Narrative:

I departed hnl in an light transport eastbound for oak on R465 (charlie track). After takeoff we proceeded normally. My GNS concurred with ATC's gndspd readout, as well as my position over cluts, my first chkpoint. At approximately 130 degrees west 2 degrees before costs, I was in clouds skimming the top of a cloud layer, IFR. My radar had been picking up a rainshower 12 O'clock and closing (50 mi initially). I radioed sfo that I would like to deviate north of course but coyle not get a response from oceanic, I tried twice the WX now showed 15 mi ahead. I decided to turn north to avoid this WX. There was a SIGMET out in my area for isolated thunderstorms and severe turbulence. As I initiated my turn my ground 'D-right' which means bad or inappropriate signal reception it remained in 'D-right' for approximately 14-16 mins. After clearing I resumed navigation according to my computer flight plan as well as my GNS which now returned to VLF on good signal. However, upon reaching clukk and N360500 west 1245000 an oak controller radar idented me 23 mi off course northwest of clukk. I told him I was unaware I was that far off course, but told him how I believed it happened and where. I believe if I could have reached oceanic control earlier and had stayed farther away from the WX my ground would not have 'D-right' and would have been more accurate. Thunderstorms can cause faulty GNS readouts. So, I believe turning sooner would have kept my GNS in a good navigation signal lock. I changed my destination to sjc and landed there instead of oak. As far as I was informed, there were no other aircraft in my area at the time. We are an air taxi operator but were operating part 91 at the time.

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Original NASA ASRS Text

Title: ATX LTT DEVIATION FROM CLRNC ROUTE AFTER ENCOUNTER WITH ENROUTE WX TSTM ACTIVITY.

Narrative: I DEPARTED HNL IN AN LTT EBND FOR OAK ON R465 (CHARLIE TRACK). AFTER TKOF WE PROCEEDED NORMALLY. MY GNS CONCURRED WITH ATC'S GNDSPD READOUT, AS WELL AS MY POS OVER CLUTS, MY FIRST CHKPOINT. AT APPROX 130 DEGS W 2 DEGS BEFORE COSTS, I WAS IN CLOUDS SKIMMING THE TOP OF A CLOUD LAYER, IFR. MY RADAR HAD BEEN PICKING UP A RAINSHOWER 12 O'CLOCK AND CLOSING (50 MI INITIALLY). I RADIOED SFO THAT I WOULD LIKE TO DEVIATE N OF COURSE BUT COYLE NOT GET A RESPONSE FROM OCEANIC, I TRIED TWICE THE WX NOW SHOWED 15 MI AHEAD. I DECIDED TO TURN N TO AVOID THIS WX. THERE WAS A SIGMET OUT IN MY AREA FOR ISOLATED TSTMS AND SEVERE TURB. AS I INITIATED MY TURN MY GND 'D-R' WHICH MEANS BAD OR INAPPROPRIATE SIGNAL RECEPTION IT REMAINED IN 'D-R' FOR APPROX 14-16 MINS. AFTER CLRING I RESUMED NAV ACCORDING TO MY COMPUTER FLT PLAN AS WELL AS MY GNS WHICH NOW RETURNED TO VLF ON GOOD SIGNAL. HOWEVER, UPON REACHING CLUKK AND N360500 W 1245000 AN OAK CTLR RADAR IDENTED ME 23 MI OFF COURSE NW OF CLUKK. I TOLD HIM I WAS UNAWARE I WAS THAT FAR OFF COURSE, BUT TOLD HIM HOW I BELIEVED IT HAPPENED AND WHERE. I BELIEVE IF I COULD HAVE REACHED OCEANIC CTL EARLIER AND HAD STAYED FARTHER AWAY FROM THE WX MY GND WOULD NOT HAVE 'D-R' AND WOULD HAVE BEEN MORE ACCURATE. TSTMS CAN CAUSE FAULTY GNS READOUTS. SO, I BELIEVE TURNING SOONER WOULD HAVE KEPT MY GNS IN A GOOD NAV SIGNAL LOCK. I CHANGED MY DEST TO SJC AND LANDED THERE INSTEAD OF OAK. AS FAR AS I WAS INFORMED, THERE WERE NO OTHER ACFT IN MY AREA AT THE TIME. WE ARE AN AIR TAXI OPERATOR BUT WERE OPERATING PART 91 AT THE TIME.

Data retrieved from NASA's ASRS site as of August 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.