  The Stratospheric Observatory for Infrared Astronomy (SOFIA) has recently
concluded a set of engineering flights for Observatory performance evaluation.
These in-flight opportunities are viewed as a first comprehensive assessment of
the Observatory's performance and are used to guide future development
activities, as well as to identify additional Observatory upgrades. Pointing
stability was evaluated, including the image motion due to rigid-body and
flexible-body telescope modes as well as possible aero-optical image motion. We
report on recent improvements in pointing stability by using an active mass
damper system installed on the telescope. Measurements and characterization of
the shear layer and cavity seeing, as well as image quality evaluation as a
function of wavelength have also been performed. Additional tests targeted
basic Observatory capabilities and requirements, including pointing accuracy,
chopper evaluation and imager sensitivity. This paper reports on the data
collected during these flights and presents current SOFIA Observatory
performance and characterization.
