5-18 Abnormal Procedures
NAV INVALID
Failure Indication:
If the DFC-PFD system recognizes that the VHF lateral nav signal
from the GPS Nav-Com is invalid, a yellow “NAV INVALID”
message is displayed on the PFD. In addition, the Horizontal
Deviation Indicator (HDI)/Lateral Deviation Indicator (LDI) along
the bottom edge of the ADI will be Red-X’d.
The autopilot will command a wind corrected course hold and, if
sufficient power is available, the flight path angle at the time the
system displayed “NAV INVALID”.
Functionality Lost:
The ability to track a VHF lateral course (VOR or Localizer) from
the selected GPS Nav-Com navigator has been lost.
Recommended Pilot Action:
Consider switching the navigator that is driving the PFD CDI and
autopilot.
If unable to select a usable alternative navigation source, take the
proper action when a navigation source has been lost. If on a
published approach that requires VHF-based lateral guidance,
the approach must be terminated.
Consider switching to GPSS or Heading modes of the autopilot
for lateral mode operations.
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