Narrative:

[Inbound to] mfr; we received two terrain warnings after we were cleared for the ILS runway 14. We were inbound from the south and vectored to the west over high terrain; which was a normal path for runway 14. The first terrain warning occurred at 5;300 feet during vectors through the localizer. We were on a turn to 170 degrees to intercept the localizer; approximately 3 miles from amase. The course was alive and we heard the 'terrain terrain' warning. The pilot flying initiated a climb and continued to track the localizer. As we passed 6;000 feet and climbing; we heard the second 'terrain' warning. The pilot flying expedited his climb to 8;000 feet. I told cascade approach that we were going missed and responding to a terrain warning. At that point; ATC gave us a new heading and told us to maintain 9;000 feet. Once at 9;000 I checked all three altimeters: 29.89; which was correct. Neither of us could determine what went wrong since we were within 1 dot of the localizer and above cascade approach's minimum vectoring altitude during each of the warnings.we elected to try the ILS again. The bases near the airport were 4;000 feet and we both felt the terrain warnings were an aberration. Cascade approach vectored us on the eastern side of the airport for a long left downwind for the ILS to runway 14. From that point; everything proceeded normally.we were in IMC getting vectored by cascade approach at 5;300 feet. This was an altitude that I thought was above cascade's minimum vectoring altitude. Also; this altitude has worked in the past. So; I cannot say if there is an issue with the aircraft's terrain database or a problem with the vectoring by cascade. I am not sure if there is a solution other than make mfr a VFR only airport for part 121 operators until this issue is resolved.

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Original NASA ASRS Text

Title: Air carrier Check Airman reported receiving a GPWS terrain alert on approach to MFR in IFR conditions.

Narrative: [Inbound to] MFR; we received two terrain warnings after we were cleared for the ILS Runway 14. We were inbound from the south and vectored to the west over high terrain; which was a normal path for Runway 14. The first terrain warning occurred at 5;300 feet during vectors through the localizer. We were on a turn to 170 degrees to intercept the localizer; approximately 3 miles from AMASE. The course was alive and we heard the 'TERRAIN TERRAIN' warning. The pilot flying initiated a climb and continued to track the localizer. As we passed 6;000 feet and climbing; we heard the second 'TERRAIN' warning. The pilot flying expedited his climb to 8;000 feet. I told Cascade Approach that we were going missed and responding to a Terrain Warning. At that point; ATC gave us a new heading and told us to maintain 9;000 feet. Once at 9;000 I checked all three altimeters: 29.89; which was correct. Neither of us could determine what went wrong since we were within 1 dot of the localizer and above Cascade Approach's minimum vectoring altitude during each of the warnings.We elected to try the ILS again. The bases near the airport were 4;000 feet and we both felt the terrain warnings were an aberration. Cascade Approach vectored us on the eastern side of the airport for a long left downwind for the ILS to Runway 14. From that point; everything proceeded normally.We were in IMC getting vectored by Cascade Approach at 5;300 feet. This was an altitude that I thought was above Cascade's minimum vectoring altitude. Also; this altitude has worked in the past. So; I cannot say if there is an issue with the aircraft's terrain database or a problem with the vectoring by Cascade. I am not sure if there is a solution other than make MFR a VFR only airport for Part 121 operators until this issue is resolved.

Data retrieved from NASA's ASRS site 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.