFTER; THE FRONT COCKPIT CABIN DOOR POPPED OPEN. AT THIS TIME I WAS IN AND OUT OF THE BOTTOM OF A RAGGED OVCST. SINCE THE NOISE LEVEL WAS TOO HIGH TO MAINTAIN ADEQUATE COM WITH ATC AND I DID NOT WANT TO GET INTO IMC WHILE TRYING TO SECURE THE DOOR; I ELECTED -- WHILE STILL VMC -- TO DSND APPROX 300 FT TO STAY BELOW THE CLOUDS. AFTER SLOWING DOWN; GETTING THE DOOR PARTIALLY SECURED AND ADVISING ATC; I WAS VECTORED BACK TO MEM ARPT AND LANDED WITHOUT INCIDENT. THE CAUSE OF THE PROB WAS THAT THE DOOR DID NOT FULLY LOCK PRIOR TO TKOF. THIS IS A CHKLIST ITEM AND IS NORMALLY DONE AFTER ENG START AND RECHKED PRIOR TO TKOF. HOWEVER; THE DOOR SEAL HAD BEEN RECENTLY REPLACED AND COMPLETE LOCKING WAS MORE DIFFICULT THAN EXPECTED. ALTHOUGH I DEVIATED FROM MY ALT IN THE TCA WITHOUT CLRNC; I BELIEVE THIS WAS THE SAFEST ACTION; I.E.; TO STAY IN VMC RATHER THAN HAVING TO FLY INSTS; SLOW AND RECONFIGURE THE ACFT AND CLOSE THE DOOR; ALL AT THE SAME TIME.