Flight 253, Umar Farouk Abdulmutallab attempted to detonate explosives sewn into his underwear. In 2012, the attempted hijacking of Tianjin Airlines Flight 7554 was stopped when cabin crew placed a trolley in-front of the cockpit door and asked passengers for help. American Airlines Flight 11 In the September 11 attacks, crew on one of the hijacked planes went beyond their scope of training by informing the airline ground crew about the events on board. In separate phone calls, Amy Sweeney and Betty Ong provided information on seat numbers of the attackers and passenger injuries. This helped authorities identify them. Cockpit security As early as 1964, the FAA required cockpit doors on commercial aircraft be kept locked during flight. In 2002, U.S. Congress passed the Arming Pilots Against Terrorism Act, allowing pilots at U.S. airlines to carry guns in the cockpit. Since 2003, these pilots are known as Federal Flight Deck Officers. It is estimated that one in 10 of the 125,000 commercial pilots are trained and armed. Also in 2002, aircraft manufacturers such as Airbus introduced a reinforced cockpit door which is resistant to gunfire and forced entry. Shortly afterwards, the FAA required operators of more than 6,000 aircraft to install tougher cockpit doors by April 9, 2003. Rules were also tightened to restrict cockpit access and make it easier for pilots to lock the doors. In 2015, Germanwings Flight 9525 was seized by the co-pilot and deliberately crashed, while the captain was out. The captain was unable to re-enter the cockpit, because the airline had already reinforced the cockpit door. The European Aviation Safety Agency issued a recommendation for airlines to ensure that at least two people, one pilot and a member of cabin crew, occupy the cockpit during flight. The FAA in the United States enforce a similar rule. Air marshal service Some countries operate a marshal service, which puts members of law enforcement on high-risk flights based on intelligence. Their role is to keep passengers safe, by preventing hijackings and other criminal acts committed on a plane. Federal marshals in the U.S. are required to identify themselves before boarding a plane; marshals of other countries often are not. According to the Congressional Research Service, the budget for the U.S. Federal Air Marshal Service was US$719 million in 2007. Marshals often sit as regular passengers, at the front of the plane to allow observation of the cockpit. Despite