A monitoring system (100) is provided for flight crew members (99), e.g., aviators, pilots, copilots or passengers, of airplanes or aircraft, e.g., airplanes or helicopters of the civil or military aviation, passenger planes in the scheduled or charter service, especially also ultrafast passenger planes. The monitoring system includes a sensor mechanism and a control unit configured to organize a procedure of a measurement-based monitoring of the gas composition of air, breathing air or breathing gases with the sensor mechanism in an airplane or aircraft, and to control or regulate the procedure. A measurement-based detection of gas concentrations is carried out with the sensor mechanism (60).