If the lav/galley extract fan fails, what happens to the cabin zone inlet duct temperature?

When the lav/galley extract fan fails, the impact on the cabin zone inlet duct temperature is significant in that it results in a fixed temperature regulation at 59°F. This occurs because the environmental control system manages temperature settings based on various inputs, and the failure of the extract fan leads to a situation where the air circulation and temperature control cannot effectively adjust based on cabin conditions.

In normal operation, balanced airflow is essential for maintaining the desired temperature in the cabin. When the extract fan malfunctions, the system defaults to a set temperature to avoid overheating or excessive cooling, hence the regulation stabilizes at this specific temperature point. This mechanism is crucial for preserving passenger comfort and system integrity even when part of the system fails.

The other options present scenarios that imply varying temperature changes or regulation that do not reflect the fail-safe nature of the cabin's environmental control systems during such a failure.