Aircraft Oxygen Equipment — Page 275, Lesson 353

Let’s start with the regulatory backbone of aircraft oxygen. This is Appendix 1 to OPS 1.770, which sets the minimum oxygen supply requirements for pressurised aeroplanes during and after an emergency descent. I want you to think of this as a legal table that tells you exactly how much oxygen you must carry for each category of person on board, and for how long, based on cabin pressure altitude. First, the key concept: cabin pressure altitude. That’s the altitude in the standard atmosphere that corresponds to the actual pressure inside the cabin. Even in a pressurised aeroplane, if the pressurisation fails or you’re flying high, the cabin altitude can rise to a level where you need supplemental oxygen. The table gives you thresholds in feet. Now, let’s walk through the five supply categories. Category 1: all occupants of flight deck seats on flight deck duty. That’s the pilots. They need oxygen for the entire flight time when cabin pressure altitude exceeds 13,000 feet, and also for the entire flight time when cabin pressure altitude exceeds 10,000 feet but does not exceed 13,000 feet, but only after the first 30 minutes at those altitudes. So there’s a 30-minute grace period at the lower band. However, the supply must never be less than 30 minutes for aeroplanes certificated to fly at altitudes not exceeding 25,000 feet, and never less than two hours for aeroplanes certificated to fly at altitudes more than 25,000 feet. Note 2 and Note 3 define what those minimums mean, and I’ll get to them. Category 2: all required cabin crew members. They need oxygen for the entire flight time when cabin pressure altitude exceeds 13,000 feet, but not less than 30 minutes, and for the entire flight time when cabin pressure altitude is greater than 10,000 feet but does not exceed 13,000 feet after the first 30 minutes at those altitudes. So cabin crew get the same 10,000-to-13,000-foot band with the 30-minute grace, but their floor at the higher band is 30 minutes. Category 3: 100% of passengers. They need oxygen for the entire flight time when cabin pressure altitude exceeds 15,000 feet, but in no case less than 10 minutes. Note 4 defines that minimum. Category 4: 30% of passengers. They need oxygen for the entire flight time when cabin pressure altitude exceeds 14,000 feet but does not exceed 15,000 feet. Category 5: 10% of passengers. They need oxygen for the entire flight time when cabin pressure altitude exceeds 10,000 feet but does not exceed 14,000 feet, after the first 30 minutes at those altitudes. Now, Note 5 is important: for the purpose of this table, “passengers” means passengers actually carried and includes infants. So infants count as passengers for these calculations. Let me now explain the notes that define the minimum supply quantities. Note 1 says the supply provided must take account of the cabin pressure altitude and descent profile for the routes concerned. So you can’t just use a generic number; you have to consider the actual route and how the cabin altitude behaves. Note 2 defines the minimum supply for the 30-minute case. It’s the quantity of oxygen necessary for a constant rate of descent from the aeroplane’s maximum certificated operating altitude to 10,000 feet in 10 minutes, followed by 20 minutes at 10,000 feet. So that’s a 10-minute descent plus 20 minutes at the lower altitude, totalling 30 minutes. Note 3 defines the two-hour minimum. It’s the quantity of oxygen necessary for a constant rate of descent from the aeroplane’s maximum certificated operating altitude to 10,000 feet in 10 minutes, followed by 110 minutes at 10,000 feet. That’s 10 plus 110, totalling 120 minutes, or two hours. Note 3 also says the oxygen required in OPS 1.780 (a)1 may be included in determining the supply required. So you can count that other required oxygen toward this total. Note 4 defines the 10-minute minimum for 100% of passengers. It’s the quantity of oxygen necessary for a constant rate of descent from the aeroplane’s maximum certificated operating altitude to 15,000 feet in 10 minutes. So that’s a straight 10-minute descent to 15,000 feet. Let me tie this together. The table gives you the duration and cabin pressure altitude conditions for each category. The notes give you the physical meaning of the minimum quantities. For the pilots, the 30-minute or two-hour floor is defined by a specific descent profile. For passengers at 100%, the 10-minute floor is a descent to 15,000 feet. For cabin crew, the 30-minute floor is the same as Note 2. One thing to notice: the thresholds are cumulative in a sense. At 10,000 to 14,000 feet, you need 10% of passengers. At 14,000 to 15,000 feet, you need 30%. Above 15,000 feet, you need 100%. And the pilots and cabin crew have their own bands. This is a regulatory table, so you must memorise the exact numbers and the exact conditions. In an exam or in real operations, you’ll be asked to determine the required oxygen supply for a given flight profile. Now, let me also mention the figure that illustrates this. shows the oxygen flow profile for a chemical oxygen generator. That’s a different piece of equipment, but it relates to how the oxygen is actually delivered once you’ve determined the supply requirement. And shows crew portable oxygen, which is the equipment the crew would use. But for now, focus on the table and the notes, because that’s the regulatory foundation. Let me recap the critical numbers so they stick. Pilots: 30 minutes minimum for aircraft certificated up to 25,000 feet, two hours for aircraft certificated above 25,000 feet. Cabin crew: 30 minutes minimum. Passengers: 100% for above 15,000 feet with a 10-minute floor, 30% for 14,000 to 15,000 feet, 10% for 10,000 to 14,000 feet after 30 minutes. And the minimum quantities are defined by specific descent profiles: 10 minutes to 10,000 feet plus 20 minutes there for the 30-minute case, 10 minutes to 10,000 feet plus 110 minutes there for the two-hour case, and 10 minutes to 15,000 feet for the 10-minute case. That’s the core of Appendix 1 to OPS 1.770. You now have the regulatory minimums for supplemental oxygen in pressurised aeroplanes during and after an emergency descent.