Complex sentence: The "60-minute rule" was waived in 1964 for 3-engined aircraft, which opened the way for the development of wide-body, intercontinental trijets, such as the Lockheed L-1011 Tristar and DC-10.
Split into simpler sentences: The "60-minute rule" was waived in 1964 for 3-engined aircraft. This opened the way for the development of wide-body intercontinental trijets such as the Lockheed L-1011 Tristar and DC-10.