Within only a few years, Rotax develops its next top seller, engines for ultra-light aircraft, and secures itself another leading role. Initially using surplus two stroke engines from sluggish snowmobile production and later increasingly its newly-developed four stroke engine, Rotax also finds success in the air. The development of these powertrains presents different challenges than other Rotax products. Aircraft engines must be licensed by the appropriate authorities, requiring further flawless documentation. Safety is also subjected to double the scrutiny – the electrics and hydraulics must ensure trouble-free operation. Rotax overcomes these challenges in record time, and by the end of the 1980s, four out of every five ultralights boast Rotax engines!