On January 29, 1998, at 0455 hours mountain standard time, a Piper PA-34-200T, N47744, collided with a horse on the landing roll at the Chinle, Arizona, airport. The aircraft sustained substantial damage and the pilot and flight nurse were not injured. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The air ambulance flight had transported a patient to Flagstaff, Arizona, and was returning to Chinle as a 14 CFR Part 91 positioning flight at the time of the accident. The pilot reported to an Federal Aviation Administration inspector that animals frequently enter into the boundaries of the private airport through a gate meant for people's use. Prior to landing he over flew the field at 500 feet agl to verify that the runway was clear, and that both the runway lights and aircraft landing lights were on. The pilot reported that, "It was a very dark night, [and] the moon was not out." On the landing roll, he saw a horse just in front and slightly to his right so he made a left turn to get around it. As he straightened the airplane, a second horse appeared approximately 50 feet straight ahead of him. The pilot further stated that, "I didn't have time to react and we hit the horse with the left wing just left of the engine at about 70 knots." After impact, the airplane deflected to the left towards the fence that surrounded the airport. The pilot pressed the right rudder and brake but entered into a left skid. The left main landing gear then collapsed and the left propeller impacted the ground several times before the nose of the airplane came to a stop.