Aircraft Oxygen Equipment — Page 275, Lesson 355

I want to walk you through the regulatory side of aircraft oxygen equipment now. This is the part of the syllabus where the rules tell us exactly who gets oxygen, how much, and under what conditions. We're looking at the requirements that follow a cabin pressurisation failure. Let me start with the fundamental assumption that underpins everything. Following a cabin pressurisation failure, the cabin pressure altitude shall be considered the same as the aeroplane pressure altitude. In plain terms, if the pressurisation system fails, we assume the cabin is at the same altitude as the aircraft itself. There is one escape clause: unless it is demonstrated to the Authority that no probable failure of the cabin or pressurisation system will result in a cabin pressure altitude equal to the aeroplane pressure altitude. So if the manufacturer can prove to the regulatory Authority that no realistic failure could ever make the cabin equal the outside altitude, then the demonstrated maximum cabin pressure altitude may be used as the basis for determination of oxygen supply. That's the foundation — the default is worst case, and the demonstrated maximum is the exception. Now we move into the oxygen equipment and supply requirements, and they split the occupants into two groups: flight crew, and then cabin crew, additional crew, and passengers. Let's take flight crew first. Each member of the flight crew on flight deck duty shall be supplied with supplemental oxygen in accordance with Appendix 1. That appendix is the detailed schedule of oxygen quantities and durations — for now, just know it's the governing table. Here's a subtle and important rule: if all occupants of flight deck seats are supplied from the flight crew source of oxygen supply, then they shall be considered as flight crew members on flight deck duty for the purpose of oxygen supply. So the source of supply defines the status. If someone in a flight deck seat is drawing from the flight crew oxygen source, they count as flight crew for oxygen purposes. But if a flight deck seat occupant is not supplied by the flight crew source, they are to be considered as passengers for the purpose of oxygen supply. And the same logic extends further: flight crew members not covered by that first subparagraph — meaning not on flight deck duty and not supplied from the flight crew source — are also to be considered as passengers for oxygen supply purposes. Then we have the physical placement and design requirements. Oxygen masks shall be located so as to be within the immediate reach of flight crew members whilst at their assigned duty station. So the mask has to be right there, reachable without leaving the seat. And for pressurised aeroplanes operating above 25 000 ft, the oxygen masks for use by flight crew members shall be a quick donning type of mask. That's a specific design requirement — above 25 000 feet, the crew can't afford to fumble with a slow mask, so it must be the quick donning type. Now for the second group: cabin crew members, additional crew members, and passengers. Cabin crew members and passengers shall be supplied with supplemental oxygen in accordance with Appendix 1, except when subparagraph (v) applies — and that subparagraph is coming in the next part of the text. There's also a note about cabin crew carried in addition to the minimum number required — and that sentence is cut off here, but we'll pick it up right there. Let me pause and make sure the key contrasts are clear, because this is where exam questions live. The status of a person — flight crew or passenger — is determined by which oxygen source supplies them, not by their job title. Flight deck seat occupants on the crew source are crew. Flight deck seat occupants off the crew source are passengers. Flight crew not on flight deck duty and not on the crew source are passengers. And the altitude threshold of 25 000 ft triggers the quick donning mask requirement for flight crew in pressurised aeroplanes. That's the regulatory framework for oxygen supply