Narrative:

First officer flying thought clearance was to cross mayo intersection at 22000'. Center said to climb back to 24000', then 23000'. Actual clearance was 24000', expect 22000' at may intersection, per ATC. Supplemental information from acn 141751: we had been on duty for just under 10 hours and airborne for approximately 8 hours, 10 mins when the following incident occurred. I had been awake for 26+ hours. Pp/descent clrncs had been issued in a step-down manner. I anticipated the next crossing restriction to be FL220 at mayos and programmed it into the legs page of the FMC. Pp/as we descended through 25800', ZDC issued the following: 'your discretion to FL240, expect to cross mayos at FL220;' however, I anticipated and heard the following: 'your discretion to 240, cross mayos at 220.' very routine, however incorrect. Fatigue and anticipation had led me to hear what I wanted to hear. Pp/the captain working the radio read back the clearance as he had heard it, correctly. I once again heard what I wanted to hear: 'cross mayos at FL220.' having incorrectly heard 'cross mayos at 220,' I set 22000' in the altitude window on them cp. I then selected the vertical speed mode and reduced the rate of descent to 1000 FPM. The vertical speed mode provides altitude protection for the altitude you have selected in the altitude window only and does not interface with the FMC. Pp/the captain did not x-chk the altitude I had set in the altitude window and did not notice that I was operating in vertical speed mode. I did not xchk his FMC entry and thus had nothing in view to cause alarm. The international relief officer (international relief officer) was reading a magazine and gave us no input at all. He either didn't realize what was happening, or was completely out of the loop by reading. We had not said a work to each other since the clearance had been given. Pp/descending through 23200' ATC advised, 'stop your descent at FL240.' we did not response. At this point I disconnected the autoplt and started a climb back up to FL240. We assume equal blame for the incident, and surmised that (our trust in each other and the computer not to screw up) complacency (for lack of a better word), along with fatigue, led to all 3 of us operating in our own personal loop. Moral of the story: same old thing!! Stay in the loop!! And keep the communication flowing!! I'm not new to the FMC/MCP/CDU. I have 1900+ hours in aircraft with similar systems. Familiarity with the system was not a factor.

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Original NASA ASRS Text

Title: ALT DEVIATION.

Narrative: F/O FLYING THOUGHT CLRNC WAS TO CROSS MAYO INTXN AT 22000'. CENTER SAID TO CLB BACK TO 24000', THEN 23000'. ACTUAL CLRNC WAS 24000', EXPECT 22000' AT MAY INTXN, PER ATC. SUPPLEMENTAL INFO FROM ACN 141751: WE HAD BEEN ON DUTY FOR JUST UNDER 10 HRS AND AIRBORNE FOR APPROX 8 HRS, 10 MINS WHEN THE FOLLOWING INCIDENT OCCURRED. I HAD BEEN AWAKE FOR 26+ HRS. PP/DSCNT CLRNCS HAD BEEN ISSUED IN A STEP-DOWN MANNER. I ANTICIPATED THE NEXT XING RESTRICTION TO BE FL220 AT MAYOS AND PROGRAMMED IT INTO THE LEGS PAGE OF THE FMC. PP/AS WE DSNDED THROUGH 25800', ZDC ISSUED THE FOLLOWING: 'YOUR DISCRETION TO FL240, EXPECT TO CROSS MAYOS AT FL220;' HOWEVER, I ANTICIPATED AND HEARD THE FOLLOWING: 'YOUR DISCRETION TO 240, CROSS MAYOS AT 220.' VERY ROUTINE, HOWEVER INCORRECT. FATIGUE AND ANTICIPATION HAD LED ME TO HEAR WHAT I WANTED TO HEAR. PP/THE CAPT WORKING THE RADIO READ BACK THE CLRNC AS HE HAD HEARD IT, CORRECTLY. I ONCE AGAIN HEARD WHAT I WANTED TO HEAR: 'CROSS MAYOS AT FL220.' HAVING INCORRECTLY HEARD 'CROSS MAYOS AT 220,' I SET 22000' IN THE ALT WINDOW ON THEM CP. I THEN SELECTED THE VERT SPD MODE AND REDUCED THE RATE OF DSCNT TO 1000 FPM. THE VERT SPD MODE PROVIDES ALT PROTECTION FOR THE ALT YOU HAVE SELECTED IN THE ALT WINDOW ONLY AND DOES NOT INTERFACE WITH THE FMC. PP/THE CAPT DID NOT X-CHK THE ALT I HAD SET IN THE ALT WINDOW AND DID NOT NOTICE THAT I WAS OPERATING IN VERT SPD MODE. I DID NOT XCHK HIS FMC ENTRY AND THUS HAD NOTHING IN VIEW TO CAUSE ALARM. THE IRO (INTL RELIEF OFFICER) WAS READING A MAGAZINE AND GAVE US NO INPUT AT ALL. HE EITHER DIDN'T REALIZE WHAT WAS HAPPENING, OR WAS COMPLETELY OUT OF THE LOOP BY READING. WE HAD NOT SAID A WORK TO EACH OTHER SINCE THE CLRNC HAD BEEN GIVEN. PP/DSNDING THROUGH 23200' ATC ADVISED, 'STOP YOUR DSCNT AT FL240.' WE DID NOT RESPONSE. AT THIS POINT I DISCONNECTED THE AUTOPLT AND STARTED A CLB BACK UP TO FL240. WE ASSUME EQUAL BLAME FOR THE INCIDENT, AND SURMISED THAT (OUR TRUST IN EACH OTHER AND THE COMPUTER NOT TO SCREW UP) COMPLACENCY (FOR LACK OF A BETTER WORD), ALONG WITH FATIGUE, LED TO ALL 3 OF US OPERATING IN OUR OWN PERSONAL LOOP. MORAL OF THE STORY: SAME OLD THING!! STAY IN THE LOOP!! AND KEEP THE COM FLOWING!! I'M NOT NEW TO THE FMC/MCP/CDU. I HAVE 1900+ HRS IN ACFT WITH SIMILAR SYSTEMS. FAMILIARITY WITH THE SYS WAS NOT A FACTOR.

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.