Garmin GNC 420, Pilot'S Manual & Reference

Page: 245 / 258

GNC 420(A) Pilot’s Guide and Reference
APPENDIX C
TROUBLESHOOTING
C-1
APPENDIX C: TROUBLESHOOTING
Q & A
This section is designed to answer some of the
common questions regarding the GNC 420’s capabilities
and operation. If there is a problem operating the unit,
read through this appendix and refer to the reference
section noted. If the answer to a particular question is
not covered here, use the index to find the appropriate
section elsewhere in this manual. If, after reading through
the appropriate reference section, the answer cannot be
found, please see an authorized dealer or contact Garmin
directly at the address or phone numbers listed on page
ii. Garmin is dedicated to supporting its products and
customers.
What is RAIM, and how does it affect approach
operations?
RAIM is an acronym for Receiver Autonomous Integrity
Monitoring, a GPS receiver function that performs a
consistency check on all tracked satellites. RAIM ensures
that the available satellite geometry allows the receiver
to calculate a position within a specified protection limit
(4 nm for oceanic, 2 nm for enroute, 1 nm for terminal
and 0.3 nm for non-precision approaches).
During oceanic, enroute, and terminal phases of flight,
RAIM is available nearly 100% of the time. Because of
the tighter protection limit on approaches, there may
be times when RAIM is not available. The GNC 420
automatically monitors RAIM and warns the pilot with an
alert message (Section 13) when it is not available, and
the INTEG annunciator appears at the bottom left corner
of the screen. If RAIM is not available when crossing the
FAF, the pilot must fly the
missed approach procedure.
The GNC 420’s RAIM prediction function (Section 12)
also allows the pilot to see whether RAIM is available for a
specified date and time.
NOTe: if raiM is not predicted to be available for
the final approach course, the approach does not
become active—as indicated by an ‘approach is
not active’ message, a ‘raiM not available from
FaF to MaP’ message, and iNTeG annunciator.
Why aren’t there any approaches available for
my flight plan?
Approaches are available for the final destination
airport in a flight plan or as a direct-to (keep in mind
that some VOR/VORTAC identifiers are similar to airport
identifiers). If a destination airport does not have a
GPS approach, the GNC 420 indicates ‘NONE’ for the
available procedures—as listed on the Airport Approach
Page (Figure C-1). For more information on selecting an
approach, see Section 6.1.
Figure C-1 Airport Approach Page
190-00140-20 Rev. K