Law enforcement and fire officials were investigating a potential threat on a plane at Denver International Airport, but police later said the threat was unfounded.

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.

As low-budget airlines face a downturn, Frontier is launching 15 new routes, including a direct flight from Salt Lake City to Southern California.