Complex sentence: On their way to Fargo, North Dakota, Buddy Holly, Ritchie Valens and J.P. Richardson, "the Big Bopper", were killed, boarded an airplane at Mason City, Iowa, along with pilot Roger Peterson.
Split into simpler sentences: On their way to Fargo, North Dakota, Holly, Valens and Richardson were killed. They had boarded an airplane at Mason City, Iowa, along with pilot Roger Peterson.