When the NAV radio is tuned to an ILS frequency the bearing source and
the bearing pointer is removed from the HSI. When NAV1 or NAV2 is the
selected bearing source, the frequency is replaced by the station identier
when the station is within range. If GPS is the bearing source, the active
waypoint identier is displayed instead of a frequency.
COURSE DEVIATION INDICATOR (CDI)
The Course Deviation Indicator (CDI) moves left or right from the course
pointer along a lateral deviation scale to display aircraft position relative to the
course. If the course deviation data is not valid, the CDI is not displayed.
Figure 7-19 – Course Deviation Indicator
NOTE: During a heading change of greater than 105° with respect to
the course, the CDI on the Arc HSI switches to the opposite side of the
deviation scale and displays reverse sensing.
CDI
Navigation
Source
CDI
Scale
Flight
Phase
Arc HSI
Crosstrack
Error
Navigation
Source
Scale
CDI
360
I
Flight
Phase
NOTE: When crossing over the nal waypoint in a ight plan, the to/from
indicator will show a “from” indication and the NAV status bar will show a
180° change in course, but a “direct-to” the last waypoint in the ight
plan may still be shown in the PFD Navigation Status Box. Furthermore, if
the autopilot is engaged in a NAV mode, it will continue to navigate away
from the waypoint on the course shown on the head of the CDI needle.