1374A-5

1374A-5 thermal switch in aircraft air ducts

The 1374A-5 is an aircraft thermal switch used in air ducts and air-heating circuits where automatic electrical switching is required at a specified air temperature. The unit reacts to the temperature of the airflow passing through the duct and changes the state of its electrical contacts when the set threshold is reached. In aircraft systems, this type of device is used as a simple and reliable temperature-controlled element for automation circuits. It does not measure temperature for display purposes; its purpose is to provide a switching command to connected control relays, contactors, or monitoring circuits.

1374A-5 in Mi-8 and Mi-17 heating systems

On Mi-8 and Mi-17 family helicopters, the 1374A-5 can be used as part of the heating and ventilation equipment, including systems associated with kerosene-fired air heaters such as KO-50. In this application, the thermal switch monitors the temperature condition inside the air path and provides a control signal when the air temperature reaches or falls through the required operating point. This makes the unit relevant for heater control logic, fan control, and safe operation of air-heating equipment during start-up, normal operation, and shutdown sequences.

KO-50 fan control function of the 1374A-5

In heater-related circuits, the 1374A-5 may be used to support automatic fan operation. The switch can provide a signal for disconnecting or controlling the fan unit when the outlet air temperature from the heater drops below the required threshold. This prevents unnecessary operation of downstream equipment when the heater is no longer supplying air at the needed temperature. In practical aircraft maintenance, the part should be checked not only by designation, but also by installation position, wiring diagram, heater configuration, and the operating logic described in the aircraft technical documentation.

1374A-5 operating principle and contact switching

The 1374A-5 operates as a temperature-sensitive switching device. Its action is based on the physical response of the sensing element to changes in air temperature. As the temperature changes, the internal mechanism acts on the contact group and closes or opens the electrical circuit. This type of design is suitable for aircraft automation because it provides direct switching without a complex electronic measuring channel. The unit works in low-current DC control circuits and is intended for use with onboard equipment that receives a discrete signal rather than a proportional temperature output.

Aircraft operating conditions for the 1374A-5

The 1374A-5 is made for operation in demanding aircraft conditions, including vibration, airflow, changing duct temperature, and low ambient temperatures. According to the passport data, the unit is designed for use in air ducts with a controlled rate of air temperature change and a specified blowing speed. These parameters are important because the response of a thermal switch depends not only on the nominal actuation temperature, but also on the real airflow conditions around the sensing element. Correct installation in the duct is therefore essential for stable and repeatable operation.

Identification, supply, and documentation of 1374A-5

The 1374A-5 is supplied as an aviation technical item with passport documentation. The passport identifies the product designation, serial number, technical data, resource, storage conditions, and acceptance information. For supply or replacement, the product should be matched with the aircraft parts catalog, maintenance manual, and system documentation for the specific aircraft or heater installation. Depending on stock condition, the unit may be supplied as new production or from storage, with the required passport, label, or quality documentation for aviation use.

Product Type: Aircraft thermal switch
Function: Automatic closing / opening of an electrical control circuit at a specified air temperature
Application / Where Used: Aircraft heating, ventilation, anti-icing, and control automation systems
System / Installation Area: Air ducts and air-heating circuits
Typical Associated Equipment: KO-50 kerosene-fired aircraft heater; fan unit 2438 depending on system configuration
Compatible Aircraft / Equipment: Mi-8 and Mi-17 family helicopters, depending on installed heating system configuration
Operating Principle: Temperature-sensitive mechanical switching element
Actuation Temperature: +15 to +20 °C according to passport data
DC Operating Voltage: 27 ± 2.7 V
Contact Current Load: Not more than 0.5 A
Air Temperature Change Rate in Duct: 16 ± 0.3 °C/min
Air Blowing Speed: 9–12 m/s
Medium Temperature in Duct: −60 to +200 °C
Ambient Air Temperature: −60 to +60 °C
Service Life Before Retirement: 1,500 flight hours within 8 years
Storage Life in Manufacturer Packaging: 3 years
Material Content / Precious Metals: Silver 1.13 g; PdI-10 alloy 0.365 g
Completeness of Supply: Not provided as a set
Weight: 0.277 kg
Technical Documentation: Product passport 1374A-5 PS and manufacturer documentation

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