  The aim is to show that in case of low probability of asteroid collision with
Earth, the appropriate selection and weighing of the data are crucial for the
impact investigation, and to analyze the impact possibilities using extensive
numerical simulations. By means of the Monte Carlo special method a large
number of ``clone'' orbits have been generated. A full range of orbital
elements in the 6-dimensional parameter space, e.g. in the entire confidence
region allowed by the observational material has been examined. On the basis of
1000 astrometric observations of (99942) Apophis, the best solution for the
geocentric encounter distance of 6.065\pm 0.081 R_{Earth} were derived for the
close encounter with the Earth on April 13, 2029. The present uncertainties
allow for the special configurations (``keyholes'') during these encounter
which may lead to the very close encounters in the future approaches of
Apophis. Two groups of keyholes are connected with the close encounter with the
Earth in 2036 (within the minimal distance of 5.7736-5.7763 R_{Earth} on April
13, 2029) and 2037 (within the minimal distance of 6.3359-6.3488 R_{Earth}).
The nominal orbits for our most accurate models run almost exactly in the
middle between these two impact keyhole groups. A very small keyhole for the
impact in 2076 has been found between these groups at the minimal distance of
5.97347 R_{Earth} (close to the nominal orbit).
