TRACK DEV.

Narrative

FOR LEARJET TRIP FROM PNE TO TNCM; FLT PLAN BY COMMERCIAL PROVIDER USING GPS AND DUAL VLF OMEGA LONG-RANGE NAV. ACFT WAS CLRED ALONG AIRWAY A300. NOTICING A DISCREPANCY ON THE GPS; WE TURNED TO THE VLF OMEGA FOR NAV. ON AIRWAY A300 TOWARDS LACKI INTXN; WE TUNED IN THE BERMUDA VOR; AND NOTICED THE BEARING AND DME WAS NOT IN TRACK WITH OUR POS AND WITH HOLMA INTXN. NEW YORK RADIO ASKED US TO CONTACT BERMUDA APCH. BERMUDA APCH ASKED FOR OUR POS. OUR POS DID NOT COINCIDE WITH THEIR POS OF US. WE ASKED THE CTLR FOR A NEW LATITUDE AND LONGITUDE POS TO REPROGRAM OUR VLF OMEGA. WE TURNED S TOWARDS HOLMA INTXN. APPROX 5 MINS ALONG THIS TRACK; THE CTLR ASKED FOR OUR POS. OUR POS AND THE CTLR'S LATITUDE AND LONGITUDE DID NOT COINCIDE. AGAIN; WE REPROGRAMMED THE VLF WITH NEW LATITUDE AND LONGITUDE FROM THE CTLR. ANOTHER CHK OF OUR POSITIONING WAS DONE WITHIN 5 MINS. THIS TIME OUR POSITIONING AND THE CTLR'S MATCHED. NOTICING WE WERE STILL E OF COURSE; BERMUDA APCH ISSUED A NEW RTE TO TNCM VIA A523. AT THIS TIME THE VLF NAV EQUIP SEEMED TO BE FUNCTIONING PROPERLY. BERMUDA APCH TURNED US BACK OVER TO NEW YORK RADIO. NO EVASIVE ACTION WAS REQUIRED ON THIS FLT. FACTORS CONTRIBUTING TO THIS SIT; WAS AN ERRONEOUS READING ON THE GPS AND INCONSISTENCY WITH THE VLF OMEGA LONG-RANGE NAV. I FEEL THIS SIT OCCURRED BECAUSE THE VLF DOES NOT RECEIVE ENOUGH USAGE ON DOMESTIC FLTS; WHILE CHKING ITS ACCURACY. TO PREVENT THIS FROM REOCCURRING; THE USE OF VLF ON DOMESTIC FLTS IS ADVISABLE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES A LEAR 35 IN AN AIR TAXI OP. HE HAS FLOWN ACFT WITH LORAN; OMEGA; AND GPS. THE GPS IS HIS FAVORITE; BY FAR. FOR SOME UNKNOWN REASON; THE GPS DID NOT WORK AS IT SHOULD THIS DAY. THERE IS A POSSIBILITY THAT THERE WAS A BAD DATA CARD IN USE THIS DAY; BUT IT WORKED CORRECTLY ON THE WAY BACK THE NEXT DAY. THE OMEGA WORKED PROPERLY AFTER THE SECOND RADAR FIX UPDATE FROM TXKF. THE RPTR HAS HAD NO PROBS WITH THE GPS IN ANY ACFT SINCE THAT TIME.