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Study Shows Aircrew Errors Cause Most Fatal Accidents

Fri, Oct 31, 2008 — David Evans

Articles

Warning systems avert collisions with terrain

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Over a ten-year period, about 850 people were killed annually in airline crashes worldwide, according to a new study of accidents by the UK’s Civil Aviation Authority (CAA). The study goes by its abbreviated title, CAP 776.

The worldwide rate of 0.49 fatal accidents per million hours flown is considerably higher than the same rate in the U.S., where there were no fatalities in 2007 and only two fatal accidents in 2006 (killing 50). Over 8 million hours and more than 7.5 billion miles were flown in each of those years; in this context, the accident rate in the U.S. was phenomenally good.

The CAA study provides a good overview of the accident record and trends over the past decade. The executive summary and selected illustrations follow:

The study looks at 283 fatal accidents over a ten-year period.

“The main risks to large public transport airplanes are identified through an analysis of worldwide fatal accidents, which is a task carried out annually by the CAA Accident Analysis Group (AAG). The output of the AAG forms a key part of the CAA Safety Planning process in that these main risks are assessed for their relevance to the UK aviation system and, where appropriate, safety interventions are identified to mitigate them. These safety interventions can be found in the CAA Safety Plan.

“This document summarizes a study of AAG analyzed worldwide fatal accidents to jet and turboprop airplanes above 5,700 kg [12,500 lb] engaged in passenger, cargo and ferry/positioning flights for the ten-year period 1997 to 2006. The style and content of the document are similar to the previous Global Fatal Accident Review (CAP 681). The main findings of the study are listed below.

“1. Worldwide Fatal Accident Numbers

“1.1     There was a total of 283 worldwide fatal accidents, which resulted in 8,599 fatalities to passengers and crewmembers onboard the aircraft. The proportion of aircraft occupants killed in these fatal accidents was 69%.

“1.2     There was an overall decreasing trend in both the number of fatal accidents and fatalities, although there was more fluctuation in the number of fatalities.

“1.3     The approach, landing and go-around phases accounted for 47% of all fatal accidents and 42% of all onboard fatalities. Take-off and climb accounted for a further 30% of the fatal accidents and 29% of the onboard fatalities.

“2.        Worldwide Aircraft Utilization

“2.1     In the ten-year period from 1997 to 2006, the number of flights flown increased by 17%, which equated to an average annual growth of 1.5%. The equivalent values for hours flown were 31% for overall growth and 2.8% for average annual growth.

“3.        Worldwide Fatal Accident Rates

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Fatal accidents involving passenger flights were fairly evenly split between jets and turboprops. However, those involving cargo and ferry/positioning flights were far more biased towards turboprops and business jets respectively.

“3.1     The overall fatal accident rate for the ten-year period 1997 to 2006 was 0.79 fatal accidents per million flights flown or 0.49 when expressed as per million hours flown.

“3.2     There was a decreasing trend in both the overall rate of fatal accidents and onboard fatalities.

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Number of fatal accidents 1997-2006 broken down by phase of flight.

“3.3     On average, the fatal accident rate for turboprops was three times that for jets, based on flights flown, and nearly seven times greater when using hours flown as the rate of measure.

“3.4     On average, the fatal accident rate for aircraft with maximum take-off weight below 15 tons [30,000 lbs] was twice that for aircraft with maximum take-off weight above 27 tons [54,000 lbs], based on flights flown, and over four times greater when using hours flown as the rate measure.

“3.5     On average, the fatal accident rate for cargo flights was six times greater than for passenger flights (applicable for both rate measures).

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25% of fatal accidents worldwide occurred in Africa.

“3.6     The fatal accident rate for African operators was over seven times greater than that for all operators combined and over 30 times greater than that for North American operators, which had the lowest fatal accident of all the regions.

“4         Factors and Consequences

“4.1     Two-thirds of all fatal accidents involved a flight crew related primary causal factor and 7% involved an aircraft related primary causal factor.

“4.2     The most frequently identified primary causal factor was ‘Omission of action/inappropriate action,’ which was [identified] in 22% of all fatal accidents. This generally related to flight crew continuing their descent below the decision height or minimum descent/safety heights without visual reference, failing to fly a missed approach or omitting to set the correct aircraft configuration for take-off.

“4.3     Three-quarters of all fatal accidents involved at least one flight crew related causal factor and 42% involved at least one aircraft related causal factor.

“4.4     The most frequently identified causal factors were ‘Omission of action/inappropriate action,’ ‘Flight handling’ and ‘Lack of positional awareness in air,’ which were [identified] in 39%, 29% and 27% of all fatal accidents respectively. ‘Flight handling’ tended to be associated with inadequate speed, pitch attitude and/or directional control, often following an engine failure, resulting in the aircraft stalling.

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Top-five causal and circumstantial factors associated with CFIT accidents.

“4.5     These three causal factors were also the most prominent in the previous Global Fatal Accident Review. However, ‘Lack of positional awareness in air’ was involved in proportionally fewer fatal accidents in this study, which reflected a decrease in the proportion of Controlled Flight Into Terrain (CFIT) accidents.

“4.6     The most frequently identified circumstantial factor was ‘Non-fitment of presently available aircraft safety equipment,’ which was [identified] in 33% of all fatal accidents. The majority of these related to non-fitment of the latest Terrain Awareness and Warning Systems [TAWS].

“4.7     ‘Post crash fire’ and ‘Loss of control in flight’ were the two most frequently identified consequences, each appearing in approximately 40% of all fatal accidents. ‘CFIT’ was the third most common consequence, accounting for 25% of all fatal accidents.

“4.8     Compared to the previous Global Fatal Accident Review, ‘Post crash fire’ and ‘Loss of control in flight’ were involved in proportionally more fatal accidents, while ‘CFIT’ was involved in proportionally fewer fatal accidents.”

(The full CAA study, “Global Fatal Accident Review 1997-2000,” may be viewed at www.caa.co.uk/application.aspx?catid=33&pagetype=65&appid=11&mode=detail&id=3198)


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