Accident investigation analysis has centered on a single primary cause

Question: In Mr. Phillips’ article the statement was made that accident investigation analysis has centered on a single primary cause when most accidents involve a chain of events. Do you believe that most accident investigations center on a single primary cause?

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Focus on accident prevention key to future airline safety

The safety record of the world’s airlines will decline in the next 20 years unless the industry focuses more on preventing accidents than determining what caused them, according to a study conducted by the Boeing Commercial Airplane Group.

Although the world airline safety record is low and holding steady, about 560 people die annually in fatal crashes, Paul D. Russell, chief engineer, airplane safety engineering for Boeing, said. The studies indicate that airline safety will decline further as more new aircraft are added to the global fleet, he said.

The global airline jet fleet currently stands at 11,507 active aircraft, according to Edmund S. Greenslet of ESG Aviation. He projects the fleet will grow to 18,200 aircraft by the year 2010 and could reach 19,700 by 2014.

Based on projected fleet growth, Russell predicts one jet transport hull loss every week will occur by 2010 unless strong, preventive measures are taken by the industry to reduce accidents. We have to change from concentrating on the cause of an accident to how it could have been prevented, Russell said.

Boeing’s studies are based on transport category, commercial jet-engine aircraft with takeoff gross weights in excess of 60,000 lb. The company has based its conclusions upon accident data from around the world, except for information from China and the former Soviet Union, which is generally not reliable, according to Russell. Traditionally, accident investigation analysis has centered on a single primary cause when most accidents involve a chain of events. As a result, such procedures tend to limit the scope of future accident prevention, he said.

Boeing advocates creation and implementation of prevention strategies designed to interrupt and thwart the accident process before it processes too far, according to Russell. In a detailed study of hull loss accidents from 1982-91, he has identified six principal strategies that affect flight safety. If implemented by the airlines, these would:

·  Address links in the accident chain through the use of probability analysis.

·  Provide a broader objective basis for improvement than conventional investigation procedures by shifting focus from what caused an accident to events that are common in day-to-day operations.

·  Reveal new opportunities for accident prevention that are currently unknown.

·  Allow a number of small improvements that would have a cumulative, positive effect on flight safety.

Russell found that more than 80% of the accidents were caused by the flight crew. In another series of accidents, about 58% were caused by practices or procedures used by the airline; nearly 38% were the fault of air traffic control or an airport facility, 25% were caused by the aircraft and 18% by maintenance actions. Weather caused less than 10% of the accidents.

In its study of hull loss accidents from 1959 through the first six months of 1994, Boeing found that on scheduled flights of 1.6 hr. duration, nearly 70% of the accidents occurred during takeoff and landing operations. Specifically, 24.8% of the accidents occurred during the crucial takeoff and initial climb phases, which represents a mere 2% of total flight time.

Another 43.4% of the accidents occurred during the final approach and landing phases, which account for only 4% of flight time. The U.S. airline system of hub-and-spoke airports tends to increase the possibility of such accidents by virtue of the high number of takeoff and landing operations at such facilities, according to Russell.

Although takeoff and landing operations accounted for nearly 70% of all accidents since 1959, controlled flight into terrain (CFIT) remains the leading cause of airline deaths worldwide, Russell said. During the post decade, an average of 550 people have died each year in CFIT-related accident according to Boeing’s studies.

Analysis of airline hull losses since 1968 shows a clear correlation between CFIT and the use of ground proximity warning system equipment. GPWS warns pilots that the aircraft is too low and in close proximity to terrain. Since 1974-75, when GPWS was implemented by the airlines, 44 accidents have occurred involving aircraft that did not have the system installed, according to Boeing. In 1994, only about 5% of the world’s airline aircraft lack such equipment.

About five or six CFIT accidents occur each year worldwide, and Russell estimates that 75% of these accidents happen during nonprecision instrument approach procedures that lack vertical, or glideslope, guidance. In such cases, a GPWS probably would have provided warning of the impending crash. Boeing’s analysis indicates that slow, incorrect or no pilot response to GPWS alerts was responsible for at least 19 accidents since 1975.

Another important part of Boeing’s prevention strategies concept is an emphasis on regional and cultural perspectives, and in particular how they can affect airline safety. Our data clearly show that there are regional and cultural differences from one part of the world to another that can become factors in an accident scenario, Russell said.

These include flight crew experience, weather forecasting, approach and navigation aids, runway condition and length, whether the route is domestic or international, and cultural differences. The global airline industry must better understand the regional effects on operation of modern jet transports, Russell said. As a result, Boeing is suggesting the formation of worldwide, regional safety councils to address safety issues indigenous to those areas to help prevent accidents.

Boeing’s study of 63 accidents in the U.S. and Canada from 1982-91, for example, showed that prevention strategies applicable to the flying pilot’s adherence to procedures may have been a factor in as much as 41% of the crashes. This compares with 43% of 38 accidents in Europe during the same period, 48% of 47 accidents in Latin America, 32% of 37 accidents in Africa and 52% of 37 accidents in Asia.

Russell also found that strategies linked to improvements in aircraft design, maintenance, air traffic control and basic piloting skills would have played important roles in preventing the accidents. Basic piloting skills, for example, was a factor in 16% of the U.S.-Canada accidents, 34% of those occurring in Latin America, 29% in Africa and 32% in Asia.