On September 2, 2003, about 1340 eastern daylight time, a passenger was seriously injured while attempting to board a Fairchild Dornier 328-300, N413FJ, operated by Atlantic Coast Airlines as flight 6204. There were no injuries to the 2 certificated pilots, 1 flight attendant and 20 passengers. Visual meteorological conditions prevailed for the scheduled passenger flight. An instrument flight rules (IFR) flight plan had been filed, for the flight that was conducted under 14 CFR Part 121. According to the passenger, she raised her left foot to reach the first step on the airplane, and then retracted her foot to place it on the ground. In the process, she lost her balance, fell, and fractured her left wrist. According to the manager of safety for Atlantic Coast Airlines, the airplane was equipped with an airstair door on the left side of the fuselage forward of the wing. The stairs were an integral part of the door. The height of the first step on the airplane measured between 10.25 inches and 12.75 inches above the ground, depending up the baggage and passenger load. The space between steps, after the first step was 6.75 inches. In addition, the handrail was on the right side of the stairs, and did not extend to the length of the stairs. In addition, the manager of safety for Atlantic Coast Airlines reported that their station manual required a person to be present at the bottom of the stairs when passengers were deplaning, but there was no requirement for a person to be there during passenger boarding.