The original L-39 is a proven and safe plane but it is classified as experimental and not certified aircraft. Experimental aircraft have specific operating limitations and are subject to different FAR’s. The TFE-731 engine has a phenomenal track record. Since the engine was introduced in 1972, over 13,000 engines have been built, flying over 100 million flight-hours. However, while the 731 is a certified engine, once installed in an Albatros, it is not. It does however, have to comply with ADs, cycle limits and must make rated power to fly.