Three BDHIs (Figure 1-14-17) are installed in the CH124B helicopter, two in the cockpit instrument panel, and one on the sensor station.

The BDHI consists of a rotating compass card calibrated to 360 degrees in 5 degree increments, a fixed index at the top of the indicator face, a singlebarred (No.1) pointer, a double-barred (No.2) pointer and a three-digit range counter.

The compass card on the pilot’s, co-pilot’s and TACCO’s BDHIs will display either magnetic heading of the helicopter from the GHARS, ground track information from the AN/ASN-123C system or true heading information from the GHARS, depending upon which CARD selection is made on the BDHI selector panel.

The pilot’s, co-pilot’s and TACCO’s BDHI No.1 pointer will indicate LF ADF bearing information, UHF ADF bearing information, VHF/AM ADF bearing information, VHF/FM ADF bearing information, OTPI sonobuoy bearing information or AN/ASN-123C readout information in true or magnetic, depending on the selection made on the BDHI selector panel, ARA selector panel and OTPI control panel.

The pilot’s, co-pilot’s and TACCO’s BDHI No.2 pointer will indicate either magnetic or true TACAN or VOR bearing dependent upon the CARD selection on the BDHI selector panel.

The three-digit range counter on the BDHI displays AN/ASN-123C distance information with ASN selected or TACAN DME with ARN/TAC or ARA/TAC selected on the BDHI control panel. The IND ØB circuit-breaker on the Radio Circuit-breaker Panel provides the power to the synchronization signal that enables the BDHI to display magnetic or true heading, bearing information (No.1 and No.2 needles) and TACAN distance.