Retro-fitment of an oxygen system in a transport aircraft of Indian Air Force: Decompression chamber trials to assess system functionality

Abstract

The aeromedical concerns of sudden onset hypoxia and rapid decompression are an omnipresent threat to flight safety when flying over 10,000 ft. The concept of Time of Useful Consciousness (TUC) provides the aircrew a window to correct his predicament. The issues of hypoxia are mitigated in transport aircraft with cabin pressurization. However, the requirement of an oxygen system in these aircraft is considered essential in an emergency in case of cabin failure of cabin pressurization or rapid decompression, despite adequate TUC, as it provides immediate succor from anxiety, and subtle performance decrements, especially in VIP carriage or casevac roles. With this background, a requirement for retro-fitment of a functional oxygen system of a small transport ac of Indo-German origin into a pressurized medium-lift cargo aircraft of British Origin was envisaged. Toward this, ground-based simulator trials were conducted on the oxygen system to assess its functionality before undertaking flight trials in the aircraft. The assessment consisted of the ground trial of the test oxygen system in the Explosive Decompression Chamber with three experiment protocols. The experimentation involved exposure to a simulated altitude of 15,000 ft for 25 min and rapid decompression from 7000 to 15,000 ft. Physiological parameters, endurance, and flow of oxygen in the system were evaluated. The trial results indicated that the physiological parameters (heart rate, respiratory rate, oxygen saturation [SpO2], and end-tidal carbon dioxide [EtCO2]) were within normal limits during the entire duration of exposure to 15,000 ft and decompression from 7000 ft to 15,000 ft. In addition, the physiological parameters were also within normal limits during exposure to 1 min of simulated hyperventilation. Neither any subjective or objective symptoms of hypoxia were observed nor any appreciation of increased breathing resistance reported by the subjects. The endurance of the system in terms of delivering continuous oxygen flow at 15,000 ft was assessed to be 73 min. From the trials, it was inferred that the oxygen system in a single crew configuration could be used satisfactorily up to the operational ceiling altitude specified for the subject aircraft.