Which system must aircraft certificated in the standard classification include?

Aircraft certificated in the standard classification are required to have a positive means of shutting off the fuel to all engines. This is an essential safety feature that ensures that in the event of an emergency, such as a fuel leak or fire, the pilot can quickly and effectively stop the fuel flow to all engines.

This system is critical for maintaining control over the aircraft's fuel system and mitigating risks associated with fuel-related incidents. It allows pilots to manage the aircraft's systems proactively and ensures safer operation by preventing the engines from receiving fuel if needed.

Other options, while they may contribute to an aircraft's overall performance or operational efficiency, do not fulfill the same critical need for safety in the standard classification. Therefore, the necessity of a positive means of shutting off the fuel system stands out as fundamental in aircraft design and certification.