Which of the following statements is true about Law Enforcement Officers (LEO) on flights?

The correct statement about Law Enforcement Officers (LEO) on flights is that they may be armed and travel as regular passengers. This reflects the policy that allows qualified law enforcement officers to carry their service weapons while flying, provided they comply with specific regulations set by the Transportation Security Administration (TSA) and the airline's own policies. This arrangement allows them to perform their duties even while off duty, enhancing security on flights without being disruptive to other passengers.

The idea that they are usually visible to passengers is more contingent on the situation and the discretion of the officer; they may choose to remain discreet. The statement that they must always be armed is inaccurate, as there are occasions when they may fly unarmed, depending on departmental guidelines or personal choice. Lastly, while they contribute to security, the primary responsibility for in-flight security rests with the airline's crew and specialized security personnel. Thus, while LEOs can play an important role, they are not solely responsible for maintaining in-flight security.