In the event of failure of both automatic pressurization controllers, what does a third motor provide?

The correct answer indicates that a third motor provides manual operation of the outflow valve in the event of failure of both automatic pressurization controllers. This detail is significant because, in aircraft systems, the outflow valve is crucial for controlling cabin pressure. When the automatic system fails, pilots require a means to maintain control over cabin pressure manually to prevent any hazardous situation that could arise from inadequate pressurization or potential cabin depressurization.

The manual operation functionality ensures that the crew can still manage the cabin environment, ensuring safety and comfort of passengers and crew. Therefore, having a third motor for manual control provides redundancy and allows for continued operation even in failure scenarios. This capability reinforces the importance of having fail-safe systems in aviation, especially concerning critical systems like pressurization.