What caused the boat wreck?

Just before sunset, way out in the Mediterranean another migrant boat sank. Some reports say the people on board were trying to attract the attention of an aircraft flying overhead. They had crowded to one side of the boat and it capsized. The Italian navy had several vessels in the are-a. They managed to get their helicopters to the scene quickly as did Maltese forces. They began hauling people out of the water. Many were saved, many were not.