What does the cabin safety valve protect against?

The cabin safety valve is a crucial safety feature designed to protect the airplane from situations that could lead to structural failure due to excessive differential pressure between the cabin and the outside atmosphere. In normal operation, the cabin is pressurized to maintain a comfortable environment for passengers and crew. However, if a fault occurs that causes the cabin pressure to exceed safe limits, the safety valve opens to relieve this excess pressure. This operation helps to prevent damage to the airframe, ensuring that the aircraft remains structurally sound during flight.

While other options mention issues like cabin altitude and various operational modes, they do not specifically address the role of the cabin safety valve in preventing excessive differential pressure, which is its primary function. This makes it vital for maintaining the integrity of the aircraft structure during various phases of flight.