An assessment of risk and safety in civil aviation - Industrial Centre

46 M. Janic / Journal of Air Transport Management 6 (2000) 43}50
could save the aircraft despite severe icing (Owen,
1998).
Strictly, mechanical failures result from human errors
made whilst constructing, producing and maintaining
the equipment. Such errors can accelerate metal fatigue
and other failures in aircraft components. The
crashes of Comets are one example (Owen, 1998) and
another was the problem of an Aloha Airlines B737 in
1988 when the aircraft suddenly lost part of its cabin
roof and sides during #ight. In this latter case, investigators
found the main cause of cabin crack was metal
fatigue due to the frequency of take-o!s and landings
of the aircraft and corrosion due to frequent #ying in
salt air. Design problems lead to modi"cations in
equipment. The main cause of a crash of a DC-10 near
Paris in 1974 that killed 346 people was weakness in
the aircraft's doors and di$culties in to checking if
they were closed. The result was stronger and better
designed doors. The crash of a DC-10 at Chicago in
1979 happened due to engine failure. The event resulted
in stricter rules and procedures covering engine
maintenance and a review of take-o! speeds (Stewart,
1974).
The root-cause of many disasters originates in maintenance
workshops and in the factories where vital
components and systems have been produced. An
example "re on a British Airtours B737 at Manchester
Airport in 1985. Thermal fatigue, or weakening of the
metal by constant heating and cooling during an engine's
life produced a crack in the combustion during
the take-o!. The section separated from the engine and
hit the port wing fuel tank spilling of fuel on a hot
engine. Subsequently, cracks were found in other engines
of this type (Owen, 1998).
Hazardous weather such as thunderstorms and frontal
systems can cause troublesome winds, rain, snow,
fog, and low ceilings that may pose safety concerns
at all stages of a #ight. In particular, strong windshear
developing near airports can make #ying
di$cult because of its rapid change in speed and direction
and because of a loss of lift in certain conditions.
The crash of an Eastern Airlines B727 during
approach at New York's Kennedy Airport in June
1975 o!ers a case study of the dangers involved.
During the period 1970}1987 the US National Transportation
Safety Board identi"ed low-altitude wind
shear as the factor causing or contributing to 18 commercial
aircraft accidents; seven were fatal resulting in
the loss of 575 lives. The development of sophisticated
This example illustrates the importance of experience and training
in reducing the probability of an accident (Kuhlmann, 1981). However,
education and training of aviation sta! is expensive which poses problems
at time when airlines are under pressure to control costs (Dose,
1995).
weather reporting, forecasting and detecting systems,
onboard and ground-based, have reduced this type of
threat.
Terrorist actions are highly correlated with political
and economic tensions in the world. A typical example
was the crash of a B747 on 23 June 1985 due to
a suspected bomb explosion. After the crash security
measures at high risk airports were strengthened.
Such acts have also initiated the introduction of new
technologies and security procedures that are intended
to prevent an illegal entry onto the aircraft and to
detect the presence of weapons being taken onboard.
(Rosenberg, 1987).
Military and semi-military operations have also resulted
in accidents. One example was the crash of
a Korean B-747 over Sakhalin Inland killing 269
people. Due to navigational error the aircraft
deviated from its prescribed course and entered
Soviet airspace and #ew over a prohibited area.
After several warnings, the aircraft was shot down by
a Soviet missile. The event stimulated improved coordination
of civil and military aviation (Stewart,
1994).
Human errors can be reduced by training and the
structuring of air tra$c patterns so as to avoid excess
stress. Factors such as hazardous weather, mechanical
faults, sabotages and military operations would seem to
be more random and less easily dealt with. This does not
mean the system is unsafe. Safety should be considered
with respect to the base causes of accidents. If accidents
occur due to known and avoidable factors, the system
should be considered as unsafe. Otherwise, if accidents
occur for unknown and unavoidable reasons, the system
should be considered as safe.
4. A methodology for assessing the risk and safety
In civil aviation, risk has been assessed as the probability
of the occurrence of an air accident in terms of two
aggregate indicators, the accident rate and the fatality
rate. The probability of an air accident is very low making
it a di$cult and complex task to properly explain,
locate, and manage overall aviation safety. There is also
the need to consider the impact of policy on di!erent
impacted groups such as users, service operators (airlines,
airports, air tra$c control), aviation and non-aviation
professional and non-professional organizations and
public (Kanafani, 1984).
Two approaches for assessing risk and safety are considerd.
The causal approach looks at the number of
accidents and number of fatalities, the scale of the system's
output during a given period and other relevant
characteristics that are seen as relevant causal variables.
The number of accidents, deaths and injuries per unit of