Law enforcement and fire officials were investigating a potential threat on a plane at Denver International Airport on Monday afternoon, but police later said the threat was unfounded.Frontier Airlines said crewmembers discovered what they described as "threatening notes" on a plane.

On Thursday afternoon, a ground stop was issued for Denver National Airport, according to the Federal Aviation Administration (FAA).

Passengers were evacuated Saturday from an American Airlines aircraft that was about to take off from Denver International Airport because there was an issue with landing gear.