About 20:45 the pilot contacted Hamburg Tower for a landing on runway 15. The airplane did not touch down on the runway but the pilot initiated a go-around. With the next radio contact ten minutes later, the pilot reported to the TWR controller that his CitationJet had landing gear problems. During an arranged fly-by of the airplane by the tower, the controller confirmed that the undercarriage was down. Nevertheless the instruments did not show three greens. About 21:20, the aircraft touched down normally with the right-hand landing gear yielding immediately. By counteracting the airplane movement, the pilot managed in delaying ground contact of the right-hand wing and afterwards holding the CitationJet over a distance of 1000 m on the runway. Finally the airplane stopped 30 m to the right beside runway 15 and appr. 300 m in front of the intersection with runway 23. CONCLUSIONS: “The cause of the accident was that: a) the hydraulic system failed as a result of a defective valve; b) the pilot did not accomplish the procedure recommended by the manufacturer in case the landing gear is not positively locked. A contributing factor to b) was that the instruction given by the manufacturer is not clearly formulated.”