Fire Detection and Protection — Page 310, Lesson 380

I want to walk you through the fire detection and protection systems, starting with the extinguishing agents and the different classes of fire compartments. First, let's talk about sand. Sand is useful for containing metal fires, such as magnesium or titanium. The key point here is that for these specific metals, using liquids would actually make matters worse. So sand is the agent of choice for those particular fires. Now, hand held extinguishers. The regulations specify exactly how many you need based on passenger capacity. Let me give you that scale: 7 to 30 passengers requires 1 extinguisher. 31 to 60 requires 2. 61 to 200 requires 3. 201 to 300 requires 4. 301 to 400 requires 5. 401 to 500 requires 6. 501 to 600 requires 7. And 601 to 700 requires 8. There's an important additional requirement. At least two of the extinguishers in the passenger compartment of an aircraft with a maximum seating configuration of 61 seats or more must be BCF. And there must be at least one additional BCF hand extinguisher conveniently located in the flight deck. So BCF is a specific type of extinguishing agent, and the regulation mandates its presence in those locations. Now let's move to fire systems and compartments. There are three types of systems in general aircraft use. The first is the Fixed System. This consists of containers holding the extinguishing agent that are fixed to the structure, along with a system of distribution pipes and controls. It's provided for the protection of power plants and, where applicable, the auxiliary power units. On large aircraft, fixed systems may also be provided for the protection of landing gear bays and baggage compartments. The second is the Portable System. This refers to the several types of hand operated fire extinguishers provided to combat any outbreak of fire in flight crew compartments or passenger cabins. The third is the Mixed Systems. This is an arrangement used in some aircraft for the protection of baggage and service departments. It consists of a system of distribution pipes and spray rings mounted in the appropriate compartment, complemented by hand held or mounted fire extinguishers discharged through special adapter points. Now, let's look at fire compartments under JAR-25. The cockpit and passenger cabin are designated Class A compartments. This means that a fire may be visually detected, reached, and combatted by a crew member. The engines are Class C compartments, and fire detection and warning is provided. There are five types of cargo compartments, Class A through E. Class A and B are ones where crew members may reach and combat a source of fire. Class C or D are ones where crew members cannot reach the source of fire. A Class E cargo compartment is one on aeroplanes used only for the carriage of cargo. Class A compartments comply with three specific requirements. First, they provide for visual detection of smoke. Second, they are accessible in flight. Third, there is a fire extinguisher available. So the key distinction here is accessibility. Class A and B cargo compartments allow crew to physically reach and fight the fire. Class C and D do not. And Class E is a special case for cargo-only aeroplanes. Let me show you the typical fire warning indicators and the cockpit overhead engine fire panel so you can see how these systems appear in the cockpit. And here's the fire detection loop test, which shows how the detection loops are tested. That covers the extinguishing agents, the three system types, and the compartment classifications. The critical things to remember are the passenger capacity scale for extinguisher counts, the BCF requirements, and the distinction between Class A and B compartments where crew can reach the fire versus Class C and D where they cannot.