Narrative:

This event was the classic error of a mis-set altimeter. The actual altimeter setting, due to a deep low that had created a storm (snow) in the middle atlantic states, was 29.31. The storm had passed earlier in the morning and WX conditions were fairly clear and cold. Normally a high pressure visual picture. At FL250 we were given a clearance to cross druzz at 11000 ft and 250 KTS with an altimeter setting of 29.31. This was the end of a 4 day trip on which I did not get good rest the previous 2 nights. When given the altimeter setting, I set 30.31 in the standby altimeter, as a reference for the setting as we passed through FL180. Descending through FL180 I set 30.31 in the captain's altimeter and called out '30.31' to complete the approach descent checklist. The copilot set 30.31. At 10200 ft, the center controller pointed out our altitude error and we climbed back to 11000 ft with the correct altimeter setting of 29.31. Prevention of this type of error can only be prevented by increased awareness of the possibility of oversights when alertness is compromised. I'll be sure to check center altimeter given with ATIS altimeter received before setting an altimeter reading in the future. Supplemental information from acn 295667: a check of the ATIS information that had been copied revealed that 29.31 was correct. This check is something that I normally do at 18000 ft when resetting altimeter. However, distracted by a flight attendant inquiring about connecting gates, I failed to xchk the setting. A contributing factor to the wrong setting was the quickly improving WX that had continued throughout the day - making 30.31 a plausible setting.

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Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT DURING DSCNT.

Narrative: THIS EVENT WAS THE CLASSIC ERROR OF A MIS-SET ALTIMETER. THE ACTUAL ALTIMETER SETTING, DUE TO A DEEP LOW THAT HAD CREATED A STORM (SNOW) IN THE MIDDLE ATLANTIC STATES, WAS 29.31. THE STORM HAD PASSED EARLIER IN THE MORNING AND WX CONDITIONS WERE FAIRLY CLR AND COLD. NORMALLY A HIGH PRESSURE VISUAL PICTURE. AT FL250 WE WERE GIVEN A CLRNC TO CROSS DRUZZ AT 11000 FT AND 250 KTS WITH AN ALTIMETER SETTING OF 29.31. THIS WAS THE END OF A 4 DAY TRIP ON WHICH I DID NOT GET GOOD REST THE PREVIOUS 2 NIGHTS. WHEN GIVEN THE ALTIMETER SETTING, I SET 30.31 IN THE STANDBY ALTIMETER, AS A REF FOR THE SETTING AS WE PASSED THROUGH FL180. DSNDING THROUGH FL180 I SET 30.31 IN THE CAPT'S ALTIMETER AND CALLED OUT '30.31' TO COMPLETE THE APCH DSCNT CHKLIST. THE COPLT SET 30.31. AT 10200 FT, THE CTR CTLR POINTED OUT OUR ALT ERROR AND WE CLBED BACK TO 11000 FT WITH THE CORRECT ALTIMETER SETTING OF 29.31. PREVENTION OF THIS TYPE OF ERROR CAN ONLY BE PREVENTED BY INCREASED AWARENESS OF THE POSSIBILITY OF OVERSIGHTS WHEN ALERTNESS IS COMPROMISED. I'LL BE SURE TO CHK CTR ALTIMETER GIVEN WITH ATIS ALTIMETER RECEIVED BEFORE SETTING AN ALTIMETER READING IN THE FUTURE. SUPPLEMENTAL INFO FROM ACN 295667: A CHK OF THE ATIS INFO THAT HAD BEEN COPIED REVEALED THAT 29.31 WAS CORRECT. THIS CHK IS SOMETHING THAT I NORMALLY DO AT 18000 FT WHEN RESETTING ALTIMETER. HOWEVER, DISTRACTED BY A FLT ATTENDANT INQUIRING ABOUT CONNECTING GATES, I FAILED TO XCHK THE SETTING. A CONTRIBUTING FACTOR TO THE WRONG SETTING WAS THE QUICKLY IMPROVING WX THAT HAD CONTINUED THROUGHOUT THE DAY - MAKING 30.31 A PLAUSIBLE SETTING.

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.