FIRE EXTINGUISHING UTILITY SYSTEMS

nozzle located at the base of each windshield. A timer circuit regulates the sequence of flow. The rain repellent fluid is distributed over the wind- shield surface by the windshield wipers and free stream air. A transparent film is formed that greatly reduces water adhesion. The film causes the water to form into streams, thereby preventing production of a vision-distorting film. The rain repellent system is actuated by setting the wiper switch on the windshield panel to HIGH (fig. 1-22). This is done to minimize the possibility of rain repellent fluid discharge on a near-dry windshield, which could impair vis- ibility. When the rain repel switch is depressed, both valve nozzle assemblies open, and the timer is energized. Rain repellent fluid flows from the nitrogen-pressurized container, through the manifold and plumbing, and out through the two valve/nozzle assembly solenoid shut- off valves onto the windshields. The valve nozzle assemblies are energized by 28-Vdc power from the left primary dc bus. The rain repel switch must be released and again depressed for additional applications of rain repellent fluid. Approximately 60 applications are available from a full container. The rain repellant system consists of a recharge- able container and manifold, valve/nozzle assembly, and plumbing. RECHARGEABLE CONTAINER AND MANIFOLD Rain repellent fluid is stored in a nitrogen- pressurized rechargeable container located be- hind the pilot’s seat. Container capacity is approximately 0.9 pint. Container pressure varies from 75 psi (full) to approximately 30 psi (nearly empty). A manifold is mounted on the container. The manifold incorporates a pressure gage that indicates pressure in the container. VALVE/NOZZLE ASSEMBLY Two valve/nozzle assembly solenoid shutoff valves, one for each windshield, are located at the base of the windshields. An adjustable timer circuit governs the amount of fluid released onto the windshields. PLUMBING Plumbing consists of tube assemblies that connect the container to the valve/nozzle assemblies. A drain cap is located at the low point of the plumbing. FIRE EXTINGUISHING UTILITY SYSTEMS Learning Objective: Identify operating principles, components, and maintenance procedures for fire extinguishing utility systems. As a general rule, fire extinguishing systems are incorporated only in multiengined aircraft. These systems are designed primarily for extinguishing engine fires; however, on some aircraft, provision is made for protecting the aircraft heater (or heaters), as well as the engines. The extinguishing agent is stored in cylinders mounted at various places within the fuselage, wings, nacelles, or landing gear wells, and is directed to the area of fire through a system of tubing and various control valves. A switch or pull’ handle, located at the pilot’s or flight engineer’s station, is used in releasing the extinguishing agent when a fire occurs. The inspection and maintenance of aircraft fire extinguishing systems is an important responsibility of the AME. TRIFLUOROBROMOMETHANE (CF3Br) CF3Br (the chemical symbol for trifluoro- bromomethane) is a fluorinated hydrocarbon. It is the most common extinguishing agent used in aircraft fire extinguishing systems. It is a more efficient extinguishing agent than CO2, and under normal atmospheric pressure and temperature, it is a colorless, odorless, and tasteless gas. It exists as a liquid only when contained under pressure. CF3Br is nontoxic, noncorrosive, leaves no residue, does not deteriorate with age, is an electrical insulator, and goes farther than CO2. NOTE: CF3Br is very volatile. It is nontoxic but a danger of suffocation exists because, like carbon dioxide, CF3Br replaces oxygen when breathed. Among the many fire extinguishing 1-30