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PASSENGER AIRCRAFT EVACUATION SYSTEMS

After unexpectedly running out of fuel, the A310 was forced to crash-land at Schwechat airport, Vienna. The pictures of the widebody aircraft lying on its belly near the runway with its undercarriage broken off were seen all around the world. The pilots had brought off a masterly achievement in guiding the powerless aircraft to such a gentle touchdown that no one was injured. The cabin crew evacuating the crashed plane quickly and without panic, and in only a short time all the passengers had slid down the escape chutes into safety.

Oxygen masks, life jackets, escape chutes, lifeboats and so on - everyone has heard of these. Yet the safety instructions which are printed on cards in front of all passengers when they take up their seats and the flight attendants' safety briefings are often ignored. Frequent flyers know their way around and do not feel they need to pay close attention to the demonstrations. Passengers who are afraid of flying on the other hand, after already feeling uneasy, are made to feel even more enough uncomfortable during the presentation on how the life-saving equipment works. Hardly anyone believes that these masks and jackets could really make the difference between life and death, yet the emergency landing in Vienna showed just how effective they are.

It was the American James Boyle, experienced at building balloons since 1929, who originally invented a simple and effective life jacket for USAF pilots during the second world war. These jackets were mass-produced from 1940 and went down in history under the nickname of "Mae Wests", after the famous Hollywood beauty of the time. Soon afterwards he founded the company Air Cruisers, and it was not long before his firm had developed the first escape chutes, as the propeller aircraft of the time towered so high above the ground due to the huge size of the engine propellers that jumping down from above could cause serious injury.

The first of these chutes, still quite modest by today's standards, was installed in the "Columbine", the Presidential aircraft Air Force One, in the 1950s. Fortunately it never had to be used, but the advertising effect was so great that the company soon developed into one of the leading suppliers of life-saving equipment to the international aerospace industry.

A second manufacturer of such safety equipment was the Pacific Inflatables Co. (PICO), which in 1971 revolutionised aircraft evacuation systems. Up to then passenger planes had still been equipped with primitive chutes, and on overseas flights rubber dinghies were also carried. PICO now broke new ground by equipping the DC-10 with a novel kind of inflatable chute which simultaneously functioned as a stable life raft.

Meanwhile, a third large competitor, BF Goodrich, had become established in the market. This company had a long-established rubber business and for many years had been doing very well as a tyre manufacturer and also as a supplier to the aerospace industry. Suddenly, out of the blue at the end of the 1960s the company received an order from Boeing to equip Boeing 747's from 1970 with cold gas-filled neoprene chutes for use over land, and from 1975 the jumbo jet was also fitted with the combination life rafts. Despite a steady increase in the numbers of units produced, the market could no longer sustain three competitors, and in 1985 BFGoodrich took over PICO. Since then BFGoodrich and Air Cruisers have been the only manufacturers of life-saving equipment for all classes of passenger aircraft.

For some time now it has been mandatory to carry such equipment on board, and work continues unabated on the further development and enhancement of the technology. For example, the requirements placed on a combination chute/raft are quite demanding: it must be capable of enabling passengers to exit the aircraft at the rate of 60 per minute, of withstanding external temperatures of between -40-o and +70-oC and of being deployed in winds of up to 40km/h. On top of this, it must be lightweight, fit into the smallest possible space, incorporate life-saving equipment for use at sea and be packed in such a way as to require virtually no maintenance.

No single design is effective on more than a handful of aircraft models, so the manufacturers are constantly having to adapt to each new aircraft type that enters service.

Thus, for example, the designers of the future super jumbo Airbus A3XX will have to work closely with the suppliers of life-saving equipment in order to comply with the legal requirement that every aircraft, irrespective of size, can be completely evacuated within 90 seconds. At first sight this might appear a hopeless task for a double-decker aircraft that seats 555 passengers.

But the British Fire Safety Engineering Group has already demonstrated that it is actually quite feasible. For the past six years they have been developing the airEXODUS software, which is based on the data contained in the Aircraft Accidents Statistics and Knowledge Database. 55 aircraft accidents, 1295 reports from those involved, 320 analyses of fatalities and 110 statements from crew members are held on this database.

It is now possible to simulate on the computer the sequence of events that will occur on an emergency landing. The consequences of a fire on board the A3XX took 14 hours to analyse, even though the location, distance apart and size of the emergency exits had been previously specified. The software uses 25 different criteria to assign passengers to four different categories, such as age, size or sex. In this way it is feasible that in the future simulations with such software could dispense with today's requirement for a complicated series of tests to be carried out using real human subjects, during which on average 6% of participants actually sustain an injury.

Despite the odds, in the computer simulation an A3XX was completely evacuated within 66 seconds. However, it is unlikely that the aircraft will be granted certification without trials using "real" passengers, as the air safety authorities only trust the software up to a certain point.

Meanwhile, a new study by the UK Civil Aviation Authority shows up the inadequacies of safety planning for passenger aircraft: apparently passengers are now significantly larger than at the time when the current regulations governing the distance between seats came into force. It is not just a matter of in-flight passenger discomfort, but adherence to these regulations is actually jeopardising safety on board. Yet if inter-seat distances are increased, fewer passengers can be carried, and that means less profit for the airlines. If safety is to be the top priority, then this bitter pill will have to be swallowed.

From page 90 of FLUG REVUE 10/2000