Oxygen indicators
91.  An operator of a Singapore registered aircraft that is to be operated at any altitude above flight level 130, or for more than 30 minutes at an altitude between flight level 100 up to and including flight level 130, must ensure the aircraft is equipped with a means of indicating to the flight crew —
(a)whether the passenger oxygen system is activated;
(b)if the oxygen system is supplied by a gaseous system, the amount of breathing oxygen available in each source of supply; and
(c)if the aircraft is a pressurised aircraft, by visual or aural warning, when the cabin pressure altitude exceeds 10,000 ft.