IN-4 zero indicator is an instrument used in the automatic flight control systems of Mi-8/Mi-17 series helicopters, including variants such as Mi-8T, Mi-8MT, Mi-8AMT and Mi-17. The device provides visual indication of control signal deviations within the aircraft’s autopilot channels and assists the crew in monitoring aircraft stabilization.

The indicator responds to input current changes, showing the deviation of the pointer from its neutral reference position. IN-4 enables tracking of the integrity and performance of autopilot control circuits, including sensors, amplification blocks and executive elements.

The indicator is powered from the aircraft’s 27-V DC supply bus. The unit is designed for sustained operation under airborne vibration, temperature gradients and typical flight environmental conditions. IN-4 is classified as aviation technical equipment and is installed as a standard component of the AP-34B autopilot suite.
Alternate Designations:
IN-4 zero indicator may also appear as IN4, IN-4, ИН-4.
All notations refer to the same instrument.

Purpose: Visual indication of control signal deviations in the autopilot system
Systems: AP-34B automatic flight control and stabilization channels
Application: Mi-8, Mi-8T, Mi-8MT, Mi-8AMT, Mi-17
Product Type: Zero Indicator
Full deflection current: 300 ±50 μA
Pointer movement (downwards) current: 10 μA
Pointer start-up current: ≤0.02 mA
Power Supply: 27 V DC
Weight: ≤0.45 kg
Precious Metals Content: Gold ~0.223 g; Silver ~0.386 g
Category: Aviation Technical Equipment (ATE)
Mounting: Cockpit instrument panel
Condition: As applicable
Documentation: Passport (manufacturer certification)

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