BI-037D

BI-037D measuring board in the A-037 radio altimeter

The BI-037D is an electronic measuring unit used inside airborne radio altimeter equipment. It is included in the radio component set of the A-037 radio altimeter and works in receiver configurations such as A-037-1A, A-037-1V and A-037-1G, as well as in the PP-5M receiver. The BI-037D is not a standalone device. It is an internal printed circuit board that operates together with the transmitting, receiving and power-supply modules of the complete radio altimeter system.

Measurement-channel role of BI-037D

The BI-037D works in the receiving and measuring channel of the radio altimeter. Its task is to process the measurement signals formed during radio altimeter operation. In practical terms, the board receives the beat-frequency signal path after the microwave receiving section and low-frequency amplification stages, then participates in filtering, amplification, pulse-frequency processing and formation of altitude-related output signals. The board does not transmit microwave energy and does not display height in the cockpit by itself.

BI-037D with M51102-1 and M45110-1 modules

In the A-037 radio altimeter, the BI-037D works together with microwave modules such as the M51102-1 transmitting module and the M45110-1 receiving module. The transmitting module forms the frequency-modulated microwave signal, while the receiving module extracts the beat-frequency signal from the reflected return. The BI-037D then processes this measurement signal and helps form outputs used by the cockpit height indicator and connected onboard systems. Because of this, the board should be checked as part of the complete radio altimeter signal chain.

Output signals of the BI-037D board

The BI-037D is associated with the formation of altitude output signals used by the A-037 equipment. These may include analog DC height outputs such as H1+ for the cockpit pointer indicator and H3+ for connected onboard systems, depending on the aircraft configuration. The board may also participate in formation of failure and danger-height signals. The exact output logic, scaling and permissible error should be confirmed by the A-037 technical documentation, because the BI-037D works as part of the complete system rather than as an individually calibrated standalone unit.

BI-037D modification and operating range

The BI-037D is described as a measuring board variant with output scaling adapted for the operating logic of the A-037 system. The measuring range is associated with the low-altitude range of the system, commonly up to 300 meters for the relevant configurations. Compared with earlier BI-037 / BI-037A boards, the BI-037D may differ by analog signal output range and scaling algorithm. For replacement, it is important to confirm the exact board version, receiver type, system variant and aircraft documentation.

Control functions in the microwave channel

The BI-037D may also include circuits related to transmitter control. These circuits can form the low-frequency modulation voltage used to control the transmitting microwave module through the tuning element. The board may also participate in maintaining modulation stability and correct measurement-channel behavior. Since these functions influence the radio altimeter’s ability to form a valid height signal, an incorrect BI-037D board or a faulty modulation section can lead to unstable indication, TEST failure or false fault signals.

Installation and supply of BI-037D

The BI-037D is manufactured as an electronic printed circuit board installed inside radio altimeter receiver assemblies. It should be handled as an avionics board, with attention to connector condition, soldering, corrosion, contamination, static protection, storage history and compatibility with the target equipment. For procurement, the full designation BI-037D should be used. Alternative names such as BI 037D, BI-037 D or BI037D can help identify the item, but final matching should be made by documentation and equipment configuration.

Product Name: Measuring Unit
Part Number: BI-037D
Product Type: Measuring unit / electronic printed circuit board
Function: Operation within the radio altimeter measurement channel
System Application: A-037 radio altimeter
Compatible Receivers: A-037-1A; A-037-1V; A-037-1G
Additional Application: PP-5M receiver
Main Operating Role: Processing of measurement signals in the receiving and measuring channel
Related Microwave Modules: M51102-1 transmitting module; M45110-1 receiving module, depending on configuration
Associated Signal Path: Beat-frequency / low-frequency measurement signal path
Possible Output Signals: H1+ analog height output; H3+ system output; failure and danger-height signals, depending on configuration
Measurement Range: Defined by A-037 system configuration; commonly associated with 0–300 m range for relevant versions
Basic Technical Data: Defined at A-037 system level
Power Supply: Supplied from internal A-037 power circuits / BP-037 sub-block, depending on equipment design
Design: Electronic printed circuit board
Operation Mode: Installed inside radio altimeter equipment; not used as a standalone device
Condition: As applicable
Alternate Designations: BI-037D; BI 037D; BI-037 D; BI037D
Technical Documentation: A-037 radio altimeter documentation and applicable receiver documentation

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