A sky marshal or air marshal is a key element in helping to maintain passenger safety and ensuring the security of commercial flights. These persons typically work undercover as part of federal aviation and security authorities. They normally board planes disguised as regular passengers, but are specially trained to intervene if a situation occurs during travel that imperils the plane, crew, and/or passengers. Sky marshals or air marshals typically spend a great deal of time in active commercial air travel and performing related field work.
Air marshals and sky marshals have two key goals. The first is to maintain their anonymity to the maximum extent possible while aboard passenger flights; while the flight crew will typically know if they have a marshal aboard their flight, the passengers are largely unaware. The flight marshal uses his or her ability to blend in with other passengers to maintain a constant watch over activities and passengers within the cabin of the plane. If the marshal thinks he or she has spotted a credible threat to safety, it is his or her job to immediately engage and subdue the threat before it can escalate further.
Because of the nature of this job, most air marshals either have ascended to a high level of civilian law enforcement or performed police and/or security details in active military service. Security agencies will typically look for not only training and aptitude when hiring for this position, but also practical experience in the field, which does provide some preference for persons with a military background.