When is a visual inspection of an aircraft required by customs?

A visual inspection of an aircraft is required by customs before all international flights departing the USA to Canada to ensure compliance with customs regulations. This inspection allows customs officials to verify that the aircraft is free of undeclared or prohibited items, as well as to confirm that the flight has the necessary documentation for international travel. This procedure helps maintain border security and prevents illegal activities, such as smuggling.

In the context of the other options, while safety checks and inspections are important for domestic flights and cargo operations, customs inspections specifically focus on international flights to ensure adherence to customs requirements. The discretion of the flight crew does not guide customs procedures, as these inspections are mandated by regulatory authorities. Thus, the necessity for these inspections is particularly emphasized for international travel.