Narrative:

We were given clearance to cross cofax at FL250 (we were at FL310 at the time). I was the PF. I programmed cofax at FL250 into the FMC and verified that I was on VNAV. A few mins later the captain stated he was going to go to the bathroom and got up. Just as he started out the cockpit door, I looked down and realized we were 1 mi from cofax. For whatever reason, the FMC/autoplt did not start the descent (still was annunciating VNAV) and I failed to back up the machine with basic airmanship. I immediately started down manually, notified ATC that I was starting out of FL310 at this time and apologized for missing the crossing restr. He said no problem, descend and maintain FL250, and contact new york on 132.2. Upon contact, they cleared us for direct lrp and a further descent with no crossing restrs. Contributing factors: 1) we had earlier been slowed down by ATC to 250 KTS which I programmed into the FMC. Then when we were given normal speed, I couldn't get it out. Captain said look at cruise descent page -- there it was. I took it out, put back economy cruise descent and thought everything was ok. I think, in retrospect, I took it out of planned descent mode by doing that. 2) my not backing up beginning of descent point with manual calculations. No excuse except perhaps fatigue. (This was a red-eye flight from sfo-phl that was delayed in sfo due to late arrival of aircraft. Departed sfo at XX38 am local time.) 3) failure of captain to back me up. Due also, I think, to back side of the clock flying. Action: vow not to be lulled into a sense of complacency with FMC. Something I normally don't do. But for whatever reason, it happened this time.

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Original NASA ASRS Text

Title: MLG ACFT CLRED FOR XING RESTR, FO PROGRAMS FMC FOR VNAV DSCNT. CAPT LEAVES COCKPIT. ACFT FAILS TO DSND AND XING RESTR MISSED. FMC PROGRAMMING ERROR.

Narrative: WE WERE GIVEN CLRNC TO CROSS COFAX AT FL250 (WE WERE AT FL310 AT THE TIME). I WAS THE PF. I PROGRAMMED COFAX AT FL250 INTO THE FMC AND VERIFIED THAT I WAS ON VNAV. A FEW MINS LATER THE CAPT STATED HE WAS GOING TO GO TO THE BATHROOM AND GOT UP. JUST AS HE STARTED OUT THE COCKPIT DOOR, I LOOKED DOWN AND REALIZED WE WERE 1 MI FROM COFAX. FOR WHATEVER REASON, THE FMC/AUTOPLT DID NOT START THE DSCNT (STILL WAS ANNUNCIATING VNAV) AND I FAILED TO BACK UP THE MACHINE WITH BASIC AIRMANSHIP. I IMMEDIATELY STARTED DOWN MANUALLY, NOTIFIED ATC THAT I WAS STARTING OUT OF FL310 AT THIS TIME AND APOLOGIZED FOR MISSING THE XING RESTR. HE SAID NO PROB, DSND AND MAINTAIN FL250, AND CONTACT NEW YORK ON 132.2. UPON CONTACT, THEY CLRED US FOR DIRECT LRP AND A FURTHER DSCNT WITH NO XING RESTRS. CONTRIBUTING FACTORS: 1) WE HAD EARLIER BEEN SLOWED DOWN BY ATC TO 250 KTS WHICH I PROGRAMMED INTO THE FMC. THEN WHEN WE WERE GIVEN NORMAL SPD, I COULDN'T GET IT OUT. CAPT SAID LOOK AT CRUISE DSCNT PAGE -- THERE IT WAS. I TOOK IT OUT, PUT BACK ECONOMY CRUISE DSCNT AND THOUGHT EVERYTHING WAS OK. I THINK, IN RETROSPECT, I TOOK IT OUT OF PLANNED DSCNT MODE BY DOING THAT. 2) MY NOT BACKING UP BEGINNING OF DSCNT POINT WITH MANUAL CALCULATIONS. NO EXCUSE EXCEPT PERHAPS FATIGUE. (THIS WAS A RED-EYE FLT FROM SFO-PHL THAT WAS DELAYED IN SFO DUE TO LATE ARR OF ACFT. DEPARTED SFO AT XX38 AM LCL TIME.) 3) FAILURE OF CAPT TO BACK ME UP. DUE ALSO, I THINK, TO BACK SIDE OF THE CLOCK FLYING. ACTION: VOW NOT TO BE LULLED INTO A SENSE OF COMPLACENCY WITH FMC. SOMETHING I NORMALLY DON'T DO. BUT FOR WHATEVER REASON, IT HAPPENED THIS TIME.

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.