Final answer:
The MAN ALT selector, when selected UP, causes the outflow valves to OPEN, allowing air to escape from the cabin and decrease the cabin pressure. This ensures a safe and comfortable flight when climbing to a higher altitude.
Step-by-step explanation:
The MAN ALT (Manual Altitude) selector is used in an aircraft to control the outflow valves, which regulate cabin pressure. When the MAN ALT selector is selected UP, it causes the outflow valves to OPEN. This allows air to escape from the cabin, decreasing the cabin pressure. As a result, the aircraft can climb to a higher altitude without causing discomfort or harm to the passengers and crew.
For example, imagine you're in an airplane flying at a lower altitude. If the cabin pressure remains the same as the outside pressure while climbing to a higher altitude, the passengers and crew may experience discomfort and potentially even physiological issues. By opening the outflow valves, the MAN ALT selector allows the cabin pressure to decrease gradually as the aircraft ascends, ensuring a safe and comfortable flight.