Frontier crew members discovered two threatening notes on a flight headed from Seattle-Tacoma International Airport to Denver, according to the airline.

Denver police Monday afternoon confirmed passengers on a flight arriving to Denver International Airport were evacuated due to a threat that "appears to be unfounded at this time."

A Frontier Airlines flight from Seattle was evacuated at Denver International Airport on Monday after crewmembers discovered two threatening notes on board, but police later determined the threat was not credible. Flight 3406 landed safely at DIA around 11:15 a.m., about an hour behind schedule.