There are several different types of fire detections systems used to detect engine fires on aircraft. Two of the most common types used are spot detectors and continuous loop systems. Spot detector systems use individual sensors to monitor places in which fire could occur. Some examples include the thermal switch system, the thermocouple system, the optical fire detection system, and the pneumatic-based thermal fire detection system. By contrast, continuous loop systems provide more completed fire detection coverage by using several loop-type sensors. As such, they are more often used on transport-type aircraft that require greater supervision.
Thermal Switch System
Thermal switch systems are a type of fire detection system which is often found in older-model aircraft. They include one or more lights that are energized by the aircraft power system and several thermal switches that control operation of the light(s). When the thermal switches reach a certain temperature, they complete a circuit, alerting the pilot and crew. They are usually connected parallel to each other but in a series with the indicator lights so that if any one section of the circuit is shut, it will complete the light circuit to indicate a fire or overheat condition.
Rather than responding to a certain temperature, thermocouple systems will send an alert dependent on the rate of temperature rise. As such, they will not give a warning when an engine slowly overheats or a short circuit develops. The system consists of a relay box, warning lights, and thermocouples. The wiring systems of these units may be divided into the following circuits: the detector circuit, the alarm circuit, and the test circuit.
Optical Fire Detection Systems
Optical fire detection systems are designed to alarm when they detect the presence of prominent, special radiation emissions from hydrocarbon flames. There are two major types which are infrared (IR) and ultraviolet, that are based on the specific emission wavelengths they are designed to detect. IR-based optical flame detectors are often used on light turboprop aircraft and helicopter engines. These sensors have proven to be very dependable and economical for simple applications.
Pneumatic Thermal Fire Detection
Pneumatic detectors consist of a helium-filled tube connected at one end to a responder assembly. As the element is heated, the gas pressure inside the tube increases until the alarm threshold is reached. Then, an internal switch closes and sends an alarm to the cockpit. The pneumatic detector integrity pressure switch opens and triggers the fault alarm if the pneumatic detector loses pressure, as in the case of a leak.
Continuous-Loop Detector Systems
Large commercial aircraft usually use continuous thermal sensing elements for their protection because these systems offer superior detection performance and coverage, and they can resist harsh environments. A continuous loop detector provides more complete coverage of a fire hazard area than any of the spot-type temperature detectors. However, they rely on similar technology, and are versions of the thermal switch system. Consequently, they are heat-sensitive systems that will complete a circuit at a certain temperature. The two most widely used types of continuous-loop systems are the Kidde and the Fenwal systems.
There are many types of fire detection systems installed on aircraft to detect dangerous engine malfunctions. While some of them rely on independent sensors, such as in spot detectors, others take advantage of a looping system of indicators for more complete coverage. For access to dependable aircraft devices such as fire detection systems, we at Emergent Purchasing invite you to browse our online catalog of items. Prioritizing quality and authenticity at every step of the way, we subject countless items to strict quality testing and high standards fit for their use in aircraft. Explore our vast inventory and start the purchasing process today to experience a procurement process that is uniquely convenient and fit for your needs.
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