On August 20, 1999, at 0945 central daylight time, a Piper PA-28-151 airplane, N43404, struck a person while taxiing at the Clover Field Airport, Houston, Texas. The person who was struck by the airplane was seriously injured. The certified flight instructor and student pilot in the airplane were not injured, and the airplane sustained minor damage. The airplane was registered to Noles and Associates of Pearland, Texas, and operated by D & N Flying Service of Pearland, Texas. Visual meteorological conditions prevailed for the 14 Code of Federal Regulations Part 91 instructional flight and a flight plan was not filed. According to the flight instructor, the airplane was at the threshold of runway 32L preparing for takeoff, when she and her student witnessed an aircraft accident on the airport. The flight instructor assumed control of the airplane and had the student "announce over the unicom that [they] were taxiing to the scene." As the airplane taxied toward the accident site, the instructor noticed a person, who was the airport manager, walking in the grass adjacent to the left side of the taxiway. The flight instructor reported that "he looked over his right shoulder at us and then turned away as if he saw us and was moving further away from the taxiway." The airport manager then "unexpectedly turned and looked at us (the airplane)" as he changed direction and moved towards the centerline of the taxiway. The flight instructor "braked, pulled the throttle back to stop," and turned the airplane to the right to avoid the airport manager. Subsequently, the left wing of the airplane made contact with the airport manager, and he "slid backwards over the wing surface" and fell onto the taxiway. According to the airport manager, he was fueling an airplane, when he witnessed the aircraft accident on the airport. He stated that he and the pilot of the airplane which he was fueling began to run adjacent to the taxiway towards the accident site. The pilot then stopped and stated that he would go to the terminal and call 911, and the airport manager continued toward the accident site by himself. The airport manager then observed two vehicles, traveling on the taxiway, moving toward the accident site and also observed a helicopter land near the accident site. The airport manager does not recall seeing, hearing or contacting the airplane on the taxiway. The airport manager sustained serious injuries and was hospitalized for three consecutive days. Examination of the airplane revealed that the leading edge of the left wing was dented approximately two feet outboard of the wing root.