5 Monte Carlo Simulation Results
5.1 Assessed risk levels
Figure 7 shows the accident risk as function of the position of the runway crossing
with respect to the runway threshold. The probability of a collision decreases for
positions of the crossing distances further from the threshold. Figure 7 also shows
the decomposition of the total risk for the cases that the pilot flying of the taxiing
aircraft either thinks to be proceeding on a normal taxiway (without being aware to
be heading to a runway crossing) or where the pilot intends to cross the runway
(without being aware that crossing is currently not allowed). The largest contribution
to the risk is from the situation that the pilot thinks to be proceeding on a normal
taxiway. The relative size of this contribution depends on the crossing distance and
varies from 64% for crossing at 500 m to about 83% for crossing at 1000 or 2000 m.
A more complete overview of the contributions to the collision risk is provided by a
projected version of the collision risk tree in Figure 8. It shows the contributions of
events related to the situation awareness of the pilot of the taxiing aircraft (Cross
runway/Proceed runway) and the functioning of ATC alert and communication
systems (Up/Down). The collision risk results in the leaves of the tree are the product
of the probability of the event combination indicated and the Monte Carlo simulation
based collision risk given the event combination. The results in Figure 8 show that
the risk is dominated by situations with a pilot flying of a taxiing aircraft having an
erroneous situation awareness and the ATC alert and communication systems
working nominally.