On May 1, 1998, at 1430 central daylight time, a Cessna 150M airplane, N459U, was destroyed upon impact with the ground following an encounter with a downdraft while in the traffic pattern near Levelland, Texas. The flight instructor sustained minor injuries and the student pilot was not injured. The airplane was owned by a private individual and was being operated by Levelland Aviation of Levelland, Texas, under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the instructional flight for which a flight plan was not filed. The local flight was originating at the time of the accident. According to the operator, the airplane departed from runway 17 to practice takeoffs and landings in the traffic pattern. The flight instructor reported that after turning crosswind, while the engine was still operating at full takeoff power, the airplane encountered a severe downdraft, resulting in a rate of descent exceeding 1,000 feet per minute, which the flight instructor stated that the airplane was not capable of out climbing. The flight instructor turned the airplane to avoid the north-south high tension power lines to the east of the airport, as he maneuvered the airplane towards a plowed field to the east-southeast of the airport. The flight instructor further stated that he reduced the engine power prior to impacting the soft plowed field perpendicular with the 14-inch high rows. The airplane impacted the ground on a northeasterly heading in the landing attitude with the flaps in the retracted position. The nose landing gear collapsed and the airplane nosed over coming to rest in the inverted position. The operator stated that virga and dust devils were observed on all quadrants near the time of the accident. While responding to the accident site, the FAA inspector also observed numerous clouds which were producing virga and downbursts by evidence of the dust and dirt being blown in localized areas, below or adjacent to the cloud formations. In a previous flight, the operator also experienced "strong up and downdrafts due to the highly unstable weather pattern." The density altitude was calculated by the investigator-in-charge at 5,600 feet. The 20 year old flight instructor, who is a citizen of India, had accumulated a total of 400 flight hours. The 88 hour student pilot receiving instruction was a citizen of Saudi Arabia. The operator stated that both were very proficient in the English language. Examination of the wreckage by the FAA inspector revealed that the engine assembly, with the propeller still attached, separated from the airframe. The nose landing gear was torn off the fuselage and the vertical fin was crushed. The tail section of the airplane separated from the fuselage aft of the cockpit. The 1976 model Cessna was equipped with shoulder harnesses for both occupants, and they both reported wearing them at the time of the accident. The airplane's ELT was found in the armed position, and was activated by the ground impact.