Narrative:

During vectors for approach to anc ILS runway 6R, ATC gave altimeter setting 29.87 (sounded like and was read back). We had 28.97 set but, thinking we had copied wrong data in ATIS report, we changed to 29.87. Approach controller asked our altitude and we verified it was 2000 ft (cleared to 1600 ft). He stated his readout was more than 300 ft different than our reported altitude and advised altitude 'low 28.87' and to turn off our altitude encoder as it was in error. We crosschecked the radar altitude and reset the altimeters to this setting and adjusted our altitude. Rest of flight was normal.

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Original NASA ASRS Text

Title: AN ACR MLG GOT BELOW ITS ASSIGNED ALT WHEN IT MISUNDERSTOOD THE VERY LOW ALTIMETER SETTING.

Narrative: DURING VECTORS FOR APCH TO ANC ILS RWY 6R, ATC GAVE ALTIMETER SETTING 29.87 (SOUNDED LIKE AND WAS READ BACK). WE HAD 28.97 SET BUT, THINKING WE HAD COPIED WRONG DATA IN ATIS RPT, WE CHANGED TO 29.87. APCH CTLR ASKED OUR ALT AND WE VERIFIED IT WAS 2000 FT (CLRED TO 1600 FT). HE STATED HIS READOUT WAS MORE THAN 300 FT DIFFERENT THAN OUR RPTED ALT AND ADVISED ALT 'LOW 28.87' AND TO TURN OFF OUR ALT ENCODER AS IT WAS IN ERROR. WE XCHKED THE RADAR ALT AND RESET THE ALTIMETERS TO THIS SETTING AND ADJUSTED OUR ALT. REST OF FLT WAS NORMAL.

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