Known as chevrons, these serrated trailing edges were developed to tackle one of commercial aviation's biggest environmental challenges: aircraft noise. The result was one of the most recognizable features of several modern Boeing aircraft, although it ultimately came with compromises that would shape future engine development. When these two flows meet behind the engine, the large difference in velocity creates turbulent mixing, which is one of the primary sources of jet engine noise. Related Why Did Boeing Build The 737 MAX With Engine Chevrons? The GE9X is also the largest commercial aircraft engine ever developed, featuring a fan measuring 134 inches (3.40 meters) in diameter.