On May 19, 2000, about 1454 eastern daylight time, a Beech 1900C, N154GA, registered to Raytheon Aircraft Receivables Corporation, operated by Gulfstream International Airlines, Inc., as flight 9204, experienced opening of the forward airstair door shortly after takeoff from the Fort Lauderdale/Hollywood International Airport, Fort Lauderdale, Florida. Visual meteorological conditions prevailed at the time and an instrument flight rules (IFR) flight plan was filed for the 14 CFR Part 121, scheduled, international, passenger flight. The airplane sustained minor damage and there were no reported injuries to the airline transport-rated captain, commercial-rated first officer, or 20 passengers. The flight originated at 1452, from the Fort Lauderdale/Hollywood International Airport, Fort Lauderdale, Florida. The captain stated that before departure he reviewed the aircraft flight log and noted that the cabin door warning light was "mel'd". He discussed this with the first officer (F/O) who performed a preflight of the airplane. The F/O reported that after the passengers were boarded, he closed and latched the forward airstair door and verified that it was closed by viewing inside the inspection window and also by viewing the cam sight gauges. He also briefed the passenger in seat 1A, about the emergency procedures pertaining to the door. The captain reported that the flight taxied to runway 9L, was cleared to takeoff, and while climbing through 800 feet mean sea level, he "heard a slight explosion (decompression) and found the forward cabin door [had] blown open." He declared an emergency, returned to Fort Lauderdale, and landed uneventfully. After taxiing to the ramp, he shut down the engines normally and was not aware of damage to the left propeller until after securing the left engine. Postincident examination of the left propeller revealed a gouge in the leading edge of one of the blades and segments of the blade tips of two of the blades were noted to be missing; damage to all four propeller blades was noted. Examination of the forward airstair door revealed that the aft cable assembly was broken and missing an approximate 27-inch segment; several holes were noted in the outer door skin. The door latching mechanism was found to operate normally; no discrepancies were noted. For a period of 1 year from the date of the incident, there were six discrepancies pertaining to annunciation of the forward airstair door. Corrective action was accomplished on all six discrepancies; all were signed off as being operationally checked normal or "OK." On May 8, 2000, the airplane was released in accordance with minimum equipment list (MEL) pertaining to the discrepancy that the forward cabin door annunciator extinguishes without locking the handle; the discrepancy was corrected on May 15, 2000. The same discrepancy of May 8th, was written up again on May 16th; the airplane was again released in accordance with minimum equipment list (MEL). The forward airstair door annunciator remained inoperative for the incident flight and was scheduled to be examined on the evening of the incident date. According to the airline Vice President/Director of Flight Operations (VP/DFO), post incident, the F/O was vague about how to verify that the forward airstair door is locked; he was immediately removed from the flight line and received additional training. He also stated that he interviewed six company F/O's and three of the six reported they would partially open the forward airstair door to demonstrate to the passenger seated in row 1A how to open the door. This would be performed after each F/O verified that the forward airstair door was closed and locked. The VP/DFO reported that the incident F/O stated to him that he did not touch the door but recalled verbally describing the procedure to the passenger sitting in row 1A. The VP/DFO also reported that the company F/O's are taught to verbally describe the door opening procedure to the passenger without operating the door. Post incident, the captain and first officer submitted samples in accordance with the FAA approved drug testing program; both were negative for tested drugs of abuse.