Section 125.315 - Admission to flight deck(a) No person may admit any person to the flight deck of an airplane unless the person being admitted is-(2) An FAA inspector or an authorized representative of the National Transportation Safety Board who is performing official duties; or(3) Any person who has the permission of the pilot in command.(b) No person may admit any person to the flight deck unless there is a seat available for the use of that person in the passenger compartment, except-(1) An FAA inspector or an authorized representative of the Administrator or National Transportation Safety Board who is checking or observing flight operations; or(2) A certificated airman employed by the certificate holder whose duties require an airman certificate.