Causal risk models of air transport - NLR-ATSI

are those that are not immediately apparent but manifest themselves some time after the
accident. Examples of indirect effects are health problems of rescue workers caused by
exposure to toxic substances, or the development of post traumatic stress disorders among
people that have witnessed or were involved in aircraft accidents. The manifestation and
degree of indirect effects is largely governed by social, psychological and epidemiological
factors and requires different knowledge and expertise than estimating direct aircraft crash
effects.
2.2. Risk perception
The definition of safety in the previous section introduces acceptability of risk.
Acceptability of risk is strongly influenced by risk perception. The level of perceived risk
has been found in several studies to be dependent on the degree to which people believe
that risk can be controlled and by whom, trusted or not [Slovic et al 1976, Hale & Glendon
1987]. Voluntary and involuntary exposure to risk is also a main driver for risk
acceptability (Figure 2). Another factor that is related to risk perception and the level of
accepted risk is the chance of multiple fatality accidents [O’Banion 1980, ETSC 1997]. A
fourth factor that plays a role is the time passed since a similar event took place. The more
retrievable the event, the greater its intuited probability. News media’s extensive coverage
of aircraft accidents make them particularly ‘retrievable’. For instance in a 1996 Associated
Press survey, U.S. newspaper editors and television news directors said that the Trans
World Airlines Flight 800 accident 5 was the ‘biggest’ news story of 1996 [Barnett & Wang
2000]. A 1990 study of page-one newspaper articles regarding fatalities in the United States
said that coverage of air carrier accidents in The New York Times was 60 times greater than
its coverage of AIDS, 1,500 times greater than coverage of automobile-related hazards and
6,000 times greater than coverage of cancer [Barnett & Wang 2000]. Events that result in
‘identifiable’ victims have more impact than events resulting in anonymous or ‘statistical’
victims. An accident, such as an aircraft crash, therefore has more impact on public
perception than for instance exposure of large and hence anonymous populations to toxic
substances due to general environmental pollution [Health Council of the Netherlands
1999].
As risk implies possible loss, risk perception is also a direct reflection of perceptions of
value [Brauer 2004]. As such, there are differences in risk perception across cultures and
across time. Accidental death is likely to be more acceptable (to society as a whole) in
regions where the life expectancy is lower than the world average due to ‘natural’ causes of
death such as infectious diseases and famine. A comparison of aircraft accident rates and
gross domestic product across world regions indeed show a strong inverse relation [Roelen
et al 2000c, Visser 1997]. Likewise risk acceptability depends on the benefit associated
with risk exposure. The greater the reward, the higher the risk we are willing to take.
5
On 17 July 1996, Trans World Airlines Flight 800 crashed minutes after take of from John
F. Kennedy International Airport, New York. The cause of the accident was an explosion of
the centre wing fuel tank. The source of ignition energy for the explosion could not be
determined with certainty, but, of the sources evaluated by the investigation, the most likely
was a short circuit outside of the centre wing tank that allowed excessive voltage to enter it
through electrical wiring associated with the fuel quantity indication system [NTSB 2000].
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