BS-34-01

BS-34-1 unit in the AP-34B autopilot system

The BS-34-1 is an aircraft communication and signal-matching unit used in the AP-34B four-channel electrohydraulic autopilot system. This autopilot is installed on Mi-8, Mi-17, Mi-171 and related helicopter versions, depending on configuration. The BS-34-1 is not a cockpit control panel and not an actuator by itself. Its work is inside the autopilot signal chain: it helps connect, route and match electrical signals between sensors, control units and downstream autopilot equipment.

Signal matching through the BS-34-1 block

In the AP-34B system, the BS-34-1 supports signal interaction between sensor equipment and the units that process and amplify autopilot commands. Signals from angular rate sensors and related correction devices must be delivered in the correct form before they are used by the amplifier block and control unit. The BS-34-1 is used in this part of the circuit as a communication and matching element. If the block or its wiring is faulty, autopilot behavior may be affected even when the sensors and actuators themselves are serviceable.

Four autopilot channels handled by BS-34-1

The AP-34B autopilot works through several control channels, and the BS-34-1 is associated with signal communication in these channels. The main channels are roll, pitch, yaw and altitude. Each channel has its own sensor and control logic, but the autopilot must operate as a coordinated system rather than four separate circuits. The communication block helps maintain this coordination by supporting the transfer and matching of signals inside the autopilot architecture. This is why troubleshooting should always include the connected channels, not only the block itself.

BS-34-1 with AP-34B system components

The BS-34-1 operates together with the main AP-34B equipment group. This may include the autopilot control panel, control unit, BF-34 filter block, amplifier block, angular rate sensors and altitude correction equipment. In practical maintenance, the unit is checked together with its connectors, power supply, channel signals and the response of the autopilot during system tests. A failure may appear as loss of one channel, unstable operation, incorrect response to sensor input or interruption of signal transfer between the autopilot units.

Installation area of the BS-34-1 on Mi-8 helicopters

On Mi-8-type helicopters, the BS-34-1 is installed in the cargo cabin area, on the right side of the helicopter between frames No. 3 and No. 4. This location places the block within the onboard avionics and autopilot equipment layout rather than near the pilot controls. During inspection, attention is normally paid to mounting security, connector condition, wire harness routing, contamination, moisture traces and general housing condition. Since the block works in signal circuits, poor contact or wiring damage may be enough to disturb autopilot operation.

Power supply and operating readiness of BS-34-1

The BS-34-1 uses aircraft DC and AC power supply lines as part of the AP-34B system. After power-up, the block must be ready for normal operation within the specified readiness time. It is intended for continuous operation during flight when the autopilot system is in use. For service checks, technicians normally verify the supply voltages, connector integrity and correct channel behavior. If the autopilot does not pass system checks, the BS-34-1 should be examined together with the BF-34, amplifier block, control unit and angular rate sensors.

Ordering and documentation for BS-34-1

For procurement or replacement, the unit should be identified by the full designation BS-34-1 and by its documentation / drawing reference 6A2.390.070 TO. It is useful to specify whether the requirement is for a new unit, a storage item, a repaired unit or a checked first-category item. Since the block belongs to aircraft radio-electronic equipment, supply should include the available passport, label or technical documentation. Compatibility must be confirmed against the AP-34B modification, helicopter wiring diagram and the exact installed autopilot equipment set.

Product Type: Aircraft communication / signal-matching unit
Designation: BS-34-1
Documentation / Drawing Reference: 6A2.390.070 TO
Associated System: AP-34B four-channel electrohydraulic autopilot
Function: Electrical communication, signal matching and interaction between autopilot sensors and control equipment
Application / Where Used: Aircraft avionics and flight-control equipment
System / Installation Area: AP-34B autopilot equipment group
Compatible Aircraft / Equipment: Mi-8, Mi-17, Mi-171 and related helicopter versions equipped with AP-34B
Autopilot Channels: Roll, pitch, yaw and altitude
Associated Sensors: Angular rate sensors, depending on channel configuration
Associated Correction Equipment: KV-11 altitude corrector, depending on system configuration
Associated AP-34B Components: Autopilot control panel 6S2.390.007, control unit 6S2.399.000, BF-34 filter block, 1479V amplifier block, angular rate sensors
Signal Function: Conversion, matching and transfer of sensor signals before delivery to amplifier and autopilot control circuits
DC Power Supply: 27 V DC ±10%
AC Power Supply: 36 V AC ±5%
AC Frequency: 400 Hz
Readiness Time after Power-On: Not more than 2 minutes
Operating Mode: Continuous
Installation Location on Mi-8: Cargo cabin, right side, between frames No. 3 and No. 4
Supply Category: Aircraft radio-electronic equipment; condition and category according to available stock and documents
Technical Documentation: Product passport, AP-34B technical documentation, wiring diagrams and maintenance documentation as applicable

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