On March 17, 1999, about 1540 Eastern Standard Time, a flight attendant was seriously injured when she fell from the main cabin doorway of a Boeing 737-300, N17321, to the tarmac, at Newark International Airport (EWR), Newark, New Jersey. The airplane, which was operating as Continental Airlines flight 517, was parked at the gate. The 2 pilots, 2 additional flight attendants, and 104 passengers onboard were not injured, and there was no damage to the airplane. Visual meteorological conditions prevailed at the time of the accident. An instrument flight rules flight plan had been filed for the flight, between Newark and Jacksonville International Airport (JAX), Jacksonville, Florida. The scheduled passenger flight was to be conducted under 14 CFR Part 121. The captain stated that the airplane was completely closed and the jetway had been pushed back in preparation for departure. An agent appeared at the end of the jetway, and after the captain opened the cockpit window, the agent asked if two additional passengers could board. The captain agreed to do so, and the agent proceeded back up the jetway to get the additional passengers. The flight attendant was advised of the situation. The captain then made a pre-departure announcement over the public address system, and when it was completed, a passenger came up to the cockpit and advised him that the flight attendant had fallen from the airplane. The captain disembarked the airplane, and remained with the flight attendant until she was put into an ambulance. According to a representative from the airline, the flight attendant could not remember how the fall occurred, and she declined to make a statement. At the time of the accident, the flight attendant had been flying with the company for 4 months. According to the Continental Airlines in-flight manual, under "Door Opening Procedures" for domestic arrivals of narrow body aircraft, the flight attendant was required to disarm and "crack" the cabin door. "'Cracking' is defined as rotating the handle enough to break the seal on the door after disarming the slide." The gate agent would have actually opened the door. If the gate agent had specifically asked for assistance, the flight attendant would then have assisted in opening the door.