We are interested in jobs scheduling in flexible manufacturing systems. We try to combine predictive methods which guarantee optimal or good results but are not very robust to perturbations and reactive methods which take into account the real state of the system. For this, we use a method called the group sequencing method which aims at characterizing a set of solutions for the scheduling problem, instead of a single one. This method enables to add sequential flexibility to the operations to process. At the same time, this method guarantees a minimal quality in regards with the performance objectives. In this paper, we are interested in the behavior of this method in regards with both predictive and reactive methods, especially with various degrees of uncertainties. We present the experiments conducted on a real flexible manufacturing system to compare the performances of three scheduling methods in regards with uncertainties on the transportation times: the group sequencing approach, a predictive one and a reactive one. The results show very good performance with the group sequencing method.