The second-in-command's (SIC) engagement of the emergency parking brake (EPB), which decreased the airplane's braking performance and prevented it from stopping on the available runway. Contributing to the SIC's decision to engage the EPB was the lower-than-anticipated deceleration due to a wet-runway friction level that was far lower than the levels used to determine the wet-runway stopping distances in the Airplane Flight Manual (AFM) and necessitated a landing distance considerably greater than that published in the AFM.