Electronic Horizontal Situation Indicator (14.6)
The EHSI presents a selectable, dynamic colour display of flight progress with plan view orientation. The EHSI has a number of different modes of operation which can be selected by the flight crew. The number of modes is dependent on the system fitted.
Figure 7 shows an EHSI display in Rose mode.
EHSI display in Rose mode
Figure 6
14.6.1 Control Panel
Allows the crew to select the required display configuration and what information is to be displayed. Both Captain and Co-Pilot have their own display controllers. The controllers have two main functions:
Display Controller: Selects the display format for EHSI as FULL, ARC, WX or MAP.
Source Select: Selects the system that will provide information required for display. The source information will be VOR, ADF, INS, FMS, VHF and NAV.
EFIS Display Controller and the Source Controller is shown at Figure 7.
EFIS Display and Source Controller
Figure 7
14.6.2 EFIS Symbol Generator
These provide the analog, discrete and digital signal interfaces between the aircraft’s systems, the display units and the control panel. They provide symbol generation, system monitoring, power control and the main control functions of the EFIS overall.
Figure 8 shows the EFIS units and signal interface in block schematic form
EFIS Block Schematic
Figure 8
14.6.3 Testing
Test is controlled from the DH/TEST knob located on the EFIS control panel. The test, if carried out using the First Officer’s control panel, will have the following effect on the Captain’s EADI:
1. Runway symbol will fall.
2. Rad Alt digital display indicates 95 to 100 feet.
3. The First Officer’s EADI warning will be activated:
4. Amber dashes are displayed on the Rad Alt digital display.
5. Amber dashes are displayed on the selected DH digital display.
When the TEST button is pressed on the Captain’s EFIS control panel the same test sequence takes place. The test altitude value remains displayed as long as the TEST button is pressed. Releasing the knob causes actual altitude to be displayed and digits of the DH display to show the selected value at the end of the test. The test sequence can be initiated during flight except during APP (Approach).