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.

Police confirmed that officers cleared the Frontier plane that landed in Denver on Monday from Seattle, and that “the threat appears to be unfounded at this time.”

Frontier Airlines has announced four new flight routes from Denver International Airport to begin this October.