B727 CREW DSNDS BELOW ASSIGNED ALT ON APCH TO BIL AFTER RWY CHANGE. GPWS WARNING OCCURS AND CREW PERFORMS AN ESCAPE MANEUVER.

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DURING APCH TO RWY 10L AT BILLINGS; THE RWY WAS CHANGED TO RWY 28. THIS PLACED OUR ACFT HIGH AND FAST FOR THE APCH. IN AN EFFORT TO GET THE ACFT DOWN AND SLOWED; THE CAPT ASKED FOR A VECTOR; WHICH WAS RECEIVED. WE WERE THEN VECTORED BACK TO A DOG-LEG; 3 MILES OUTSIDE THE MARKER. THE ACFT WAS STILL HIGH AND WAS NOT CONFIGURED. WE WERE GIVEN A DSCNT TO 5300 FT AND A TURN TO INTERCEPT THE LOCALIZER. DURING THIS MANEUVER; THE FO; AN IOE STUDENT; LOST SITUATIONAL AWARENESS OF HIS DSCNT RATE AND THE FACT THAT HE HAD THE SPD BRAKES DEPLOYED. I INFORMED HIM THAT HE WAS ABOUT TO DSND BELOW 5300 FT. AS WE DSNDED THROUGH 5500 FT; THE CAPT TOOK THE AIRPLANE AND RECOVERED AT 5100 FT. AT THIS POINT; WE RECEIVED A GPWS 'WHOOP WHOOP TERRAIN' WARNING AND WERE FORCED TO EXECUTE AN ESCAPE MANEUVER. THIS RESULTED IN A CLB TO 7000' MSL. WE INFORMED APCH; WHO ASKED US TO STOP CLB AT 6000 FT MSL. WE WERE ALREADY NOSE HIGH PASSING 6600 FT AT THE TIME; WHICH WE COMMUNICATED TO APCH CTL. DUE TO OUR ALT AND AN IMPENDING CONFLICT WITH OTHER TFC; WE WERE TOLD TO TURN NORTH AND 'EXPEDITE' THE TURN. WE COMPLIED AND THEN WERE VECTORED BACK AROUND FOR ANOTHER; UNEVENTFUL APCH.