Complex sentence: Prior to the development of GPWS there were an average of over 10 CFIT crashes a year, since the U.S. Federal Aviation Administration required large airplanes to carry such equipment in 1974, the number of CFIT accidents have reduced significantly.
Split into simpler sentences: Prior to the development of GPWS there were an average of over 10 CFIT crashes a year. Since the U.S. Federal Aviation Administration required large airplanes to carry such equipment in 1974, the number of CFIT accidents have reduced significantly.