"No warning was issued by NORAD HQ," regarding a potential threat to the US, according to Captain Pamela Kunze, the chief NORAD spokesperson.

The Federal Aviation Administration, responsible for the nation's air traffic control system, and NORAD have not responded to CNN's multiple requests for comment on why some pilots were ordered to land and prevented from taking off from multiple West Coast airports on Monday afternoon, citing a "national ground stop."

The NORAD spokeswoman said the normal sequence following the launch was followed: The missile launch was detected, and it was assessed not to be a threat to the continental United States.

The standard practice is for FAA to have a constant liaison in the NORAD ops center, therefore would have been aware of the quick assessment.

LiveATC air traffic control recordings of the Burbank Airport in California detail a controller telling a Southwest flight "there's ground stops all departures, all airports right now.

The message we got is it's until further notice."

Another recording of the control tower frequency in Hillsboro, Oregon, captures the controller telling the pilot of a Cessna to land, saying "we just got a notice that we need to do a national ground stop."

A spokesperson for the San Diego International Airport told CNN the airport "was instructed by Air Traffic Control that there was a national ground stop but shortly after [5-7 minutes] our operations team was told it was lifted."

Other West Coast airports contacted by CNN said they were unaware of the order.

It is not clear why the ground stop was put in place because a statement from US Forces Korea said the test posed no threat to US or South Korean territory or military personnel, but "the missile launch highlights the destabilizing impact of (North Korea's) illicit weapons program."

North Korea conducted what is thought to be a ballistic missile test around 07:27 am local time Tuesday (5:27pm ET Monday), the missile was launched form inland and traveled east and falling into the sea.

US Strategic Command and NORAD uses satellites and radar to track every missile launch around the globe and are able to quickly assess whether a launch poses a threat to the United States.