Narrative:

Using GPS (kln 90B certified) to navigation I was instructed to proceed direct to bld (boulder VOR). The GPS showed a heading of 090 degrees, I proceeded on that track to the VOR. The heading was direct to an aircraft on the arrival into las vegas, mc carran airport. I was climbing through the aircraft altitude and the controller advised that I was approximately 20 degrees to the left of my intended course. I then reverted to using the VOR as my primary means of navigation. I did fail to advise ATC of my impairment of GPS navigation functions at that time. My primary objective was to resolve the navigation problem I was having with my equipment. Within 20 NM/3 mins the GPS was again concurring with VOR navigation signals as regard position. No error messages were displayed on the GPS. A GPS NOTAM was prevalent within a 300 NM radius of tcc VOR to take effect 25 mins after this time. Reliance on GPS equipment as a sole means of navigation can present problems. The problem was resolved within 10 seconds from advice from controller. I had two means of navigation providing conflicting information. This is not the first time this problem has arisen. Callback conversation with reporter revealed the following information: reporter states that he was on a SID out of las heading to phx. He did have the RMI set up for VOR reference but one does tend to rely on the GPS as it is usually reliable. Controller indicated he was 10 mi off course. He immediately referenced the VOR indications and corrected. This GPS has had troubles before and was sent back to the manufacturer. The problem was a faulty card, part of the integrated circuit board. It was repaired and returned but still seems to have some problems. The manufacturer has had some difficulty with these units. Company procedure is to always carry the manual in the aircraft and abide by proper usage procedures. Reporter does carry a hand-held as backup and has no trouble with it. The 2 units do disagree at times. Reporter states that he has had more than this one experience of being off course with the GPS and it even showed him in mexico at one time. He vehemently states that the FAA should not even consider doing away with the VOR navaids since there would then be no backup at all.

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Original NASA ASRS Text

Title: FLC OF C441G USING GPS NAV IS NOTED TO BE OFF COURSE BY ATC. FLC GOES TO VOR BACKUP AND RETURNS TO COURSE. GPS HEADING TOOK THEM DIRECTLY TOWARD AN ACFT ON ARR.

Narrative: USING GPS (KLN 90B CERTIFIED) TO NAV I WAS INSTRUCTED TO PROCEED DIRECT TO BLD (BOULDER VOR). THE GPS SHOWED A HDG OF 090 DEGS, I PROCEEDED ON THAT TRACK TO THE VOR. THE HEADING WAS DIRECT TO AN ACFT ON THE ARR INTO LAS VEGAS, MC CARRAN ARPT. I WAS CLBING THROUGH THE ACFT ALT AND THE CTLR ADVISED THAT I WAS APPROX 20 DEGS TO THE L OF MY INTENDED COURSE. I THEN REVERTED TO USING THE VOR AS MY PRIMARY MEANS OF NAV. I DID FAIL TO ADVISE ATC OF MY IMPAIRMENT OF GPS NAV FUNCTIONS AT THAT TIME. MY PRIMARY OBJECTIVE WAS TO RESOLVE THE NAV PROB I WAS HAVING WITH MY EQUIP. WITHIN 20 NM/3 MINS THE GPS WAS AGAIN CONCURRING WITH VOR NAV SIGNALS AS REGARD POS. NO ERROR MESSAGES WERE DISPLAYED ON THE GPS. A GPS NOTAM WAS PREVALENT WITHIN A 300 NM RADIUS OF TCC VOR TO TAKE EFFECT 25 MINS AFTER THIS TIME. RELIANCE ON GPS EQUIP AS A SOLE MEANS OF NAV CAN PRESENT PROBS. THE PROB WAS RESOLVED WITHIN 10 SECONDS FROM ADVICE FROM CTLR. I HAD TWO MEANS OF NAV PROVIDING CONFLICTING INFO. THIS IS NOT THE FIRST TIME THIS PROB HAS ARISEN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HE WAS ON A SID OUT OF LAS HEADING TO PHX. HE DID HAVE THE RMI SET UP FOR VOR REF BUT ONE DOES TEND TO RELY ON THE GPS AS IT IS USUALLY RELIABLE. CTLR INDICATED HE WAS 10 MI OFF COURSE. HE IMMEDIATELY REFED THE VOR INDICATIONS AND CORRECTED. THIS GPS HAS HAD TROUBLES BEFORE AND WAS SENT BACK TO THE MANUFACTURER. THE PROB WAS A FAULTY CARD, PART OF THE INTEGRATED CIRCUIT BOARD. IT WAS REPAIRED AND RETURNED BUT STILL SEEMS TO HAVE SOME PROBS. THE MANUFACTURER HAS HAD SOME DIFFICULTY WITH THESE UNITS. COMPANY PROC IS TO ALWAYS CARRY THE MANUAL IN THE ACFT AND ABIDE BY PROPER USAGE PROCS. RPTR DOES CARRY A HAND-HELD AS BACKUP AND HAS NO TROUBLE WITH IT. THE 2 UNITS DO DISAGREE AT TIMES. RPTR STATES THAT HE HAS HAD MORE THAN THIS ONE EXPERIENCE OF BEING OFF COURSE WITH THE GPS AND IT EVEN SHOWED HIM IN MEXICO AT ONE TIME. HE VEHEMENTLY STATES THAT THE FAA SHOULD NOT EVEN CONSIDER DOING AWAY WITH THE VOR NAVAIDS SINCE THERE WOULD THEN BE NO BACKUP AT ALL.

Data retrieved from NASA's ASRS site as of July 2007 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.