Narrative:

We were on approach to abe in level flight at 2800' MSL in IMC conditions. We were being vectored to the back course localizer 24 approach at abe. We were heading approximately 190 degrees. Suddenly the GPWS sounded a terrain alert. My copilot immediately initiated a climb as I declared an emergency to ATC to alert them to our climb out of the assigned altitude. The terrain warning stopped somewhere between 3200-3500' MSL. We leveled the aircraft at 4000' MSL, still in IMC. We then continued into abe to a normal landing. There was not any traffic conflict. I talked to the TRACON facility after I got on the ground and they confirmed I was at the minimum vectoring altitude of 2800' MSL. They also said I was very close to an adjacent sector that had an MVA of 3300' MSL. They mentioned that one of the reasons the MVA was 3300' MSL in the adjacent sector was that they had had terrain alerts in the sector. I do not believe there was any problem with our GPWS (it had self tested properly). I believe we had a valid alert due to excessive closure rate with rising terrain (there is a prominent ridge in that area). I think to preclude further terrain alerts which could cause traffic conflicts in the future, the MVA of 2800' MSL should be considered for revision upward.

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Original NASA ASRS Text

Title: GPWS ACTIVATED DURING RADAR VECTOR TO BACK COURSE APCH TO ABE. ACFT WAS AT THE CORRECT VECTOR ALT AS CONFIRMED BY ABE TRACON.

Narrative: WE WERE ON APCH TO ABE IN LEVEL FLT AT 2800' MSL IN IMC CONDITIONS. WE WERE BEING VECTORED TO THE BACK COURSE LOC 24 APCH AT ABE. WE WERE HDG APPROX 190 DEGS. SUDDENLY THE GPWS SOUNDED A TERRAIN ALERT. MY COPLT IMMEDIATELY INITIATED A CLB AS I DECLARED AN EMER TO ATC TO ALERT THEM TO OUR CLBOUT OF THE ASSIGNED ALT. THE TERRAIN WARNING STOPPED SOMEWHERE BTWN 3200-3500' MSL. WE LEVELED THE ACFT AT 4000' MSL, STILL IN IMC. WE THEN CONTINUED INTO ABE TO A NORMAL LNDG. THERE WAS NOT ANY TFC CONFLICT. I TALKED TO THE TRACON FAC AFTER I GOT ON THE GND AND THEY CONFIRMED I WAS AT THE MINIMUM VECTORING ALT OF 2800' MSL. THEY ALSO SAID I WAS VERY CLOSE TO AN ADJACENT SECTOR THAT HAD AN MVA OF 3300' MSL. THEY MENTIONED THAT ONE OF THE REASONS THE MVA WAS 3300' MSL IN THE ADJACENT SECTOR WAS THAT THEY HAD HAD TERRAIN ALERTS IN THE SECTOR. I DO NOT BELIEVE THERE WAS ANY PROB WITH OUR GPWS (IT HAD SELF TESTED PROPERLY). I BELIEVE WE HAD A VALID ALERT DUE TO EXCESSIVE CLOSURE RATE WITH RISING TERRAIN (THERE IS A PROMINENT RIDGE IN THAT AREA). I THINK TO PRECLUDE FURTHER TERRAIN ALERTS WHICH COULD CAUSE TFC CONFLICTS IN THE FUTURE, THE MVA OF 2800' MSL SHOULD BE CONSIDERED FOR REVISION UPWARD.

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.