Manual pressurization procedures are necessary when which of the following occurs?

The necessity for manual pressurization procedures arises in situations where the automatic pressurization system cannot function as intended, which occurs under specific failure conditions. When both automatic pressurization controllers fail, the system becomes unable to maintain pressurization automatically, making it critical for the flight crew to manually control the cabin pressure to ensure safety and comfort.

Additionally, the loss of all generators can lead to a complete loss of electrical power for the pressurization controllers, similarly requiring manual intervention. Without power, the automatic systems cannot operate, again necessitating manual pressurization procedures.

Therefore, manual pressurization is essential in both scenarios outlined—when both auto pressurization controllers fail and when there is a loss of all generators, which is why the option indicating that either condition would necessitate manual pressurization is the correct choice. This highlights the importance of understanding system redundancy and manual procedures to ensure safety during flight operations.