This paper presents a step wise formal development oft helanding system of an aircraft. The formal models include the complex behaviour, temporal behaviour and sequence of operations of the landing gear system. The models are formalized in Event-B modeling language, and then the ProB model checker is used to verify the deadlock freedom and to validate the behaviour requirements by animating the formalized models. This case study is considered as a benchmark for techniques and tools dedicated to the verification of behavioural properties of the complex critical systems.