F R 1 - 9 7

Home | Update | Latest Issue | Gallery | FR Profile | Datafiles | FR 1/97 JUST IN CASE: SAFETY IN THE AIRLINER CABIN by Heinrich Hemker Airliner are the safest means of transportation. This is a result of the extreme efforts which have been made in order to eliminate all possible faults one can think of. Still, aviation must calculate with the unexpected. Several emergency systems which are installed in the aircraft are designed to minimize the risks coming from this incalculable factor. The pressurized cabin is the most important life-support means in the airliner. It ensures enough partial oxygen pressure to allow cruising levels which would normally be endangering the passenger's lives. In the event that the pressurization of the cabin fails, for example, due to damage to the aircraft skin, passengers as well as flight crews have emergency oxygen available. Two systems are used. The cockpit crew has oxygen masks available which must fulfill some strict requirements. For example, the crewmember must be able to put the mask on with just one hand. The French company Intertechnique is manufacturing a widely used equipment which features a sophisticated technology. The mask straps are combined with elastic tubes that inflate and stiffen if the mask is taken from its hold, such allowing to comfortably put the mask over the head with one hand. Once the grip on the mask is released, the tubes deflate and their elastic characteristics ensure a perfect fit. In flight altitudes above 12500 m, one pilot must always carry a oxygen mask for safety reasons. The oxygen for the cockpit crews is supplied from separate oxygen tanks which are refilled on the ground. The oxygen masks used in the passenger cabin are of a less sophisticated design. In case of a loss of pressurization, the emergency masks are released from the overhead compartments. Once the passenger has grabbed his mask and activated the system by pulling on the tube, a chemical reaction is started in the oxygen cartridge. This cartridge contains sodium chloride which dissolves into table salt and oxygen. The oxygen supply lasts for approximately 15 to 22 minutes, enough time for the pilots to accomplish an emergency descent into lower altitudes with enough oxygen partial pressure. Other issues, which the aircraft might run into, include engine problems. The loss of one engine is no problem even for a twin-engine aircraft. The power of one engine is enough to safely reach the nearest airport. In the case that both engine's power is lost most airliners are equipped with an auxiliary power unit (APU), so there is enough energy available for controlling the aircraft. Still, the engineers went a step further and designed another fall-back option. Certain aircraft are equipped with so called ram air turbines (RAT) which generate the necessary hydraulic pressure to control the aircraft. In normal flight conditions, the RAT is retracted into the fuselage like the landing gear. Only when the release mechanism is activated from the cockpit, the turbine is extended by a gas pressure jack and starts to turn in the airflow. The US company Sundstrand is a renowned manufacturer of such systems, making different models for Boeing and Airbus aircraft. A new development, which Sundstrand is currently working on for use with the next airliner generation, features RATs that are installed in the tips of both wings. With the system in normal mode, the profiles of the turbines are aligned in flight direction and are working like outboard fins, such reducing the induced drag and the fuel consumption. In the emergency mode a clutch is released and the airflow is powering the turbines which now supply energy to the aircraft systems. Since this cleverly designed system drives to shafts, it would be possible to power a hydraulic motor and an electric generator. In today's systems the emergency electric supply is generated by redundant electric supplies from the engine generators and the APU system. Even if the electric fails and even if the accumulators are empty, this ensures that a minimum of instruments is still powered, including one radio. Airliners are equipped with a set of emergency instruments that work absolutely independent from all other aircraft systems. A fire extinguishing system is a standard equipment of airliners. All areas at risk are fitted with sensors, either thermostatic switches or contact loops. While cockpit and cabin are equipped with manual fire extinguishers, other sections, especially the engines, are fitted with a fire extinguishing system. Each turbofan and APU is covered by sensors which signal a fire to the cockpit. The crew can then activate the extinguishing system. While being banned on the ground, Halon is still used in aviation as the main fire extinguishing means. The gas is dangerous to the ozone layer but is a very effective means of extinguishing fires. Among others, NASA is currently working on a substitute for this gas. Until new products are available, the airlines are well advised in doing like Lufthansa, which is already the number one in recycling Halon very effectively during the regular checks of the extinguishing systems. Each door and emergency exit is equipped with an emergency chute in case that the airliner must be evacuated as fast as possible. The French company Air Cruisers International is making this equipment for Airbus aircraft. Each chute must prove its function in a practical test before it is delivered to the Airbus plant. Manufacturer and certification authorities are still looking for more possibilities to counter any thinkable event. The US company Puritan Bennett Aero Systems is now offering video cameras which can be mounted at strategic locations throughout the aircraft. A monitor in the cockpit allows the crews to look at normally inaccessible areas of the aircraft during flight. From page 56 of FLUG REVUE 1/97 Home | Update | Latest Issue | Gallery | FR Profile | Datafiles | FR 1/97 Copyright 1996 by Motor-Presse Stuttgart. All rights reserved. Last updated December 11, 1996