Passenger Supplemental Oxygen - Oxygen Systems - Airframes & Aircraft Systems #55

Summary

This lesson explores the supplemental oxygen systems for passengers and cabin crew on airplanes. It discusses the continuous flow type systems, the storage of masks in passenger service units, and the automatic/manual deployment mechanisms. The lesson also covers two types of oxygen supply systems: high-pressure gaseous and chemical generator systems. It details the operation of chemical oxygen generators, their maintenance needs, and safety precautions. The script emphasizes regulations for oxygen mask availability and the oxygen flow process during emergencies.

Takeaways

• 🌐 The lesson discusses the oxygen systems for passengers and cabin crew on airplanes.
• 🔄 The supplemental oxygen supply is of the continuous flow type, ensuring a constant supply regardless of usage.
• ✈️ On some smaller aircraft, the flight deck may also use a continuous flow system for oxygen supply.
• 💨 The oxygen masks are stowed in passenger service units and are automatically deployed when the cabin altitude reaches 14,000 feet or can be manually deployed by the flight crew.
• 🔗 There are two methods for automatic door actuation in the gaseous system: pneumatically by oxygen pressure or electrically by solenoids in systems with chemical generators.
• 📏 Regulations mandate that aircraft operating above 25,000 feet must have 10% more oxygen masks than the number of cabin seats.
• 🛫 Oxygen enters the mask through a rebreather bag, where it mixes with exhaled air and cabin air, but it does not protect against noxious fumes.
• 🔧 A high-pressure gaseous oxygen supply system is similar to the CRU system but uses mass connection points instead of demand regulators.
• 🔬 Chemical oxygen generators are used on most modern aircraft; they are light, inexpensive, and virtually maintenance-free.
• ⏱️ When ignited, the chemical reaction in the generator produces heat and releases oxygen, which is then filtered and regulated to a safe temperature and pressure for breathing.

Q & A

What type of oxygen systems are provided for passengers and cabin crew in an aircraft?

The aircraft provides continuous flow type oxygen systems for passengers and cabin crew.

How does the oxygen supply system differ between high-pressure gaseous systems and chemical generator systems?

In high-pressure gaseous systems, the oxygen masks are stowed in passenger service units that open automatically by a barometric release mechanism, while in chemical generator systems, the masks are also stowed in service units but are opened by electrical solenoids.

What triggers the automatic opening of the oxygen mask doors in the passenger service units?

The doors open automatically if the cabin altitude reaches 14,000 feet or by manual selection by the flight crew at any altitude.

How does the oxygen flow initiate when a passenger pulls the mask towards their face?

Pulling the mask towards the face pulls a cord which either opens a check valve in the gas supply system or operates an electrical or percussion cap firing mechanism on the chemical generator, initiating the oxygen flow.

What is the regulation for the number of oxygen masks required on aircraft intended to be operated above 25,000 feet?

The number of masks must exceed the number of cabin seats available by 10%, with the extra masks spread evenly throughout the cabin.

How does the oxygen enter the mask and what does it mix with before being inhaled by the passenger?

The oxygen enters the mask through a plastic rebreather bag, where it is mixed with exhaled air and cabin air.

Why don't passenger oxygen masks provide protection from noxious fumes?

Passenger oxygen masks don't provide protection from noxious fumes because they mix the oxygen with cabin air, which could contain such fumes.

How does a high-pressure gaseous oxygen supply system differ from a chemical oxygen generator system?

In a high-pressure gaseous oxygen supply system, demand regulators are replaced by mass connection points with valves operated by mass cords, and there is also a flow control valve that can be opened automatically by a barometric switch or manually by a flight deck switch.

What are the main components of a chemical oxygen generator used in aircraft?

A chemical oxygen generator consists of a charge block made of sodium chlorate and iron powder, surrounded by filter material and thermal insulation, all housed in a cylindrical case.

How long does a chemical oxygen generator typically burn and what is its oxygen output?

A chemical oxygen generator burns at a temperature of approximately 200 degrees Celsius for a minimum of 15 minutes, releasing about 45% of its weight as usable oxygen.

How does a relief valve in a chemical oxygen generator system function?

A relief valve prevents the internal pressure in the generator from exceeding 50 psi, ensuring the safety of the system.