Aircraft Oxygen Equipment — Page 261, Lesson 339

Right, let's get into the oxygen equipment. This is a brand-new chapter for us, and it's a critical one for your operations. We're starting with the fundamental question: why do pressurized aircraft even need a dedicated oxygen system? It's not just for comfort. The rules are very specific. The crew must be provided with oxygen if the cabin pressure altitude exceeds 13,000 feet. There's also a time-based rule: if the aircraft is at a cabin pressure altitude between 10,000 and 13,000 feet for more than 30 minutes, the crew needs oxygen. And there's a safety rule: if hazardous fumes enter the flight deck, the crew gets oxygen. Now, for the passengers, the requirements are tiered based on cabin altitude. If the cabin pressure altitude exceeds 15,000 feet, all passengers must be provided with oxygen. If it's above 14,000 feet, 30% of the passengers need it. And if it's above 10,000 feet, 10% of passengers need it. These aren't just suggestions—they're regulatory requirements, and I want you to note the reference: JAR-OPS 1 Subpart K, specifically appendix 1 to JAR-OPS 1.770 and appendix 1 to JAR-OPS 1.775. That's your source document for these rules. Beyond the fixed systems, there are portable oxygen sets. These are provided for therapeutic use by passengers—so if a passenger has a medical condition—and for use by cabin staff during emergencies. There's also the possibility of special smoke sets for crew use, which are exactly what they sound like: protective breathing equipment. Now, what about unpressurized aircraft? If an unpressurized aircraft is going to fly above 10,000 feet, it must have oxygen equipment installed for both passengers and crew. And if there's no fixed installation, then portable oxygen sets must be provided instead. Let's talk about how the oxygen is stored. Crew oxygen is stored in High Pressure gaseous form. Passenger supplies can be either High Pressure gas or chemically generated. The gaseous systems come in two types. For crew, it's generally the diluter demand type. For passengers, it's the continuous flow type. Some smaller aircraft might use the continuous flow type for the crew as well, but the standard is diluter demand for crew. Here's a key detail on the storage. In both systems, the gas is stored in cylinders at 1800 psi. That's a very high pressure, so it has to be reduced to a suitable level for use before it reaches you. Now, let's look at the indications and safety features. There's a quantity, or pressure, indication provided by a gauge on the flight compartment. That's how you monitor your supply. For safety, if there's an overpressure, the cylinder is vented to atmosphere through a safety disc—also called a bursting disc. And here's the clever part: there's a discharge indicator located on the outer skin of the aircraft, right next to the oxygen storage bottle. If that disc bursts, the indicator shows it, so ground crew can tell the bottle has discharged without opening anything up. Finally, the cylinders are fitted with shut-off valves. These allow the cylinders to be removed from the aircraft for maintenance purposes. You isolate the cylinder, then you can take it out safely. So to recap the architecture: high-pressure storage at 1800 psi, pressure reduction for use, a gauge in the flight deck, a bursting disc for overpressure with an external discharge indicator, and shut-off valves for maintenance. That's the foundation. Next, we'll look at the continuous flow system in detail.