The pilot and co-pilot CDIs provide visual indication of off-course deviations from the helicopter course to, or from, a navigation beacon, and glide slope deviations in ILS mode. The components of the course direction indicator, used with the TACAN VOR/ILS systems are the vertical pointer, a warning flag, ambiguity flag, a rotating pointer and degreecalibrated dial face, a set-in course knob and a three digit course window, a horizontal pointer, marker lamp and glide slope warning flag (Figure 1-11-9). The function of controls are as follows:
a. Vertical Pointer. If the helicopter is off course, the vertical pointer automatically positions to the left or to the right of the centre of the indicator dial face, visually indicating the helicopter deviation from the set-in course (TACAN or VOR only).
b. Horizontal Pointer. Active only in ILS mode, the bar provides indications relative to the glide path. Full-scale deflection, up or down represents a deviation of greater than 1/2 degree from the normal glide path. In TACAN or VOR modes, the pointer is centred with the OFF flag displayed.
c. Marker Light. If the CDI is the command instrument, pending NAV selection (TACAN or VOR/LOC), Course Control switch (PCONT or CPCONT) and appropriate radio, the green marker light will illuminate (Figure 1-11-9).
d. Warning Flags;
(1) Vertical Pointer. If the selected TACAN, VOR or LOC signal is not valid, an OFF flag will appear at the top of the pointer.
(2) Horizontal Pointer. Active only in ILS mode, an OFF flag will appear if the glide path signal is not valid. In TACAN or VOR, the OFF flag is visible.
e. Indicator Dial Face. Calibrated in degrees, first mark equals 5 degrees, second mark equals 10 degrees and full scale represents 45 degrees of azimuth from centre for TACAN or VOR signals.
f. Rotating Pointer. The rotating pointer indicates on the calibrated dial face the difference (relative heading) in degrees between the magnetic heading of the helicopter and the set-in course displayed in the COURSE window for TACAN and VOR. The course selection has no effect on ILS localizer signals.
g. SET Knob. The set-in knob, marked “SET”, at the lower left corner of the instrument, permits the pilot to set in the desired course to fly to reach the selected destination.
h. COURSE Window. Numerically displays the set-in course and is located at the top of the indicator.
i. Ambiguity Flag. The ambiguity flag appears in a small window at the upper left side of the indicator and will display either the word TO or FROM, depending on whether the set-in course is toward or away from a TACAN or VOR station. In ILS mode it is not active.
