What is the primary responsibility of an ACPO on a flight?

The primary responsibility of an Air Canada Protective Officer (ACPO) on a flight is to carry firearms on board. This role is specialized and critical for ensuring the safety and security of the aircraft and its passengers. ACPOs are trained law enforcement officers who are tasked with protecting the flight in case of a security threat. Their training includes the use of firearms, emergency response protocols, and conflict resolution strategies, all aimed at maintaining a secure environment while airborne.

The other options describe important functions that may be part of the flight crew's duties, but they do not encapsulate the main focus of the ACPO role. Serving meals and assisting with passenger boarding are standard duties carried out by cabin crew, and managing cabin crew falls under the purview of lead or senior flight attendants rather than a specific security role. Thus, carrying firearms on board effectively distinguishes the ACPO's primary duty in the context of flight operations.