sentences:  According to aerospace periodical Flight International, the initial production process only took seven months to complete a single prototype.On 27 October 1977, the first prototype (registration "D-EATJ"), powered by a pair of EA871 NSU Wankel engines, made its maiden flight.The EA871 engine installation proved to be troublesome, thus the second prototype ("D-EATI") was furnished with a single Allison 250-C20B turboshaft engine, making its first flight on 31 May 1978.