Complex sentence: The accident triggered a wave of inquiries over the operations of regional airlines in the United States; it was the first fatal accident of a commercial airliner in the U.S. since Comair Flight 5191, which crashed in August 2006 with 49 fatalities.
Split into simpler sentences: The accident triggered a wave of inquiries about the operations of regional airlines in the United States. It was the first fatal airline accident in the U.S. since the crash of Comair Flight 5191 in August 2006, with 49 fatalities.