Which of these is a locking method for aircraft controls?

A tail rotor lock is a crucial safety feature designed to prevent movement of the tail rotor when the aircraft is not in operation. This locking method is essential because the tail rotor, which helps control the yaw stability of the aircraft, can pose safety risks if it is accidentally engaged or rotated during maintenance or ground handling. By securely locking the tail rotor, ground personnel can safely perform necessary checks and repairs without the risk of injury or damage.

The other choices pertain to different aspects of aircraft operation and maintenance. A lighting system lock refers to ensuring that aircraft lights are correctly set or off, which is unrelated to locking controls. An emergency exit lock typically pertains to securing exit doors to prevent unintended opening during flight, which does not involve control mechanisms. A propeller maintenance report is simply a documentation tool for recording maintenance activities, rather than a locking method for controls.