Environmental Engineering Reference
In-Depth Information
Accident/crash probability
This concerns the annual probability of a crash occurring near a given airport. As avi-
ation is a safe mode of transport per kilometre travelled, in order to achieve a statis-
tically valid basis for a risk calculation at a particular airport this value is derived
from historical information regarding crash rates per aircraft type from a number of
world airports, which is then multiplied by annual aircraft movements at the airport
under study (NATS, 2000). At Schiphol Airport, for example, risk analysis shows an
accident probability of 0.4 x 10
-6
per movement for take-off and 0.21 x 10
-6
for
landing (Ale and Piers, 2000).
Crash location model
This models the probability that the accident aircraft will end up at a particular
location. A number of approaches have been developed for the crash location model
using either runway referenced, traffic route referenced or non-dependent location
probability models.
Crash accident consequence model
This determines the size of the crash area and the proportion of people likely to be
killed within this area. For third-party risk analysis, the only consequences considered
are fatal injuries to people on the ground. Consequence models should correctly reflect
the influence of the aircraft, impact and environment-related parameters that affect
the accident consequences (Ale and Piers, 2000).
Once defined, the risk contours can be used to control development in the areas
surrounding the airport. While it is likely that there will be mandatory inclusion of
third-party risks for environmental impact statements for airports, at present the risk
assessments have only been applied where airports are undergoing reassessments regard-
ing expansion plans. In these cases, the following measures are usually proposed for
the UK:
•
In the inner-contour zone where the level of risk is in excess of 1 in 10,000 per
year (10
-4
), existing housing and other developments occupied by third parties
for a high proportion of the day should be removed.
6
Ale and Piers (2000)
report that within the Schiphol risk assessment, a 5 x 10
-5
risk contour is used
for this inner zone.
Where the risk is between 10
-4
and 10
-5
per year, new or more extensive devel-
opment in this area, which would result in a higher density of human occupa-
tion, such as new housing and most types of new non-residential development
including multistorey car parks and transport terminals, will be restricted. How-
ever, some non-residential development with a low density of human occupa-
tion, such as warehousing and surface-level car parking, may still be approved.
•
The removal of existing development from outside the 10
-4
contour is unneces-
sary because, on applying constrained cost-benefit analysis, the costs of doing
so would be greater than the benefits.
•
