COMMUTER LTT RETURN LAND WHEN CABIN DOOR WARNING LIGHT CAME ON JUST AFTER TKOF.

Narrative

ON TKOF; JUST AFTER LIFTOFF (AND WELL AFTER V1); AS THE CABIN BEGAN TO PRESSURIZE; THE CABIN DOOR WARNING LIGHT ILLUMINATED. THE F/O (PNF) TURNED BACK TO CHK THE DOOR HANDLE; IT HAD MOVED ABOUT 3' TOWARD THE OPEN POS. WE DEPRESSURIZED THE CABIN AND THE F/O ATTEMPTED TO RESECURE THE DOOR FROM HIS SEAT. HE WAS UNABLE. WE NOTIFIED ATC; MADE LEFT TFC AND LANDED UNEVENTFULLY ON OUR DEP RWY. THE CABIN DOOR WARNING SYS HAD BEEN DEFERRED; STATING THAT THE DOOR UNSAFE INDICATION WOULD ILLUMINATE AT 6.0 PSI DIFFERENTIAL. THE SYS HAS NO INDICATION OF THE POS OF THE LOCKING MECHANISM WHICH LOCKS THE HANDLE; AND SUBSEQUENTLY THE LATCHES IN PLACE; ONLY IF THE LATCHES ARE EXTENDED. IN ACCORDANCE WITH THE MEL; THE LATCHES WERE VISUALLY INSPECTED BY THE F/O BEFORE STARTING ENGS; AND THE DOOR WARNING LIGHT HAD GONE OUT. AFTER OUR UNSCHEDULED LNDG; RAMP PERSONNEL NOTICED THE DOOR HANDLE WAS IN THE UNSAFE POS AS WE TAXIED IN. THE YOUNG LADY WHO CLOSED THE DOOR BEFORE TKOF (WHO IS TRAINED IN ACFT RAMP OPS AND PROCS ON SECURING THE DOOR) COULD NOT 'GET ENOUGH STRENGTH TO FULLY CLOSE THE HANDLE' AND LEFT IT 1/8-1/4' FROM BEING FLUSH. THAN HANDLE MUST BE FLUSH FOR THE LOCKING PIN TO ENGAGE. HER HEIGHTH MAY HAVE PREVENTED HER FROM PROPERLY CLOSING THE DOOR. THIS ACFT IS NOT TO BE TOWED W/O THE DOOR CLOSED AND LATCHED--MUCH LESS FLOWN. A NOTE OF INTEREST--THE MAINT CLIPBOARD HAS A NOTE ON THE FRONT IN DYMO-TAPE: 'HAVE RAMP PERSONNEL CLOSE DOOR FROM OUTSIDE.' I GUESS WE CAN'T CLOSE IT THEN IN FLT. REMEDY--A DEVICE TO INDICATE IF THE LOCKING PIN IS ENGAGED; MORE TRNING FOR RAMP PERSONNEL; AND DON'T ABUSE THE MEL. ALSO; FIX THE DOOR--NO NOTES ON THE CLIPBOARD.