What happens when the MECH button on the CALLS panel is pushed?

When the MECH button on the CALLS panel is pushed, it activates an external horn which will continue to sound until the button is released. This functionality is designed to ensure that the warning or alert is noticeable and can be sustained for as long as necessary to communicate the urgency of the situation, thereby providing effective notification to ground personnel or anyone outside the aircraft.

The design choice to have the horn sound for the duration that the button is held down allows for flexibility in emergencies, enabling the flight crew to use the horn effectively until immediate communication is achieved or the situation is resolved. Other options suggesting fixed durations, such as 15, 30, or 45 seconds, do not accurately capture the operational intent of providing continuous audible warnings as needed.