  The Pierre Auger Observatory is designed to elucidate the origin and nature
of Ultra High Energy Cosmic Rays using a hybrid detection technique. A first
run of data taking with a prototype version of both detectors (the so called
Engineering Array) took place in 2001-2002, allowing the Collaboration to
evaluate the performance of the two detector systems and to approach an
analysis strategy. In this contribution, after a brief description of the
system, we will report some results on the behavior of the Fluorescence
Detector (FD) Prototype. Performance studies, such as measurements of noise,
sensitivity and duty cycle, will be presented. We will illustrate a preliminary
analysis of selected air showers. This analysis is performed using exclusively
the information from the FD, and includes reconstruction of the shower geometry
and of the longitudinal profile
