On May 20, 2007, approximately 1500 central daylight time, a single-engine Grumman American AA-5B airplane, N28730, was substantially damaged when it collided with trees following a loss of control while on approach to the Hilltop Lakes Airport (0TE4), near Hilltop Lakes, Texas. The private pilot and his passenger were seriously injured. The airplane was registered to Cyrus Aviation Services, Inc., of Bryan, Texas, and was being operated by the pilot. Visual meteorological conditions prevailed and no flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight. The cross-country flight originated from the Coulter Field Airport (KCFD) near Bryan, Texas, at 1330. The 300-hour private pilot reported that while on final approach to Runway 16 at the Hilltop Lakes Airport, the airplane entered an un-commanded nose down pitch and banked to the left. The pilot added that he responded by applying full power and adding back pressure; however the airplane did not respond and crashed into the trees. The airplane came to rest suspended in the trees. Members of the local volunteer fire department removed trees to gain access to the airplane and "forcibly opened the canopy." Both occupants were assisted out of the airplane. The airplane was equipped with seat belts and shoulder harnesses. They were both being used at the time of the mishap. According to a Federal Aviation Administration (FAA) inspector, who traveled to the accident site, both wings sustained structural damage. The nose wheel, engine firewall, engine mounts, and portions of the fuselage were also damaged. There was no fire. An examination of the engine was conducted on June 8, 2007 by representatives of the National Transportation Safety Board. Examination of the engine 180-horsepower Lycoming O-360-A4K engine did not reveal any mechanical anomalies that could have prevented normal engine operation. The fuel cells were breached; however, the operator reported that the airplane departed the Coulter Field with a full load of fuel, and according to the engine tach, the flight's duration was 36 minutes. According to the aircraft's performance chart, conditions were favorable for the probability of "serious" carburetor icing at glide power. Examination of the airplane and engine revealed that the carburetor heat control was in the "off" or cold position. At 1453, the weather observation facility at Easterwood Field Airport (CLL), located near College Station, Texas, located 31 miles south of the accident site, reported wind from 120 degrees at 9 knots, gusting to 14 knots, visibility 10 statute miles, a scattered cloud layers at 4,900 feet and 10,000 feet MSL, temperature 81 degrees Fahrenheit, dew point 55 degrees Fahrenheit, and a barometric pressure of 30.07 inches of Mercury.