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APPENDIX F
Troubleshooting Q & A
Appendix F
Troubleshooting Q & A
The GPS 155 is a precision navigation instrument that offers a wide array of per-
formance navigation features. The ‘Q & A’ section is designed to answer some of the
common questions regarding the GPS 155’s capabilities and operation. If you have a
problem operating your unit, go through the troubleshooting section and refer to the
reference section noted. If your problem is not listed in the Q & A section, use the
index to find the appropriate reference in the manual. If you still encounter a prob-
lem, please see your authorized dealer or call or fax our customer support staff at
913-599-1515 or 913-599-2377 FAX. GARMIN is dedicated to supporting its prod-
ucts and customers.
What is RAIM, and how does it affect approach operations?
RAIM is an acronym for Receiver Autonomous Integrity Monitoring, a receiver
function that performs a consistency check on all tracked satellites. RAIM ensures
that the available satellite geometry will allow the receiver to calculate a position
within a specified protection limit (2 nm for oceanic and en route, 1 nm for terminal
and 0.3 nm for non-precision approaches).
During oceanic, enroute and terminal phases of flight, RAIM will be nearly 100%.
Because of the tighter protection limit on approaches, there may be times when RAIM
is not available. The GPS 155 automatically monitors RAIM and will warn you with
an alert message (see Appendix C) when it is not available. If RAIM is not available
when crossing the FAF, the ACTV annunciator will not illuminate and the pilot must
fly the missed approach procedure. The GPS 155’s RAIM prediction function (see
page 20) will also allow you to see whether RAIM will be available for a specified
date and time.
155man (GOOD) 7/24/98 1:57 PM Page 111