2416-4

2416-4 thermal switch in KO-50 heater automation

The 2416-4 is an aircraft thermal switch used in the control system of the KO-50 kerosene-fired heater installed on Mi-8, Mi-17, Mi-171, and related helicopter platforms. The unit monitors the temperature of heated air at the heater outlet and provides automatic switching of the electrical circuit when the specified temperature level is reached. In the KO-50 system, this thermal switch is used as a discrete control element, not as an indicating temperature sensor. Its task is to issue a clear electrical command to the heater control circuit at the required moment during heater operation.

Ignition control function of the 2416-4 switch

The main function of the 2416-4 in the KO-50 heater is automatic disconnection of the ignition plug circuit. During heater start-up, the ignition plug is required to initiate combustion in the heater chamber. After the air temperature at the heater outlet reaches the set value, combustion is considered stable enough for the ignition plug to be disconnected. At this point, the 2416-4 opens the circuit and removes power from the ignition plug. This reduces unnecessary operation of the ignition element and supports the normal start-up sequence of the heater.

2416-4 in Mi-8 and Mi-17 heating systems

On Mi-8 and Mi-17 family helicopters, the KO-50 heater is used as part of the onboard heating and ventilation system. The 2416-4 thermal switch is installed in the heated-air path and works directly with the thermal condition of the airflow leaving the heater. Its correct operation affects the logic of the heater start cycle, because the ignition plug must remain active long enough to stabilize combustion, but should not stay energized after the heater has reached the required operating condition. This makes the 2416-4 a small but important element in the heater automation chain.

Contact switching principle of 2416-4

The 2416-4 is a contact-type thermal switch with normally closed contacts that open when the sensing element reaches the specified temperature. The device works in aircraft DC control circuits and provides simple on/off switching rather than a proportional temperature signal. Its operating principle is based on thermal expansion of internal elements, which mechanically act on the contact group. This design is suitable for aviation equipment because it provides a direct response to air temperature without a complex electronic measuring channel. The exact circuit connection depends on the KO-50 version and helicopter wiring diagram.

Construction features of the 2416-4 thermal switch

The 2416-4 is similar in construction to other temperature switches used in the KO-50 heater, including 2416-17.5 and 1374A-5, but it has a different actuation setting and a different function in the control sequence. The sensing section is installed in the heated airflow and reacts to temperature changes at the heater outlet. The design is described as a dilatometric thermal switching device, where the difference in expansion of internal materials causes mechanical movement of the contact mechanism. The sensing tube and body are associated with heat-resistant EI946 alloy in technical descriptions of this type of equipment.

System interaction of 2416-4 with related KO-50 components

The 2416-4 works in the same heater automation system as the 2416-17.5 and 1374A-5 thermal devices. Each unit has a separate role. The 2416-4 is connected with ignition plug shut-off after heater start-up. The 1374A-5 is associated with fan control logic, depending on system configuration. The 2416-17.5 provides overtemperature protection and fuel shut-off when the heater outlet temperature exceeds the safe limit. Because these components may look similar, replacement must be made strictly by designation, actuation temperature, installation position, and the aircraft maintenance documentation.

Identification, inspection, and supply of 2416-4

The 2416-4 belongs to aircraft technical equipment and is supplied with passport, label, or quality documentation depending on condition and source. It may be supplied as new production or as a storage item with appropriate acceptance status. During aircraft maintenance, the switch is inspected for secure installation, correct mounting in the air duct, condition of the housing, absence of visible damage, connector condition, and proper routing of the connected wiring harness. For procurement, it is important to specify the exact designation 2416-4, since similar KO-50 thermal switches have different operating temperatures and cannot be treated as interchangeable without documentation approval.

Product Type: Aircraft thermal switch / temperature relay
Designation: 2416-4
Function: Automatic opening of the ignition plug circuit after the heater outlet air reaches the set temperature
Application / Where Used: Aircraft heating and ventilation systems
System / Installation Area: KO-50 kerosene-fired aircraft heater, heated-air outlet duct
Primary System Function: Disconnection of the ignition plug after stable heater combustion is achieved
Compatible Aircraft / Equipment: Mi-8, Mi-17, Mi-171, and related helicopter modifications depending on KO-50 heater installation
Associated Heater: KO-50 kerosene-fired heater
Typical Controlled Component: Ignition plug / starting plug circuit
Associated Ignition Unit / Plug: KV-112 ignition plug, depending on system configuration
Related Thermal Devices: 2416-17.5 thermal switch, 1374A-5 thermal switch
Nominal Actuation Temperature: +40 °C
Permissible Actuation Tolerance: ±10 °C
Possible Adjustment / Operating Range: Approximately +30 to +70 °C depending on production series and technical documentation
Contact Type: Normally closed contacts, opening on heating
Current Type: Direct current
Operating Voltage: 27 V DC aircraft electrical system
Switching Function: Opening / closing of low-current aircraft control circuits
Sensor Type: Dilatometric contact-type thermal switch
Sensing Element Material: Heat-resistant EI946 alloy, according to technical description data
Body Material: EI946 alloy, according to technical description data
Internal Mechanism: Plate springs with contact group
Connection Type: Aircraft-type sealed plug connector, depending on execution
Working Medium: Heated air at the outlet of the KO-50 heater combustion chamber / calorifier
Installation Type: Insert-mounted in the heater duct or housing, with sensing part exposed to airflow
Inspection During Maintenance: Mounting security, housing condition, connector condition, wire harness routing, and absence of visible damage
Supply Category: Aircraft technical item; new production or storage item depending on availability
Technical Documentation: Product passport, quality label, KO-50 heater documentation, and aircraft maintenance documentation as applicable

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