The en route controller is generally responsible for monitoring
an assigned frequency using a single radar display. However,
at night, it is not uncommon for sectors to be amalgamated,
resulting in the controller having to monitor more than one frequency. The division of auditory attention across multiple
frequencies does not result in any performance costs that
warrant concern given the low traffic load observed at night.
On the night of the accident, the controller was monitoring
two radio frequencies, the first used by en route aircraft and
the second for aircraft on approach to the Friedrichshafen
airport (FHA) in Germany. There are two important issues to
note here. Firstly, arrival traffic at that airport at night was
extremely rare. Secondly, the controller chose to have the
radar information for traffic approaching the airport displayed
on a separate monitor. As a result, the controller had to
monitor two display consoles that were separated by over a
meter, resulting in the maintenance of divided attention for a
sustained period of time. As fate would have it, there were two
aircraft on approach that night to the airport. The controller
had earlier coordinated the approach for the first aircraft to
land on runway 06. Following this, the second aircraft on
approach requested runway 24 at FHA. In order to provide this
clearance, the en route controller first had to obtain permission
from the airport tower. To do so, he had to use the automated
phone system