Narrative:

Over the past two months I have experienced GPS outage approaching mkjp when approaching from the north or west and below 10000 ft. This is occurring on each of approximately 20 arrivals; but never on departure. My suspicions are that there is some type of radio frequency (emf) interference that is desensitizing our GPS. The GPS is part of a late model universal avionics uns-1L FMS system. This event has never happened at any other airports. This event occurs over the mountains to the west or north of the airport. I am able to reboot the FMS and obtain reception and good position while closer to the airport; ie; no longer over the higher terrain where there appear to be radio towers on mountain peaks or ridges. It is not possible to conduct a GPS based approach at mkjp.callback conversation with reporter revealed the following information: the reporter stated that the typical routing clearance is from the fir boundary on A301 to either elser or keyno intxns for a VOR or ILS approach. When over land north and west of the airport the GPS signal is lost causing an FMS disruption requiring a reboot. This has occurred the last 20 times this aircraft has approached mkjp. The reporter suspects that there may be emf radiation from the mountains beneath the track that the routing covers. The highest terrain in this area is around 3400 ft and for the most part the aircraft is in clouds at this point so GPS contributes greatly to situational awareness. On the north east side of mkjp the terrain rises rapidly to 7400 ft with an additional mountain at 3315 ft about 6 NM from the departure end of runway 12. The crew had been rebooting the GPS in order to maintain RNAV and accurate mapping during the approach and in the event of a go around or missed approach.

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Original NASA ASRS Text

Title: A CORP ACFT USING A UNS-1L FMS LOSES GPS RECEPTION WITHIN 30 NM WHEN NORTH AND WEST OF MKJP/KIN.

Narrative: OVER THE PAST TWO MONTHS I HAVE EXPERIENCED GPS OUTAGE APPROACHING MKJP WHEN APPROACHING FROM THE NORTH OR WEST AND BELOW 10000 FT. THIS IS OCCURRING ON EACH OF APPROXIMATELY 20 ARRIVALS; BUT NEVER ON DEPARTURE. MY SUSPICIONS ARE THAT THERE IS SOME TYPE OF RADIO FREQUENCY (EMF) INTERFERENCE THAT IS DESENSITIZING OUR GPS. THE GPS IS PART OF A LATE MODEL UNIVERSAL AVIONICS UNS-1L FMS SYSTEM. THIS EVENT HAS NEVER HAPPENED AT ANY OTHER AIRPORTS. THIS EVENT OCCURS OVER THE MOUNTAINS TO THE WEST OR NORTH OF THE AIRPORT. I AM ABLE TO REBOOT THE FMS AND OBTAIN RECEPTION AND GOOD POSITION WHILE CLOSER TO THE AIRPORT; IE; NO LONGER OVER THE HIGHER TERRAIN WHERE THERE APPEAR TO BE RADIO TOWERS ON MOUNTAIN PEAKS OR RIDGES. IT IS NOT POSSIBLE TO CONDUCT A GPS BASED APPROACH AT MKJP.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT THE TYPICAL ROUTING CLRNC IS FROM THE FIR BOUNDARY ON A301 TO EITHER ELSER OR KEYNO INTXNS FOR A VOR OR ILS APCH. WHEN OVER LAND NORTH AND WEST OF THE ARPT THE GPS SIGNAL IS LOST CAUSING AN FMS DISRUPTION REQUIRING A REBOOT. THIS HAS OCCURRED THE LAST 20 TIMES THIS ACFT HAS APCHED MKJP. THE REPORTER SUSPECTS THAT THERE MAY BE EMF RADIATION FROM THE MOUNTAINS BENEATH THE TRACK THAT THE ROUTING COVERS. THE HIGHEST TERRAIN IN THIS AREA IS AROUND 3400 FT AND FOR THE MOST PART THE ACFT IS IN CLOUDS AT THIS POINT SO GPS CONTRIBUTES GREATLY TO SITUATIONAL AWARENESS. ON THE NORTH EAST SIDE OF MKJP THE TERRAIN RISES RAPIDLY TO 7400 FT WITH AN ADDITIONAL MOUNTAIN AT 3315 FT ABOUT 6 NM FROM THE DEPARTURE END OF RWY 12. THE CREW HAD BEEN REBOOTING THE GPS IN ORDER TO MAINTAIN RNAV AND ACCURATE MAPPING DURING THE APCH AND IN THE EVENT OF A GAR OR MISSED APCH.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.