Narrative:

On a flight into cpr; we were cleared direct cpr about 30 mi northwest of denver. Climb and cruise were uneventful. Approximately 75 mi ssw of casper we received clearance to descend from FL230 to 11000 ft pilot's discretion. We configured the aircraft as usual while in a gradual descent down to 11000 ft MSL. Approximately 35 mi away we decided that we hadn't heard any traffic on the frequency for a while; and called ATC. A different ATC controller answered the radio call; with '(flight number) uh...ok; descend and maintain 8000 ft; casper airport 12 O'clock position; 35 mi; go ahead with request.' the captain (PNF) responded 'descend to 8000 ft; airport not in sight; just checking to see if you are still there; it's good to hear you.' 'it's good to be heard' was ATC's response. When we completed the in-range checklist; we discussed the terrain and turned on the egpws terrain map. Approximately 10500 ft we entered a cloud and IMC conditions. I am not sure of the exact altitude we descended to; but I believe that it was not ever less than 9000 ft MSL. Shortly after entering the cloud; maybe 45 seconds; we received our first egpws warning 'caution; obstacle; caution; obstacle.' as soon as I heard this warning; I disengaged the autoplt; added power; and arrested the descent. Very shortly after we received another egpws warning of 'climb; climb.' I increased power and began a smooth climb; and referenced the terrain map which showed a solid yellow DOT ahead and to the right. After beginning a climb; the third egpws warning sounded 'climb now! Climb now!' I immediately increased to maximum power and entered a 20 degree nose-up climb of more than 4500 FPM. As soon as we leveled off around 11500 ft; center called us and said '(flight number) casper airport 12 O'clock position; 23 mi.' PNF responded 'center; we just received a GPWS climb; verify altimeter 29.57.' ATC: '(flight number) casper altimeter 29.59.' the captain then again mentioned the climb; and questioned the previously assigned altitude of 8000 ft. Center responded 'that's correct (flight number) my lowest MVA is 8000 ft.' from this point; we continued the flight with a visual approach and landed without incident. After landing; we discussed the situation; referencing our charts and our knowledge of the area. We believed that we had been assigned an unsafe altitude by ZDV; and called the center supervisor to report the incident and get more information to figure out what happened. It is my belief that we were in fact issued a descent clearance to 8000 ft around 35 mi sse of casper. It is my understanding that the minimum safe vectoring altitude is around 10000 ft MSL. The mountain that triggered the egpws alert is over 8000 ft MSL; with radio towers on top extending around 8450 ft. I believe that if we had responded any differently; or if the egpws had failed to issue the warnings it did; this situation could have turned out very differently.

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Original NASA ASRS Text

Title: AN ACR ACFT GIVEN AN ATC DESCENT TO 8000 FT RECEIVED AN EGPWS 'CAUTION TERRAIN;' THEN A 'CLIMB;' THEN A 'CLIMB NOW' WARNING ABOUT 25 NM SW OF CPR AT 9000 FT.

Narrative: ON A FLT INTO CPR; WE WERE CLRED DIRECT CPR ABOUT 30 MI NW OF DENVER. CLB AND CRUISE WERE UNEVENTFUL. APPROX 75 MI SSW OF CASPER WE RECEIVED CLRNC TO DSND FROM FL230 TO 11000 FT PLT'S DISCRETION. WE CONFIGURED THE ACFT AS USUAL WHILE IN A GRADUAL DSCNT DOWN TO 11000 FT MSL. APPROX 35 MI AWAY WE DECIDED THAT WE HADN'T HEARD ANY TFC ON THE FREQ FOR A WHILE; AND CALLED ATC. A DIFFERENT ATC CTLR ANSWERED THE RADIO CALL; WITH '(FLT NUMBER) UH...OK; DSND AND MAINTAIN 8000 FT; CASPER ARPT 12 O'CLOCK POS; 35 MI; GO AHEAD WITH REQUEST.' THE CAPT (PNF) RESPONDED 'DSND TO 8000 FT; ARPT NOT IN SIGHT; JUST CHKING TO SEE IF YOU ARE STILL THERE; IT'S GOOD TO HEAR YOU.' 'IT'S GOOD TO BE HEARD' WAS ATC'S RESPONSE. WHEN WE COMPLETED THE IN-RANGE CHKLIST; WE DISCUSSED THE TERRAIN AND TURNED ON THE EGPWS TERRAIN MAP. APPROX 10500 FT WE ENTERED A CLOUD AND IMC CONDITIONS. I AM NOT SURE OF THE EXACT ALT WE DSNDED TO; BUT I BELIEVE THAT IT WAS NOT EVER LESS THAN 9000 FT MSL. SHORTLY AFTER ENTERING THE CLOUD; MAYBE 45 SECONDS; WE RECEIVED OUR FIRST EGPWS WARNING 'CAUTION; OBSTACLE; CAUTION; OBSTACLE.' AS SOON AS I HEARD THIS WARNING; I DISENGAGED THE AUTOPLT; ADDED PWR; AND ARRESTED THE DSCNT. VERY SHORTLY AFTER WE RECEIVED ANOTHER EGPWS WARNING OF 'CLB; CLB.' I INCREASED PWR AND BEGAN A SMOOTH CLB; AND REFED THE TERRAIN MAP WHICH SHOWED A SOLID YELLOW DOT AHEAD AND TO THE R. AFTER BEGINNING A CLB; THE THIRD EGPWS WARNING SOUNDED 'CLB NOW! CLB NOW!' I IMMEDIATELY INCREASED TO MAX PWR AND ENTERED A 20 DEG NOSE-UP CLB OF MORE THAN 4500 FPM. AS SOON AS WE LEVELED OFF AROUND 11500 FT; CTR CALLED US AND SAID '(FLT NUMBER) CASPER ARPT 12 O'CLOCK POS; 23 MI.' PNF RESPONDED 'CTR; WE JUST RECEIVED A GPWS CLB; VERIFY ALTIMETER 29.57.' ATC: '(FLT NUMBER) CASPER ALTIMETER 29.59.' THE CAPT THEN AGAIN MENTIONED THE CLB; AND QUESTIONED THE PREVIOUSLY ASSIGNED ALT OF 8000 FT. CTR RESPONDED 'THAT'S CORRECT (FLT NUMBER) MY LOWEST MVA IS 8000 FT.' FROM THIS POINT; WE CONTINUED THE FLT WITH A VISUAL APCH AND LANDED WITHOUT INCIDENT. AFTER LNDG; WE DISCUSSED THE SITUATION; REFING OUR CHARTS AND OUR KNOWLEDGE OF THE AREA. WE BELIEVED THAT WE HAD BEEN ASSIGNED AN UNSAFE ALT BY ZDV; AND CALLED THE CTR SUPVR TO RPT THE INCIDENT AND GET MORE INFO TO FIGURE OUT WHAT HAPPENED. IT IS MY BELIEF THAT WE WERE IN FACT ISSUED A DSCNT CLRNC TO 8000 FT AROUND 35 MI SSE OF CASPER. IT IS MY UNDERSTANDING THAT THE MINIMUM SAFE VECTORING ALT IS AROUND 10000 FT MSL. THE MOUNTAIN THAT TRIGGERED THE EGPWS ALERT IS OVER 8000 FT MSL; WITH RADIO TWRS ON TOP EXTENDING AROUND 8450 FT. I BELIEVE THAT IF WE HAD RESPONDED ANY DIFFERENTLY; OR IF THE EGPWS HAD FAILED TO ISSUE THE WARNINGS IT DID; THIS SITUATION COULD HAVE TURNED OUT VERY DIFFERENTLY.

Data retrieved from NASA's ASRS site as of May 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.