Complex sentence: They flew on 15 February and 16 April 1994, testing the Arrius 2B and Pratt & Whitney Canada PW206B engines, the older and less powerful Allison Model 250 powerplant having been rejected.
Split into simpler sentences: They flew on 15 February and 16 April 1994, testing the Arrius 2B and Pratt & Whitney Canada PW206B engines. The older and less powerful Allison Model 250 powerplant had been rejected.