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.