Section 91.105 - Flight crewmembers at stations(a) During takeoff and landing, and while en route, each required flight crewmember shall- (1) Be at the crewmember station unless the absence is necessary to perform duties in connection with the operation of the aircraft or in connection with physiological needs; and(2) Keep the safety belt fastened while at the crewmember station.(b) Each required flight crewmember of a U.S.-registered civil aircraft shall, during takeoff and landing, keep his or her shoulder harness fastened while at his or her assigned duty station. This paragraph does not apply if-(1) The seat at the crewmember's station is not equipped with a shoulder harness; or(2) The crewmember would be unable to perform required duties with the shoulder harness fastened.Doc. No. 18334, 54 FR 34294, Aug. 18, 1989, as amended by Amdt. 91-231, 57 FR 42671, Sept. 15, 1992