Complex sentence: In fact most contemporary aircraft were prone to catching fire in the air.The fire hazard was reduced, however, when the pressurised fuel system was replaced by one using wind driven fuel pumps late in 1917, although this was not initially adopted by American built aircraft.
Split into simpler sentences: In fact most contemporary aircraft were prone to catching fire in the air. The fire hazard was reduced, however, when the pressurised fuel system was replaced by one using wind driven fuel pumps late in 1917, although this was not initially adopted by American built aircraft.