BKK-18

BKK-18 roll monitoring unit in aircraft systems

The BKK-18 is an aircraft roll monitoring unit used in onboard flight and navigation equipment. It continuously monitors aircraft roll angle and checks the serviceability of the main attitude reference instruments during flight. The unit is used in aircraft and helicopters equipped with several independent artificial horizons or gyro-vertical units. Its role is not to display attitude directly to the pilot, but to compare roll signals, detect disagreement between channels and issue warning or failure signals to the cockpit systems.

Monitoring of artificial horizon serviceability

The BKK-18 compares roll signals received from three independent attitude sources: left, right and standby artificial horizons or gyro-vertical channels, depending on the aircraft configuration. If one of the instruments begins to differ critically from the other two, the unit identifies the failed channel and generates a corresponding failure signal. This helps the aircraft system isolate the unreliable attitude source and prevents the crew or connected avionics from relying on incorrect roll data. This function is especially important in multi-channel flight instrument systems.

Roll limit warning function

In addition to monitoring attitude source agreement, the BKK-18 supervises the current roll angle of the aircraft or helicopter. When the roll angle reaches a preset limit, the unit forms a warning signal for the crew. Depending on system wiring, this may be displayed as left or right excessive roll indication and may also trigger an aural warning. The warning threshold can be different for flight phases, such as approach / landing and route flight, where allowable bank angles are not the same.

Operating thresholds and flight mode logic

The BKK-18 supports different roll warning thresholds. The lower threshold is used for approach or landing mode, while the higher threshold is used for route flight. Mode switching can be performed automatically or by command from the aircraft system through a 27 V control signal. This allows the aircraft to use tighter roll limits during critical flight phases and wider limits during normal en-route operation. The unit also monitors disagreement between attitude channels and generates failure signals when the difference exceeds the specified limit.

Signal outputs and cockpit warnings

When abnormal roll conditions or attitude instrument disagreement are detected, the BKK-18 sends signals to the aircraft warning and indication circuits. Typical signals include failure of the left, right or standby artificial horizon, excessive left or right roll warning and general excessive roll aural warning. Depending on the aircraft type, these signals may go to cockpit annunciators, warning panels, buzzers or voice warning equipment. The exact indication format depends on the aircraft wiring and installed cockpit warning system.

Design and redundancy of BKK-18

The BKK-18 is built as a duplicated control unit with two independent internal sub-blocks. This design reduces the risk of false triggering and supports reliable monitoring of roll warning and attitude source failure conditions. The unit is designed to work with different types of attitude instrument output sensors, including selsyn transmitters, potentiometric sensors and sine-cosine transformers. This makes it suitable for several aircraft configurations, provided that the installation is approved by the aircraft documentation.

Maintenance and adjustment of BKK-18

The BKK-18 is checked and adjusted using specialized test equipment, including the PAP-32 test panel. During maintenance, technicians verify roll warning thresholds, artificial horizon failure detection, signal outputs, power supply and internal channel operation. Since the unit works in safety-related warning circuits, correct adjustment is important. A false warning can distract the crew, while a missed warning can leave a hazardous roll condition or attitude instrument failure undetected. For replacement, the unit should be checked against the aircraft wiring diagram and maintenance documentation.

Product Type: Roll monitoring unit / attitude monitoring unit
Designation: BKK-18
Cyrillic Designation: БКК-18
Function: Monitoring of aircraft roll angle and serviceability of artificial horizons / gyro-vertical units
Application / Where Used: Aircraft and helicopter flight and navigation instrument systems
System / Installation Area: Onboard attitude monitoring and roll warning circuits
Compatible Aircraft / Equipment: Yak-42, Tu-134, Tu-154, Mi-8 / Mi-17 family helicopters and other aircraft depending on configuration
Monitored Attitude Sources: Three independent attitude channels: left, right and standby artificial horizon / gyro-vertical units
Artificial Horizon Failure Threshold: ±7° ±2° disagreement threshold
Roll Warning Threshold, Landing Mode: ±15° ±2.5°
Roll Warning Threshold, Route Mode: ±33° ±4°
Mode Switching: Automatic or manual by +27 V aircraft control signal
Power Supply: 36 V AC, single-phase, 400 Hz
Warning / Signalling Circuit Supply: 27 V DC
Sensor Compatibility: Selsyn, potentiometric or sine-cosine transformer outputs depending on aircraft system
Output Signals: Left / right / standby artificial horizon failure; excessive left / right roll; excessive roll warning
Design: Duplicated unit with two independent internal sub-blocks
Maintenance Equipment: PAP-32 test panel for checking and adjustment
Construction Features: Electronic modules with protected printed circuit boards; designed for aircraft environmental conditions
Condition: As applicable
Technical Documentation: Product documentation / maintenance documentation available upon request

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Warranty
All products are covered by a standard 6-month warranty.
Extended warranty is available upon request and is agreed individually; it may affect the final product price.