FLIGHT INSTRUMENTS
DIGITAL ELECTRONIC CLOCK
The Digital Electronic Clock (Figure 1-38) has three modes of operation:
• CLOCK MODE - This mode accumulates and displays time in hours, minutes, seconds, and indicates clock mode is in effect by a "C" showing on display below the seconds dig-ital indication.
• ELAPSED TIME MODE - This mode accumulates and dis-plays time counting upward in hours, minutes, and seconds, displays an illuminated sweep second hand, and indicates elapsed time mode is in effect by an "ET" showing on dis-play below seconds digital indication.
• TIME SET MODE - This mode is used to set time for clock mode and indicates time set mode is in effect by a flashing digit.
Two pushbuttons on front face of clock are used to select desired operating mode. The buttons are labeled "SEL" for select and
"CTRL" for control. These buttons have various functions, de-pending on which operating mode the clock is in (Figure 1-38).
The clock is powered by 28 VDC for the Standby Attitude Indi-cator (SAI) and 5 VAC background lighting from the auxiliary AC essential bus.
ADI.
The ADI (Figure 1-39), located on the instrument panel, pro-vides a display of aircraft pitch and bank attitude relative to the horizon. The ADI consists of a two-tone attitude sphere with graduated pitch references, fixed miniature aircraft, turn and slip indicator, pitch trim knob, pitch and bank steering bars, ADI off flag, glide slope deviation indicator and warning flag, and course warning flag. The ADI receives attitude information from either the HARS or EGI, as well as steering information from the EGI, TACAN, ILS, TISL, or FM homing, and displays it. The turn and slip indicator receives information only from the HARS, no matter which attitude reference system is selected. The EGI unit provides two- and three-dimensional navigation informa-tion used to drive the ADI steering bars and Glide Slope Indica-tor (GSI). See Figure FO-7 for additional information on navi-gation interfaces with the ADI. The ADI is powered by the right AC bus.
•
Certain EGI failures may cause incorrect in-formation to be displayed on the ADI bank steering bar without causing the ADI course warning flag to come into view when STR PT or ANCHR is selected on the NMSP. How-ever, these failures will cause the HSI bear-ing validity flag to come into view. Therefore, when STR PT or ANCHR is selected on the NMSP and the HSI bearing validity flag is in view, disregard the ADI bank steering bar indications. The ADI bank steering bar and course warning flag operate normally when TACAN, Instrument Landing System (ILS), Target Identification Set Laser (TISL), or FM HOMING is the selected source of the bank steering bar indications.•
Transitioning to instruments while flying with Night Vision Goggles (NVGs) may result in increased time required to discern aircraft al-titude from the ADL.HSI.
The HSI (Figure 1-40), located on the instrument panel, displays a plan view of navigation and positioning information. The HSI presents magnetic heading from the EGI or HARS, and relative bearing information from the EGI unit, TACAN and/or Auto-matic Direction Finder (ADF), command heading information, course information, Distance Measuring Equipment (DME) and TO-FROM indication relative to selected TACAN station or EGI steerpoint. The HSI also presents displacement of aircraft from selected course as computed by EGI unit, TACAN, or ILS.
See Figure FO-7 for additional information on navigation inter-faces with the HSI. The HSI compass card, bearing pointer, and course deviation indicator are powered by the right AC bus.
ADI and HSI Power Off Warning Flags.
During normal operation, the ADI and HSI power OFF flags will be in view under any of the following conditions:
• During the initial start cycle for approximately 90 seconds when HARS Δ indicator is lit on NMSP
• Whenever the HARS FAST ERECT switch is depressed when HARS Δ indicator is lit on NMSP
• During heading synchronization in the SLAVE mode when HARS Δ indicator is lit on NMSP.
A power OFF flag in view in either or both instruments, other than those listed above, indicates a malfunction. See Figure
FO-7 for additional information on the ADI and HSI power OFF flags.
Failure of certain components can result in er-roneous or complete loss of attitude and heading presentations without a visible OFF flag. It is im-perative that the ADI and HSI be cross-checked with other flight instruments when under actual or simulated instrument conditions.
Figure 1-38. Digital Electronic Clock (Sheet 1 of 3)
MODE Control or Indicator Position or Display Function
Clock Sel Depress Changes Operating Mode From Clock To Elapsed Time.
Ctrl Depress No Function In Clock Mode.
SEL & CTRL Depress Changes operating mode from clock to time set.
simultaneously
NOTE
While in clock mode, elapsed time continues to function.
ELAPSED TIME SEL Depress Changes operating mode from elapsed time to clock.
CTRL Depress Controls elapsed time function by starting, stopping, or resetting to zero. Consecutively depressing and releasing "CTRL" will cycle elapsed time as follows:
"start-stop-zero-start"
NOTE
While in elapsed time mode, elapsed time continues to function.
TIME SET SEL Depress Changes which digit is flashing, awaiting setting.
CTRL Depress Increments by one, the digit which is flashing.
NOTE
While in time set mode, clock time is stopped and elapsed time continues to function.
Operational Procedure Self-Test
The clock during the first 5 seconds of operation, illuminates all of the segments. Check to see if all segments are illuminated.
The clock will then start up in formal time mode.
Time Set Sequence
Enter set time mode: Depress SEL & CTRL simultaneously during clock mode (Hrs digits flash) Depress CTRL: Hours will increment
Depress SEL: Minutes will flash Depress CTRL: Minutes will increment Depress SEL: Seconds will flash Depress CTRL: Seconds will increment Depress SEL: Returns to normal clock mode
Figure 1-38. Digital Electronic Clock (Sheet 2)
Selecting Elapsed Time (ET) & Clock Modes (C)
Depress SEL: Clock changes to elapsed mode (ET) Depress SEL: Clock changes to clock mode (C) Elapsed Time Operation
Depressing CTRL in Elapsed Time Mode (ET) 1st - Starts Elapsed Timer 2nd - Stops Elapsed Timer 3rd - Resets Elapsed Timer 4th - Repeats cycle (Starts)
Figure 1-38. Digital Electronic Clock (Sheet 3)
Figure 1-39. Attitude Directional Indicator (ADI)
Figure 1-40. Horizontal Situation Indicator