The KeY system allows for the integrated informal and formal development of object-oriented Java software. In this paper we report on a major industrial case study involving safety-critical software for the computation of a particular kind of railway timetable used by train conductors. Our case study includes formal specification of requirements both on the analysis and the implementation level. Particular emphasis in our research is placed on the challenge to make authoring and maintenance of formal specifications easier. We demonstrate that the technique of specification patterns as implemented in KeY for the language OCL yields significant improvements.