A small fire in the brake system just ahead of the jet’s takeoff prompted the evacuation of 173 passengers and six crew members, the authorities said.

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 to Denver was evacuated upon landing after reports of what were thought to be threatening notes. Bomb units and police officers were sent to the flight when it landed in Denver, but the notes were later revealed not to be concerning, according to CBS News.