The operator's Director of Operations (DO) reported that the flight was dispatched from their home base (first) airport under their Federal Aviation Administration's air carrier operating certificate (14 Code of Federal Regulations, Part 135). A passenger was on board the airplane. Upon arriving at the second airport, the passenger disembarked. The pilot departed without passengers or cargo for the third (accident) airstrip, with the intent of picking up a waiting passenger. Upon arriving over the airstrip, the pilot made a traffic pattern approach and observed that the wind was calm. The pilot stated that his airspeed and approach path were approximately normal, and he was familiar with the airstrip, having landed there in a southerly direction on previous days. The airplane touched down near the beginning of the short, 1,350-foot-long grass runway. The pilot further reported that he used light to firm brake pressure, and the airplane began sliding. He stated that the south portion of the runway (near its departure end) was soggy, and there was a drop-off adjacent to the runway's end. So, to avoid that peril, he attempted a rapid left turn to avoid encountering the drop-off. As the airplane turned left, the right wing dipped down, impacted the ground, and broke. Both the pilot and the DO acknowledged to the National Transportation Safety Board investigator that no runway condition information was ascertained prior to departure for the uncharted, uncontrolled, private airstrip. The DO further reported that flight to the accident airstrip required "special permission," which he granted, having operational control of the airplane. The operator's "General Operations Manual" states that, during the preparation for a flight, it is the pilot-in-command's responsibility to comply with 14 CFR Part 91.103, "Preflight Action." This regulation states that the pilot "...shall, before beginning a flight, become familiar with all available information concerning that flight." The Cessna Aircraft Company's "Landing Distance Table" provides guidelines for ascertaining the approximate landing distance needed under various conditions. Following the accident, the pilot calculated and provided the Safety Board investigator with table data that indicated on a dry grass runway, a distance of at least 897 feet are needed to stop the airplane. The table data does not provide distance information for a "soggy" wet grass runway.