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Unusual Losses of Aircraft
Published in Stephen J Wright, Aviation Safety and Security, 2021
The reader must be aware that the service ceiling of the Boeing 777-series aircraft is limited to 43,100 ft. The service ceiling is the maximum safe altitude that an aircraft can fly to when carrying passengers and loads. While it is possible to exceed the manufacturer’s altitude limit, the aircraft will not perform correctly or safely. For instance, the aircraft pressurisation system and ECS (as described in Chapter 4) will not be able to function correctly. The pressure differential between the low-pressure atmosphere outside and the pressure inside the passenger cabin exceeds the aircraft’s structural tolerances. The low cabin pressure will exceed the safe levels for effective respiration (breathing) as pressure will be too low for effective gas transfer in the lungs (i.e. - oxygen absorption and carbon dioxide release in the alveoli). Occupants in a low-pressure cabin environment, such as an aircraft exceeding its service ceiling, will suffer the effects of hypoxia. If not remedied with the return of pressure to safe limits, incapacitation will occur, with death following rapidly.
Oxygen Delivery and Acute Hypoxia: Physiological and Clinical Considerations
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
There are several approaches to avoiding or at least reducing the severity of the problems associated with flying at high altitudes. The simplest, taken by small recreational aircraft, is to restrict flying to altitudes below about 8,000 to 10,000 feet (2,400–3,000 metres). Many commercial and military aircraft fly much higher than 10,000 feet, often above 40,000 feet (12,000 metres). The operating altitude of Concorde was around 55,000 feet (16,750 metres). The reasons include fuel efficiency, reduction of turbulence, air corridor management and tactical considerations. For these aircraft, cabin pressurization is used to reduce the equivalent altitude to which the occupants are exposed. For aircrew and passengers, it would be ideal to keep the pressure in the cabin at sea level, but a compromise has to be reached between human physiology, aircraft design and operational considerations (Ernsting, 1978; Macmillan, 2006).
Cabin systems
Published in David Wyatt, Mike Tooley, Aircraft Electrical and Electronic Systems, 2018
Engine bleed air is supplied into the cabin and then allowed to pass out of the fuselage via outflow valves (OFVs). Most aircraft have a single OFV located near the bottom aft end of the fuselage; some larger aircraft have two. By modulating the position of the outflow valve(s), the pressurization in the cabin can be maintained higher than atmospheric pressure. Modern commercial aircraft have a dual channel electronic controller for maintaining pressurization, with a manual back-up system. These systems maintain cabin air pressure at the equivalent to 2500 m (8000 ft) at high cruising altitudes.
Emergency drug usage during flight and airline safety management for passengers
Published in Journal of Toxicology and Environmental Health, Part A, 2021
An aircraft has a pressurization device for adjusting air pressure in the cabin. As illustrated in Figure 1, oxygen saturation is prevented from dropping significantly until the partial pressure of oxygen (PaO2) in the artery falls below 60 mmHg, thereby protecting passengers from hypoxia to some extent. The air pressure in the cabin is maintained at a level similar to that at an altitude of 5000 to 8000 feet (1524 to 2438 m) (AMA (Aerospace Medical Association) 2008). This indicates that passengers can be transported to their destinations without presenting with physiological abnormalities, as the air pressure in the cabin is reduced by about 25% at this time. The air is rather dry in the airplane with approximately 10% to 20% humidity, and the in-flight temperature is maintained at approximately 23°C to 25°C (www.koreanair.com). However, for passengers in poor physical condition, small changes in air pressure might produce hypoxia, thereby worsening their conditions.
Dripping and Fire Extinction Limits of Thin Wire: Effect of Pressure and Oxygen
Published in Combustion Science and Technology, 2021
Jun Fang, Yue Zhang, Xinyan Huang, Yan Xue, Jingwu Wang, Siwei Zhao, Xuanze He, Luyao Zhao
Figure 2 shows the horizontally placed cylindrical cabin which has a diameter of 40 cm and a length of 40 cm. Compared to the past research (Huang, Nakamura, Williams 2013; Nakamura et al. 2009, 2008a), this cabin volume is three times larger, so the effect of O2 depletion by combustion is much smaller. During the experiment, the cabin is sealed, and the variations of pressure and O2 are less than 1 kPa and 1%, respectively. The ambient temperature is around Ta = 25. The pressure in the cabin can vary from 0.3 kPa to 100 kPa (±0.01 kPa), and the internal pressure is constantly monitored by a pressure gauge. Pure N2 or O2 is mixed with air to slowly feed into the pre-vacuumed cabin until the preset pressure level is reached. The ambient O2 concentration (i.e., mole fraction) varies from 12% to 80%, and an additional oxygen sensor is used to monitor the internal oxygen concentration. During the experiment, there is no external airflow inside the cabin.
Measured moisture accumulation in aircraft walls during simulated commercial flights
Published in Science and Technology for the Built Environment, 2018
Tengfei (tim) Zhang, Guohui Li, Chao-Hsin Lin, Zhigang (daniel) Wei, Shugang Wang
Modern commercial airplanes cruise at a high altitude, at which both the atmospheric pressure and the temperature are extremely low. To sustain human life, aircraft cabins are pressurized, and the cabin air pressure is commonly set at 80% of that at sea level. The aircraft shell is covered with insulation blankets to resist the extreme outside temperature. When an airplane is cruising, large temperature gradients across the insulation blankets cause a net migration of water vapor toward the aircraft shell. Subject to the cabin humidity and thus the dew point temperature, the water vapor may condense into liquid water or freeze directly into ice. At times, the liquid water may evaporate, and the ice may thaw or sublime. In the course of these moisture phase changes, heat release or absorption occurs. The moisture transfer is further complicated by cabin air pressurization or depressurization during flights. Hence, cabin air pressure, relative humidity, and temperature gradients across the insulation blankets may affect moisture accumulation within aircraft walls.