The passenger was removed from American Airlines Flight 754 at Phoenix Sky Harbor International airport and transported to a psychiatric facility for evaluation under an involuntary hold, said Sergeant Vince Lewis of the Phoenix Police Department on Thursday.
"We had a situation where right after takeoff a passenger stood and walked to the first class section, where he stood at attention there and refused to take his seat," Lewis said.
"He began making statements that, although they were alarming and threatening in nature, gave the flight crew the indication (of possible mental health issues)," he said, according to Reuters.
Lewis said some of the passenger's comments referenced the attacks of Sept. 11, 2001, and his beliefs about the government.
The flight, which departed Los Angeles International Airport at 8:38 am Pacific Time, carried 150 passengers, three infants and six crew members, and was refueled and allowed to continue on to Philadelphia, a spokesman for American Airlines said.
A spokeswoman for the Phoenix airport declined comment, referring calls to police.