Citation Excel (C560XL)
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft; Human Factors
While talking with [the copilot]; he noticed that a blade on the left engine was damaged. About two inches was missing from the tip of a blade.  During preflight that evening; it was raining heavily and I was wearing a rain jacket with a hood and aircraft was given a fast preflight. I didn't notice anything amiss. During the night's flight; the aircraft never had any incidents whatsoever. The aircraft had to be damaged by something while sitting on the ramp; because only one blade was damaged.
Citation 560XL Captain reported noticing fan blade damage while conducting the exterior preflight inspection; with no previous record of the occurrence.