Complex sentence: The Flamingo was designed by de Havilland, lead by their chief designer, as an all-metal twin-engined civil airliner, the first all metal aircraft built by de Havilland.
Split into simpler sentences: The Flamingo was designed by de Havilland, led by their chief designer, as a twin-engined civil airliner. It was the first all-metal aircraft built by de Havilland.