**1. Introduction**

The BS distribution was originally introduced in [1] to model the fatigue in the lifetime of certain materials. During the last decades, mainly due to its good properties, the use of this model spread out to other fields, such as economics and environmental sciences. In these applied scenarios, quite often, departures of the BS model are found, and therefore it is necessary to introduce some improvements. In this paper, we focus on those situations in which extra asymmetry or bimodality are present in our data, and a generalization of the BS model should be considered to deal with these issues. To reach this end, a flexible BS model is introduced. Our proposal is based on the flexible skew-normal distribution introduced in [2], and includes, as particular cases, the BS and skew BS distribution. Next, we briefly describe the key aspects that properly combined result in the flexible BS model. These are asymmetry, bimodality and main features of the basic BS model.
