SMA'S CABIN DOOR OPENS INFLT. ACFT RETURN LAND AT DEP ARPT. ALTDEV NOTED BY ALERT APCH CTLR IN THE ARSA.

Narrative

AFTER DEPARTING HSV; UPON REACHING APPROX 3500 FT MSL DURING CLBOUT; THE ACFT CABIN DOOR POPPED OPEN UNEXPECTEDLY. FOLLOWING THE MANUFACTURER'S RECOMMENDATIONS; I SLOWED THE ACFT TO 90 MPH; OPENED THE SMALL WINDOW TO THE L OF THE PLT'S SEAT; AND WITH SOME EFFORT WAS ABLE TO GET THE DOOR CLOSED; BUT NOT PROPERLY LATCHED. UNFORTUNATELY; DURING THIS TIME (ABOUT 1 MIN) THE ACFT DSNDED TO 1600 FT MSL (ABOUT 1000 FT AGL); AND I DID NOT WANT TO INCREASE AIRSPD OR ENG PWR GREATLY; FEARING THAT THE ADDITIONAL AIRFLOW AND VIBRATION MIGHT LEAD TO THE DOOR RE-OPENING. HUNTSVILLE APCH CTL NOTICED MY LOSS OF ALT; INQUIRED AS TO THE REASON FOR THE DSCNT; AND CLRED ME FOR RETURN TO THE ARPT. DURING RETURN; I MAINTAINED 1600 FT MSL AND ABOUT 110 MPH; LNDG SUCCESSFULLY WITH 1/2 FLAPS (25 DEGS). THE DOOR WAS CLOSED NORMALLY; APPEARING TO HAVE INCURRED NO DAMAGE; AND THE TRIP WAS THEN COMPLETED WITHOUT FURTHER DIFFICULTIES. ALTHOUGH I DID VISUALLY CHK THE POS OF THE DOOR LATCH PRIOR TO TKOF; IT IS POSSIBLE THAT THE PAX WHO CLOSED THE DOOR DID NOT DO SO FIRMLY ENOUGH FOR THE LATCH TO FUNCTION PROPERLY. ALSO; THE BULB IN THE DOOR LATCH WARNING LIGHT HAD BURNED OUT AND NOT YET BEEN REPLACED. IN THE FUTURE; I WILL GIVE THE DOOR A GOOD SHOVE DURING THE PRE-TKOF CHK; AND CARRY A SPARE BULB FOR EACH OF THE ACFT'S WARNING LIGHTS.