Narrative:

I was working the low altitude arrival sector to den with 1 aircraft air carrier X. Air carrier was cleared for the profile descent which is a restriction to cross drako intersection between 17,000 and FL230. Air carrier was approximately 17 mi west of drako intersection at 17,000 (bottom of the profile window). He was also about 5 mi west of longs peak (14,255') in a 16,300' minimum instrument altitude area. I noticed air carrier's mode C readout of 167 (300' below his clearance). I called him and asked him to verify his altitude, he did not answer. I called again and he then reported he was descending out of 16,100' at this time longs peak was at his 12-1 O'clock and 2-3 mi. I gave air carrier instructions to climb immediately and informed him of his position to longs peak and the mia. The pilot responded with a rapid climb back up to 17,000. The lowest mode C readout I observed was 15,100 over longs peak. The profile descent after drako is a clearance to 13,000. I believe (but did not confirm) that the pilot programmed the aircraft to descend to 13,000 and did not monitor his position to drako.

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Original NASA ASRS Text

Title: ACR ON PROFILE DESCENT ARR DESCENDS BELOW MINIMUM INSTRUMENT ALT IN IMC CONDITIONS. CONTROLLED FLT TOWARD TERRAIN.

Narrative: I WAS WORKING THE LOW ALT ARR SECTOR TO DEN WITH 1 ACFT ACR X. ACR WAS CLRED FOR THE PROFILE DSCNT WHICH IS A RESTRICTION TO CROSS DRAKO INTXN BETWEEN 17,000 AND FL230. ACR WAS APPROX 17 MI W OF DRAKO INTXN AT 17,000 (BOTTOM OF THE PROFILE WINDOW). HE WAS ALSO ABOUT 5 MI W OF LONGS PEAK (14,255') IN A 16,300' MINIMUM INSTRUMENT ALT AREA. I NOTICED ACR'S MODE C READOUT OF 167 (300' BELOW HIS CLRNC). I CALLED HIM AND ASKED HIM TO VERIFY HIS ALT, HE DID NOT ANSWER. I CALLED AGAIN AND HE THEN REPORTED HE WAS DSNDING OUT OF 16,100' AT THIS TIME LONGS PEAK WAS AT HIS 12-1 O'CLOCK AND 2-3 MI. I GAVE ACR INSTRUCTIONS TO CLIMB IMMEDIATELY AND INFORMED HIM OF HIS POSITION TO LONGS PEAK AND THE MIA. THE PLT RESPONDED WITH A RAPID CLIMB BACK UP TO 17,000. THE LOWEST MODE C READOUT I OBSERVED WAS 15,100 OVER LONGS PEAK. THE PROFILE DSCNT AFTER DRAKO IS A CLRNC TO 13,000. I BELIEVE (BUT DID NOT CONFIRM) THAT THE PLT PROGRAMMED THE ACFT TO DSND TO 13,000 AND DID NOT MONITOR HIS POSITION TO DRAKO.

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.