9. An employer shall ensure that in any month—
(a)no person employed by him shall act as a crew member during the course of his working time, if during the period of 12 months expiring at the end of the month before the month in question the aggregate block flying time of that person exceeds 900 hours; and
(b)no crew member employed by him shall have a total annual working time of more than 2,000 hours during the period of 12 months expiring at the end of the month before the month in question.