Final answer:
The CLR pushbutton's function on the ECAM Control Panel is to clear the display of non-critical messages, helping maintain clarity on the display screen.
Step-by-step explanation:
The CLR pushbutton on the ECAM (Electronic Centralised Aircraft Monitor) Control Panel of an aircraft has a specific function. Its primary purpose is to clear the display of non-critical messages. When a pilot or a crew member sees a non-critical message or caution that has been acknowledged and addressed, they can press the CLR pushbutton to remove the message from the ECAM display screen. This helps in managing the display and ensuring that only relevant and critical information is shown, thus maintaining clarity and reducing the risk of information overload in the cockpit.
The other options provided, such as initiating an emergency descent procedure, activating the cabin lighting system, and resetting the engine control unit, are not related to the CLR pushbutton's functionality. Those actions have separate controls and procedures.