Narrative:

We received radar vectors to the final approach course for the VOR runway 24 at bridgeport, ct. The bdr VOR has no DME so we were using our aircraft navigation gear which is certified for IFR approach for distance information to establish the final approach fix. While our aircraft navigation showed us 3.8 mi from the VOR which was our missed approach point, the VOR needle reversed course indicating we were over the airport. We were breaking through the cloud deck and could see the airport behind us. The control tower asked us our intentions and we requested a special VFR clearance to the northwest to proceed to our company heliport which is 2 mi outside the kbdr air traffic area. We were unable to maintain SVFR to our heliport and had to request a special clearance back to the airport. After landing and thinking about what the control tower had said to us it seems that the tower thought we had crossed the airport and proceeded out of the control without requesting an SVFR clearance. Actually, we crossed the airport because we thought we were still 3.8 mi away. We had no indication from our navigation gear that the navigation abilities had been degraded to the extent that it was unsuitable for IFR navigation. We had been asked to keep up our speed on final so we shot by the airport at 140 KTS which contributed to the tower thinking we were proceeding without an SVFR clearance. We are presently investigating what the problem may be with our navigation system that caused it to lose accuracy. It may be helpful when making a VOR approach where there is no DME to xchk the final approach fix with a crossing radial to establish to final approach fix as a backup to aircraft navigation system.

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Original NASA ASRS Text

Title: CPR HELICOPTER MISSED APCH BECAUSE ONBOARD NAVIGATION SYSTEM WAS 4 NM IN ERROR.

Narrative: WE RECEIVED RADAR VECTORS TO THE FINAL APCH COURSE FOR THE VOR RWY 24 AT BRIDGEPORT, CT. THE BDR VOR HAS NO DME SO WE WERE USING OUR ACFT NAV GEAR WHICH IS CERTIFIED FOR IFR APCH FOR DISTANCE INFO TO ESTABLISH THE FINAL APCH FIX. WHILE OUR ACFT NAV SHOWED US 3.8 MI FROM THE VOR WHICH WAS OUR MISSED APCH POINT, THE VOR NEEDLE REVERSED COURSE INDICATING WE WERE OVER THE ARPT. WE WERE BREAKING THROUGH THE CLOUD DECK AND COULD SEE THE ARPT BEHIND US. THE CTL TWR ASKED US OUR INTENTIONS AND WE REQUESTED A SPECIAL VFR CLRNC TO THE NW TO PROCEED TO OUR COMPANY HELIPORT WHICH IS 2 MI OUTSIDE THE KBDR ATA. WE WERE UNABLE TO MAINTAIN SVFR TO OUR HELIPORT AND HAD TO REQUEST A SPECIAL CLRNC BACK TO THE ARPT. AFTER LNDG AND THINKING ABOUT WHAT THE CTL TWR HAD SAID TO US IT SEEMS THAT THE TWR THOUGHT WE HAD CROSSED THE ARPT AND PROCEEDED OUT OF THE CTL WITHOUT REQUESTING AN SVFR CLRNC. ACTUALLY, WE CROSSED THE ARPT BECAUSE WE THOUGHT WE WERE STILL 3.8 MI AWAY. WE HAD NO INDICATION FROM OUR NAV GEAR THAT THE NAVIGATION ABILITIES HAD BEEN DEGRADED TO THE EXTENT THAT IT WAS UNSUITABLE FOR IFR NAVIGATION. WE HAD BEEN ASKED TO KEEP UP OUR SPEED ON FINAL SO WE SHOT BY THE ARPT AT 140 KTS WHICH CONTRIBUTED TO THE TWR THINKING WE WERE PROCEEDING WITHOUT AN SVFR CLRNC. WE ARE PRESENTLY INVESTIGATING WHAT THE PROBLEM MAY BE WITH OUR NAV SYSTEM THAT CAUSED IT TO LOSE ACCURACY. IT MAY BE HELPFUL WHEN MAKING A VOR APCH WHERE THERE IS NO DME TO XCHK THE FINAL APCH FIX WITH A XING RADIAL TO ESTABLISH TO FINAL APCH FIX AS A BACKUP TO ACFT NAVIGATION SYSTEM.

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.