A connection assembly of an engine pylon underneath an aircraft wing, the wing being provided with a fitting, the engine pylon being provided with a fork joint nested in the fitting and fixed to the said fitting by means of a traversing pin system, including: an external primary pin, a secondary pin mounted inside the primary pin, a primary shoulder mounted directly around the primary pin, at a blind end of the pin system, to block the said pin in translation, a secondary shoulder mounted around one end of the secondary pin, at a blind end of the pin system, to block the system in rotation, and an interlocking assembly mounted around the primary pin and the secondary pin, at a free end of the pin system, to block the pin system in translation.