Narrative:

We were completing our 6TH day of flying. Our trip took us from ord-lhr-lax-lhr-ord, total time was about 40 hours and 20 mins. We were descending across lake michigan for our approach into O'hare. Other air carrier flts from europe were arriving at the same time with call signs like ay and by, ours was cy. The frequency was crowded and there had already been a few missed calls and minor confusions already related to call signs. ATC cleared us to descend below FL180, gave us a heading to intercept an airway, cross an intersection that was not in our FMC map display, at a specific altitude, and to change our speed, followed by a qnh altimeter setting. I responded to the bulk of the clearance as I was putting the crossing fix manually into the database. I noticed that the altimeter setting was only 2 hundredths off the setting that the io had prepared on our changeover paperwork and 'rogered' it. As the captain leveled at what we thought was 10000 ft, ATC hollered at us that we were only cleared to 10000. I responded that we there, and to confirm the altimeter. He said 29.46. As the captain dialed it in, it of course now put us at about 9600 ft, 400 low! Which then made the altimeter alert system in the cockpit go off and give red warning lights and alarms. This of course clued in the FAA inspector that was riding on the jumpseat and aroused his attention (oh yeah, had I mentioned that we had an air carrier inspector on board for the 11 hour leg back home)? The captain then disconnected the autoplt and made a correction back up. Our TCASII system did not put any aircraft within 12 mi of our position and did not go off. We at abc airlines use a 3 altimeter procedure, so that the captain and first officer have theirs set to QFE and it will read 0 at touchdown. While the 3RD one is set to qnh and will read field elevation. The problem began with the changeover paperwork. With our ACARS model for data link, we have to enter the altimeter setting in order to get the conversion number (for the captain and first officer's altimeters) and gate arrival information. Unbeknownst to us the initial officer had the WX from the latest ord sa and ft uplink, he interpreted the wind /3016/ as the altimeter setting, (instead of transcribing the ATIS directly on to our landing information paperwork) entered that number into ACARS and came up with a conversion factor of 29.44. This, both the captain and I accepted as it was close to the number ATC had given us and that we wanted to hear. Once on the ground we debriefed the fed, who was not familiar with either the aircraft or our altimeter procedures. He seemed satisfied and did not give the impression that it would go any further. There was no demand from any controller for a landline conversation. The contributing factors? Fatigue, fatigue, fatigue, both mental and physical. A long and involved clearance, and radio congestion. Also, I will from now on change my altimeter directly from ATC as we are cleared through the transition altitude.

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Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT.

Narrative: WE WERE COMPLETING OUR 6TH DAY OF FLYING. OUR TRIP TOOK US FROM ORD-LHR-LAX-LHR-ORD, TOTAL TIME WAS ABOUT 40 HRS AND 20 MINS. WE WERE DSNDING ACROSS LAKE MICHIGAN FOR OUR APCH INTO O'HARE. OTHER ACR FLTS FROM EUROPE WERE ARRIVING AT THE SAME TIME WITH CALL SIGNS LIKE AY AND BY, OURS WAS CY. THE FREQ WAS CROWDED AND THERE HAD ALREADY BEEN A FEW MISSED CALLS AND MINOR CONFUSIONS ALREADY RELATED TO CALL SIGNS. ATC CLRED US TO DSND BELOW FL180, GAVE US A HDG TO INTERCEPT AN AIRWAY, CROSS AN INTXN THAT WAS NOT IN OUR FMC MAP DISPLAY, AT A SPECIFIC ALT, AND TO CHANGE OUR SPD, FOLLOWED BY A QNH ALTIMETER SETTING. I RESPONDED TO THE BULK OF THE CLRNC AS I WAS PUTTING THE XING FIX MANUALLY INTO THE DATABASE. I NOTICED THAT THE ALTIMETER SETTING WAS ONLY 2 HUNDREDTHS OFF THE SETTING THAT THE IO HAD PREPARED ON OUR CHANGEOVER PAPERWORK AND 'ROGERED' IT. AS THE CAPT LEVELED AT WHAT WE THOUGHT WAS 10000 FT, ATC HOLLERED AT US THAT WE WERE ONLY CLRED TO 10000. I RESPONDED THAT WE THERE, AND TO CONFIRM THE ALTIMETER. HE SAID 29.46. AS THE CAPT DIALED IT IN, IT OF COURSE NOW PUT US AT ABOUT 9600 FT, 400 LOW! WHICH THEN MADE THE ALTIMETER ALERT SYS IN THE COCKPIT GO OFF AND GIVE RED WARNING LIGHTS AND ALARMS. THIS OF COURSE CLUED IN THE FAA INSPECTOR THAT WAS RIDING ON THE JUMPSEAT AND AROUSED HIS ATTN (OH YEAH, HAD I MENTIONED THAT WE HAD AN ACR INSPECTOR ON BOARD FOR THE 11 HR LEG BACK HOME)? THE CAPT THEN DISCONNECTED THE AUTOPLT AND MADE A CORRECTION BACK UP. OUR TCASII SYS DID NOT PUT ANY ACFT WITHIN 12 MI OF OUR POS AND DID NOT GO OFF. WE AT ABC AIRLINES USE A 3 ALTIMETER PROC, SO THAT THE CAPT AND FO HAVE THEIRS SET TO QFE AND IT WILL READ 0 AT TOUCHDOWN. WHILE THE 3RD ONE IS SET TO QNH AND WILL READ FIELD ELEVATION. THE PROBLEM BEGAN WITH THE CHANGEOVER PAPERWORK. WITH OUR ACARS MODEL FOR DATA LINK, WE HAVE TO ENTER THE ALTIMETER SETTING IN ORDER TO GET THE CONVERSION NUMBER (FOR THE CAPT AND FO'S ALTIMETERS) AND GATE ARR INFO. UNBEKNOWNST TO US THE INITIAL OFFICER HAD THE WX FROM THE LATEST ORD SA AND FT UPLINK, HE INTERPRETED THE WIND /3016/ AS THE ALTIMETER SETTING, (INSTEAD OF TRANSCRIBING THE ATIS DIRECTLY ON TO OUR LNDG INFO PAPERWORK) ENTERED THAT NUMBER INTO ACARS AND CAME UP WITH A CONVERSION FACTOR OF 29.44. THIS, BOTH THE CAPT AND I ACCEPTED AS IT WAS CLOSE TO THE NUMBER ATC HAD GIVEN US AND THAT WE WANTED TO HEAR. ONCE ON THE GND WE DEBRIEFED THE FED, WHO WAS NOT FAMILIAR WITH EITHER THE ACFT OR OUR ALTIMETER PROCS. HE SEEMED SATISFIED AND DID NOT GIVE THE IMPRESSION THAT IT WOULD GO ANY FURTHER. THERE WAS NO DEMAND FROM ANY CTLR FOR A LANDLINE CONVERSATION. THE CONTRIBUTING FACTORS? FATIGUE, FATIGUE, FATIGUE, BOTH MENTAL AND PHYSICAL. A LONG AND INVOLVED CLRNC, AND RADIO CONGESTION. ALSO, I WILL FROM NOW ON CHANGE MY ALTIMETER DIRECTLY FROM ATC AS WE ARE CLRED THROUGH THE TRANSITION ALT.

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.