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APPENDIX C
Troubleshooting Q & A
207
What is RAIM, and how does it affect approach opera-
tions? 
RAIM is an acronym for Receiver Autonomous Integ-
rity Monitoring, a GPS 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 
(2.0 nautical miles for oceanic and en route, 1.0 NM for 
terminal and 0.3 NM for non-precision approaches). 
During oceanic, en route 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 500W-series unit 
automatically monitors RAIM and warns you with an alert 
message (see Section 12) 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 500W-series unit RAIM prediction func-
tion (see Section 9 Aux Pages - Utility Page - RAIM Predic-
tion
) also allows you to see whether RAIM will be available 
for a specified date and time. 
 
NOTE: RAIM prediction is not directly related to 
WAAS integrity. 
RAIM integrity prediction is performed by the 
internal GPS receiver and is performed at all times. 
WAAS integrity is reported by the WAAS satellite 
system and only works within the WAAS service 
volume. WAAS approaches require WAAS integrity. 
Outside of the WAAS service volume, such as an Oce-
anic flight, RAIM prediction will be used. 
Appendix C   
Troubleshooting Q & A
This Appendix is designed to answer some of the 
common questions regarding the 500W-series capa-
bilities and operation. If you have a problem operating 
the unit, read through this appendix and refer to the 
reference section noted. If you don’t find answers to 
your particular question here, use the index to find the 
appropriate section elsewhere in this manual. If, after 
reading through the appropriate reference section, you 
still haven’t found the answer to your question, please 
see your 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.