  The aperture of the Fluorescence Detector (FD) of the Pierre Auger
Observatory is evaluated from simulated events using different detector
configurations: mono, stereo, 3-FD and 4-FD. The trigger efficiency has been
modeled using shower profiles with ground impacts in the field of view of a
single telescope and studying the trigger response (at the different levels) by
that telescope and by its neighbours. In addition, analysis cuts imposed by
event reconstruction have been applied. The hybrid aperture is then derived for
the Auger final extension. Taking into account the actual Surface Detector (SD)
array configuration and its trigger response, the aperture is also calculated
for a typical configuration of the present phase.
