Narrative:

At the gate in stl while boarding; maintenance deferred the FMS; leaving us with short range (VOR) navigation only for our flight. We took off and proceeded on the blues 2 departure in short range nav. After making the turn over hilts; we noticed our CDI needle was acting erratic. Then ATC cleared us direct iiu. While navigating to iiu; both VOR 1 and 2 became completely unusable. Both CDI needles were going complete deflection over and over again in opposite directions. There were also numerous periods where the needle would lose the signal and a red X would appear. This whole time; we were getting a good identification when tuning the audio of the NAVAID. We were IMC for the entire climb and cruise; and alerted ATC we were having navigation issues and were going to troubleshoot. ATC gave us a heading and iiu when able. At this point; ATC asked an air carrier flight to attempt to tune in iiu; which they did and informed us and ATC they were getting a solid tune and course. During this entire time; we were getting closer to the iiu VOR and the situation did not get any better. As the flying pilot; I also attempted to tune the cvg VOR; and it gave the same completely unreliable guidance. At this point; we realized VOR 1 and 2 were unusable at all altitudes; multiple VORTAC; and any distance from the VOR. When the CDI began going full scale back and forth; the non-flying pilot called maintenance on arinc. Then the non-flying pilot was transferred to dispatch on arinc. We discussed going back to stl; but the field was IMC; with low ceilings; and we did not want to return to shoot an approach. After all the troubleshooting; communicating with ATC; and the company; we were past iiu and close to cvg. We checked the weather at cvg; which was 2 miles visibility; overcast skies at 1;400; and obviously shooting approaches. Dispatch relayed the destination weather; which was overcast at 8;000. Since there was an enormous weather pattern over the central us; it was determined that our planned destination was the best option because of the VMC conditions and the ability to shoot a visual approach. The first cause of this event was the FMS deferral at the gate by maintenance; limiting us to one form of navigation. This stemmed from a problem updating the database. The second cause was the failure in flight of both our VOR 1 and 2 equipment on board the airplane; leaving us with no navigational equipment in IMC conditions. Once we identified that we had an unreliable VOR 1 and 2; we first alerted ATC and got a heading. Then we contacted maintenance control via arinc to inform them. After that; we contacted dispatch to check the weather to find a suitable airport. Since stl was IMC; we chose not to return. We checked the nearest airport only to find it was also IMC from the same weather system. Our destination was IMC and forecast IMC; so we declared an emergency and got vectors for a visual approach. Upon picking up the field; we were cleared for the visual and no further incident occurred. Extra care needs to be taken to try to avoid deferring a navigation system and leaving only one system left on board. The FMS deferral should be a last resort option; not something to defer to get a flight out because one of the disks was having trouble downloading the database. The VOR navigational equipment should be looked at since it is rarely used as anything more then a backup to the FMS.

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Original NASA ASRS Text

Title: An ERJ145 with a deferred FMS lost both VOR receivers in flight which required ATC vectoring to their filed alternate because IMC weather prevented diversion to enroute airports.

Narrative: At the gate in STL while boarding; Maintenance deferred the FMS; leaving us with short range (VOR) navigation only for our flight. We took off and proceeded on the BLUES 2 Departure in short range nav. After making the turn over HILTS; we noticed our CDI needle was acting erratic. Then ATC cleared us direct IIU. While navigating to IIU; both VOR 1 and 2 became completely unusable. Both CDI needles were going complete deflection over and over again in opposite directions. There were also numerous periods where the needle would lose the signal and a red X would appear. This whole time; we were getting a good ID when tuning the audio of the NAVAID. We were IMC for the entire climb and cruise; and alerted ATC we were having navigation issues and were going to troubleshoot. ATC gave us a heading and IIU when able. At this point; ATC asked an Air Carrier flight to attempt to tune in IIU; which they did and informed us and ATC they were getting a solid tune and course. During this entire time; we were getting closer to the IIU VOR and the situation did not get any better. As the flying pilot; I also attempted to tune the CVG VOR; and it gave the same completely unreliable guidance. At this point; we realized VOR 1 and 2 were unusable at all altitudes; multiple VORTAC; and any distance from the VOR. When the CDI began going full scale back and forth; the non-flying pilot called Maintenance on ARINC. Then the non-flying pilot was transferred to Dispatch on ARINC. We discussed going back to STL; but the field was IMC; with low ceilings; and we did not want to return to shoot an approach. After all the troubleshooting; communicating with ATC; and the company; we were past IIU and close to CVG. We checked the weather at CVG; which was 2 miles visibility; overcast skies at 1;400; and obviously shooting approaches. Dispatch relayed the destination weather; which was overcast at 8;000. Since there was an enormous weather pattern over the central U.S.; it was determined that our planned destination was the best option because of the VMC conditions and the ability to shoot a visual approach. The first cause of this event was the FMS deferral at the gate by maintenance; limiting us to one form of navigation. This stemmed from a problem updating the database. The second cause was the failure in flight of both our VOR 1 and 2 equipment on board the airplane; leaving us with no navigational equipment in IMC conditions. Once we identified that we had an unreliable VOR 1 and 2; we first alerted ATC and got a heading. Then we contacted Maintenance Control via ARINC to inform them. After that; we contacted Dispatch to check the weather to find a suitable airport. Since STL was IMC; we chose not to return. We checked the nearest airport only to find it was also IMC from the same weather system. Our destination was IMC and forecast IMC; so we declared an emergency and got vectors for a visual approach. Upon picking up the field; we were cleared for the visual and no further incident occurred. Extra care needs to be taken to try to avoid deferring a navigation system and leaving only one system left on board. The FMS deferral should be a last resort option; not something to defer to get a flight out because one of the disks was having trouble downloading the database. The VOR navigational equipment should be looked at since it is rarely used as anything more then a backup to the FMS.

Data retrieved from NASA's ASRS site as of April 2012 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.