Between December 1963 and January 1964, Yeager completed five flights in the NASA M2-F1 lifting body. An accident during a December 1963 test flight in one of the school's NF-104s resulted in serious injuries. After climbing to a near-record altitude, the plane's controls became ineffective, and it entered a flat spin. After several turns, and an altitude loss of approximately 95,000 feet, Yeager ejected from the plane. During the ejection, the seat straps released normally, but the seat base slammed into Yeager, with the still-hot rocket motor breaking his helmet's plastic faceplate and causing his emergency oxygen supply to catch fire. The resulting burns to his face required extensive and agonizing medical care. This was Yeager's last attempt at setting test-flying records.
