What is indicated by the red arc on the cabin differential pressure gauge?

The red arc on the cabin differential pressure gauge indicates the range that is beyond the maximum allowable differential pressure for safe operation of the aircraft, which is set at above 6.6 PSI. When the differential pressure exceeds this limit, it can indicate potential issues with cabin pressurization, which could lead to structural strain on the aircraft and compromise safety.

Being aware of this limit is crucial for pilots and crew to maintain safe flight conditions and to ensure that effective pressurization controls are in place. Understanding the significance of the red arc ensures that operators are vigilant about monitoring cabin pressure during flight and taking corrective actions when necessary, such as descending to a lower altitude if cabin pressure is not adequately maintained.