Narrative:

While conducting a flight; we had to divert and use captain's emergency authority/authorized to land. We flew to ZZZ without any irregularities during the en route phase. We shot a localizer approach to runway. We initially saw the runway and proceeded to land. The runway became obscured by clouds and we executed a missed approach. We requested an ILS to runway to obtain a lower decision altitude. While executing the ILS approach and the localizer display started to deviation left and right of center. The aircraft was coupled with the autoplt engaged. The aircraft started a series of gradually increasing turns left and right trying to obtain appropriate course guidance. I disengaged the autoplt and proceeded to hand fly the approach. I was unable to regain a suitable track to the runway and was not configured appropriately for our phase of approach. I elected to execute another missed approach procedure. We asked the tower to make sure his localizer was showing a good signal. The tower indicated he had reset the localizer and it was operating. We elected to execute another ILS approach. We briefed each other that if localizer integrity was again in question below 1000 ft we would execute another missed approach and divert. On the second ILS approach; the same series of events transpired with the localizer shifting right and left of center. We executed a missed approach at around 1000 ft and diverted. At ZZZ thunderstorms in the area made an ILS approach a poor choice; so we chose a VOR approach to runway 36. When established on the inbound course and having been cleared for the approach and told to switch to CTAF; the VOR course started to vary left and right of course with the autoplt following the course. I once again disconnected the autoplt. At this point the left fuel tank quantity was showing amber. I determined we were in an emergency situation with an unreliable navigation system; low fuel and thunderstorms in the area. I exercised captain's emergency authority/authorized and switched my primary navigation from the VOR to the FMS VOR approach. We landed from this approach.

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Original NASA ASRS Text

Title: E140 FLT CREW EXPERIENCES REPEATING UNRELIABILITY OF LOC-VOR COURSE AT DEST AND ALTERNATE. EXERCISE EMER AUTH TO FLY VOR APCH VIA FMS MAP DISPLAY WITHOUT RAW DATA INFO.

Narrative: WHILE CONDUCTING A FLT; WE HAD TO DIVERT AND USE CAPT'S EMER AUTH TO LAND. WE FLEW TO ZZZ WITHOUT ANY IRREGULARITIES DURING THE ENRTE PHASE. WE SHOT A LOC APCH TO RWY. WE INITIALLY SAW THE RWY AND PROCEEDED TO LAND. THE RWY BECAME OBSCURED BY CLOUDS AND WE EXECUTED A MISSED APCH. WE REQUESTED AN ILS TO RWY TO OBTAIN A LOWER DECISION ALT. WHILE EXECUTING THE ILS APCH AND THE LOC DISPLAY STARTED TO DEV L AND R OF CTR. THE ACFT WAS COUPLED WITH THE AUTOPLT ENGAGED. THE ACFT STARTED A SERIES OF GRADUALLY INCREASING TURNS L AND R TRYING TO OBTAIN APPROPRIATE COURSE GUIDANCE. I DISENGAGED THE AUTOPLT AND PROCEEDED TO HAND FLY THE APCH. I WAS UNABLE TO REGAIN A SUITABLE TRACK TO THE RWY AND WAS NOT CONFIGURED APPROPRIATELY FOR OUR PHASE OF APCH. I ELECTED TO EXECUTE ANOTHER MISSED APCH PROC. WE ASKED THE TWR TO MAKE SURE HIS LOC WAS SHOWING A GOOD SIGNAL. THE TWR INDICATED HE HAD RESET THE LOC AND IT WAS OPERATING. WE ELECTED TO EXECUTE ANOTHER ILS APCH. WE BRIEFED EACH OTHER THAT IF LOC INTEGRITY WAS AGAIN IN QUESTION BELOW 1000 FT WE WOULD EXECUTE ANOTHER MISSED APCH AND DIVERT. ON THE SECOND ILS APCH; THE SAME SERIES OF EVENTS TRANSPIRED WITH THE LOC SHIFTING R AND L OF CTR. WE EXECUTED A MISSED APCH AT AROUND 1000 FT AND DIVERTED. AT ZZZ TSTMS IN THE AREA MADE AN ILS APCH A POOR CHOICE; SO WE CHOSE A VOR APCH TO RWY 36. WHEN ESTABLISHED ON THE INBOUND COURSE AND HAVING BEEN CLRED FOR THE APCH AND TOLD TO SWITCH TO CTAF; THE VOR COURSE STARTED TO VARY L AND R OF COURSE WITH THE AUTOPLT FOLLOWING THE COURSE. I ONCE AGAIN DISCONNECTED THE AUTOPLT. AT THIS POINT THE L FUEL TANK QUANTITY WAS SHOWING AMBER. I DETERMINED WE WERE IN AN EMER SITUATION WITH AN UNRELIABLE NAV SYS; LOW FUEL AND TSTMS IN THE AREA. I EXERCISED CAPT'S EMER AUTH AND SWITCHED MY PRIMARY NAV FROM THE VOR TO THE FMS VOR APCH. WE LANDED FROM THIS APCH.

Data retrieved from NASA's ASRS site as of January 2009 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.