ATX CABIN DOOR OPENED AFTER TKOF.

Narrative

JUST AFTER TKOF FROM RWY 23 AT MOLOKAI ARPT ON A FLT TO MAUI; AT ABOUT 350-400' AGL; THE UPPER DOOR OF THE MAIN CABIN ENTRANCE DOOR POPPED EITHER PARTIALLY OR FULL OPEN (I COULD NOT TELL FROM WHERE I WAS SEATED) AND A CORRESPONDING DOOR OPEN CAUTION LIGHT CAME ON THE ADVISORY PANEL. THERE WERE NO CTL PROBS WITH THE ACFT; SO I KEPT THE AIRSPD DOWN; CONFIGURED FOR LNDG AND ADVISED THE PAX TO REMAIN CALM AND THAT WE WERE CIRCLING BACK AROUND FOR A LNDG. AFTER AN UNEVENTFUL LNDG AND TAXI AND SHUTDOWN; I INSPECTED THE DOOR FOR DAMAGE. I FOUND NO DAMAGE AND THE MECHANISM FOR LOCKING THE DOOR WORKED FINE; SO I RELOCKED THE DOOR; TOOK OFF AND FLEW UNEVENTFULLY TO MAUI. THIS IS THE ONLY ACFT IN OUR FLEET THAT HAS A LOCKING LEVER THAT TRAVELS THROUGH ABOUT A 135 DEG ARC TO EXTEND THE DOOR'S LOCKING BAYONET FITTINGS (ALL THE REST HAVE D-RING HANDLES). THE LEVER DOES NOT PROVIDE A GOOD MEANS OF PULLING INWARD ON IT WHILE ROTATING IT TO THE LOCKED POS--AS DOES THE D-RING HANDLE. THUS; IT WAS EITHER NOT PROPERLY LOCKED (DOOR WARNING LIGHT WAS CHKED OUT AND ADVISORY LIGHTS PUSHED TO TEST BEFORE TKOF CHKLIST); OR A PAX MAY HAVE MOVED TO ANOTHER SEAT AND BRUSHED AGAINST THE LEVER ENOUGH TO UNLOCK IT. RECOMMEND THAT THE LOCKING LEVER BE CHANGED TO THE D-RING CONFIGN. SEE DRAWING OF LEVEL MECHANISM (I THINK THE LOCKED/UNLOCKED POS ARE REVERSED).