Complex sentence: The hijackers crashed the aircraft into the western side of the Pentagon at 09:37 EDT, severely damaging it and causing a large fire, and at 10:10 a portion of the Pentagon collapsed.
Split into simpler sentences: The hijackers crashed the aircraft into the western side of the Pentagon at 09:37 EDT. The impact severely damaged an area of the Pentagon and caused a large fire, and at 10:10 a portion of the Pentagon collapsed.