On August 15, 1998, about 1830 eastern daylight time, a passenger was seriously injured when a Firefly AX-9 hot air balloon, N3141C, landed in Brookhaven, New York. The certificated commercial pilot and five other passengers were not injured. The balloon was not damaged. Visual meteorological conditions prevailed for the local sightseeing flight. No flight plan had been filed for the flight conducted under 14 CFR Part 91. The pilot reported the winds were from the south and light. He departed on a short flight, which was reported as uneventful. He performed a "standup" landing in an open field. He reported that he had instructed the passengers to flex their knees during the landing to absorb any shock of touchdown. During the approach to landing, he instructed one passenger to hang onto the structure in the basket, or to him, during the landing. The passenger elected to hang on to the pilot and upon touchdown, lost her grip and sat down on the bottom of the basket. The pilot reported that during the landing, he flexed his knees as was normal with him. When he realized a passenger was injured, he called for an ambulance. The injured passenger reported the balloon flight was nice until the "crash landing." She reported the pilot told the passengers that, "he had to get down in a hurry", and instructed her to put her arms around him and, "hang on because they were going to hit hard." After touchdown, which she described as hard, she sat down on the bottom of the basket. At the same time, her right foot, which was against the fuel tanks, did not change from that position and she heard the bones in her ankle crunch. There was no apology from the balloon pilot after the landing. Prior to leaving the balloon, she had some champagne, and then was transported via ambulance to a local hospital. The injured passenger reported that she was the only one who fell down, but added that some of the other passengers were bruised. She said her foot was against a canister in the basket and she could not move back. She did not remember it being windy when the accident occurred. Another passenger in the balloon reported the, "balloon ride was wonderful until it became a disaster." She said the balloon, "came down real hard, bounced, [and] came down hard again." She said the injured passenger fell down upon landing, and her foot got caught on a fuel tank. The injured passenger did not have anything to hang onto, as the basket was crowded. She hung onto the pilot's waist, and after she fell, she was in pain. The passenger did not remember the pilot saying anything prior to the landing, and was surprised that the balloon bounced after it touched down. Another balloon pilot reported he was above and to the side of the accident balloon when it landed. It looked like a short field landing to an open field. The landing looked normal and not hard. The winds were 5 to 6 knots. According to medical records of the injured passenger: "Examination shows a fracture, dislocation of the ankle with fracture seen through the lateral and posterior malleoli with dislocation of the foot seen posteriorly along with posterior displacement of the fracture fragments. Remainder of bones and joints are intact." The pilot reported that the basket was certificated for 10 occupants. The accident was reported to the Safety Board by the injured passenger's attorney on November 1, 1999.