The invention relates to a door (8) designed to be inserted between a cockpit and a cabin of an aircraft, the door comprising a cockpit side (8a) and a cabin side (8b). According to the invention, the door comprises at least one trapdoor (22) capable of closing off a passageway (20) passing through the door and secondly being opened towards the cabin side, the door also comprising a locking/unlocking mechanism (30) of the trapdoor arranged on the cockpit side and that can automatically unlock the trapdoor when the difference between a cockpit pressure and a cabin pressure corresponding to the air pressures applied on the cockpit side and the cabin side of the door respectively is greater than a predetermined value.