BSGO-400A

BSGO-400A main rotor speed warning unit

The BSGO-400A is an aircraft warning unit used for monitoring main rotor speed on helicopters. It is part of the onboard indication and warning equipment, not a rotor control unit. The block receives speed information from the main rotor RPM sensing circuit and compares the current value with preset limits. If the rotor speed moves outside the allowed range, the unit gives a warning command to the cockpit indication system. For the crew, this is one of the warning channels that helps track rotor operating limits during flight and engine operation.

Limit monitoring through BSGO-400A

In operation, the BSGO-400A monitors both low and high main rotor speed conditions. A low-speed warning is used when rotor RPM drops below the permitted level, which can happen during abnormal engine power conditions or incorrect rotor loading. A high-speed warning is used when the rotor exceeds the allowed upper limit. The unit itself does not correct rotor speed and does not act on the engines. It only processes the incoming signal and sends the corresponding warning command to the aircraft indication circuits.

Main rotor RPM signal processing in BSGO-400A

The input signal normally comes from the main rotor speed sensor or from the related RPM measuring circuit. The signal frequency is proportional to rotor speed, and the electronic section of the unit compares it with internal reference thresholds. In older descriptions, this logic may be explained through monostable circuits or a dedicated calculating section. For maintenance, the whole chain matters: sensor condition, wiring, connectors, the BSGO unit, cockpit lamps, and power supply. A missing warning is not always caused by the warning unit itself.

Helicopter application of unit BSGO-400A

The BSGO-400A is used on helicopter types where main rotor RPM limit warning is required. Typical applications include Mi-8 / Mi-17 / Mi-171 family helicopters and Ka-32-type installations, depending on the onboard equipment set and modification standard. Installation location can differ by helicopter version. In some configurations the unit may be placed near electrical panels, in the radio compartment, or in another equipment bay defined by the aircraft documentation. Before replacement, the installed part should be checked against the aircraft parts catalog and wiring diagram.

Identification and ordering checks for BSGO-400A

Before ordering, the marking on the installed unit should be compared with the helicopter maintenance documentation, parts catalog, or overhaul records. Helicopters of the same family may have different warning system layouts after repair or modernization. It is useful to provide the unit designation, helicopter type, installation location, and a photo of the data plate. The product is also known under alternative designation БСГО-400А.

Product Type: Main rotor limit RPM warning unit
Function: Automatic monitoring of main rotor RPM limits and cockpit warning signal output
Application / Where Used: Helicopter rotor speed warning and indication systems
System / Installation Area: Main rotor RPM monitoring / cockpit warning indication circuit
Compatible Aircraft / Equipment: Mi-8, Mi-17, Mi-171, Mi-171E, Ka-32 and applicable modifications
Input Signals: Signal from main rotor RPM sensor / RPM measuring circuit
Output Signals: Warning commands for cockpit indication lamps
Warning Indications: Main rotor RPM low; main rotor RPM high
Lower Warning Threshold: Approx. 92% of nominal rotor RPM, depending on aircraft configuration
Upper Warning Threshold: Approx. 98% of nominal rotor RPM, depending on aircraft configuration
Technical Documentation: Helicopter maintenance documentation / aircraft warning system documentation

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