Duties of operators to prevent excessive fatigue of flight crew

It shall be the duty of every operator of an aircraft to which this Article applies to ensure, as respects each person flying as a member of the flight crew of that aircraft, that the periods during which that person is required or permitted by that operator to carry out any work or other duties are so limited in length and frequency, and that that person is afforded such periods for rest, that his said work and duties are not likely to cause him such fatigue while he is flying in the aircraft as may endanger the safety thereof.