BKK-18

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.