An American Airlines flight bound for New York City from San Francisco was grounded on Thursday after someone called the police and said there was a bomb on the plane. The FBI has confirmed that two people—a man and a woman who had been sitting in the back row, according to one passenger—were taken off the jetliner in handcuffs. For the most part, though, passengers remained calm and were removed from the aircraft to be sent back through security. TSA spokeswoman Suzanne Trevino said in a statement, “All passengers are safe and, out of an abundance of caution, TSA requested the plane be moved to a remote location.” In response to a disconcerted passenger’s tweets, American Airlines, via its Twitter feed, wrote, “Hang in there. The authorities are taking care of things.” The FBI has called the threat "non-credible."