Complex sentence: The use of a more powerful engine has incresed the aircraft's maximum speed and rate of climb, but has made the aircraft capable of stalling, while aircraft built to the original specifications were incapable of stalls.
Split into simpler sentences: The use of a more powerful engine has incresed the aircraft's maximum speed and rate of climb, but has made the aircraft capable of stalling. Aircraft built to the original specifications were incapable of stalls.