In a flexible collaborative task sharing framework, it is necessary to take situation awareness issues into account. A robot must be able to "understand" the context of the collaboration, especially the difficulty of the task, the willingness of the human to collaborate or his availability. We propose to implement a robotic decision process based on the situation awareness model defined by Endsley. An experiment has been carried out to illustrate an adaptive collaboration in which the robot takes the initiative and fulfill the task that was assigned to the human.