Passenger Supplemental Oxygen Supply: Oxygen Flow Saving Opportunities

Abstract

Maximum cabin pressure altitude is limited by regulation to 2440 m (8 kft) for normal flight. In case of cabin depressurization, the cabin pressure altitude may rapidly increase up to maximum A/C altitude. To protect the passengers from lack of oxygen (hypoxia), the passenger supplemental oxygen supply shall provide per regulation a minimum oxygenation equivalent to 3050 m (10 kft) or 4270 m (14,000 kft) whether the cabin pressure altitude is lower or higher than 5640 m (18 kft). The corresponding airworthiness requirement CS/FAR 25.1443(c) defines the minimum performance in term of oxygen partial pressure in the trachea. For demonstration, international standards have been available (TSO C64a / SAE AS8025) for several decades. More than the oxygen partial pressure in the trachea, the blood oxygen saturation is the most relevant parameter to characterize the level of oxygenation. Current medical instrumentation are available for measuring directly the blood oxygen saturation. This alternative means of demonstration has been systematically studied during a test campaign at the DLR – Institute of Aerospace Medicine in Cologne with human testing in altitude chamber. Different types of oxygen dispensing devices have been tested at different altitudes. Results show that the oxygenation level required by the regulation is achieved with significantly less oxygen than used so far. This is explained by the different efficiency level of oxygen transfer to the blood during the different phases of the breathing process. In other words, it is important to deliver oxygen at the right time, so that oxygen is effectively transferred to the blood and not “wasted” during subsequent exhalation. In the last years, this alternative means of compliance has been accepted by the Airworthiness Authorities. This has opened possibilities to introduce new technologies in oxygen dispensing equipment and to reduce the amount of oxygen to be transported on-board. These different opportunities are shortly presented and discussed.