§ 121.584 – Requirement to view the area outside the flightdeck door.
From the time the airplane moves in order to initiate a flight segment through the end of that flight segment, no person may unlock or open the flightdeck door unless:
(a) A person authorized to be on the flightdeck uses an approved audio procedure and an approved visual device to verify that:
(1) The area outside the flightdeck door is secure, and;
(2) If someone outside the flightdeck is seeking to have the flightdeck door opened, that person is not under duress, and;
(b) After the requirements of paragraph (a) of this section have been satisfactorily accomplished, the crewmember in charge on the flightdeck authorizes the door to be unlocked and open.