Narrative:

Just prior to leaving FL370 for FL230, the first officer had to make a quick trip to the bathroom. We were cleared to cross harty intersection at and maintain FL230. A standard clearance for jfk arrs. Done it a hundred times. I put on oxygen mask and set up radio panel. Sun has just come up and it is a beautiful morning, although very bright with sun in eyes. FMC starts aircraft nose down at the proper descent point for FL230. I call out of FL370. Computer shows aircraft will cross harty intersection 1 mi before harty. Speed is good. At about FL340 first officer returns to cockpit, gets in seat and hooks up. Flight attendant knocks on door, has coffee (not asked for) and wants to know landing time. First officer assumes flying duties. Computer shows aircraft right on proper descent profile. I'm putting oxygen mask away, first officer is getting his coffee, and aircraft is at approximately FL280. ATC asks if we're going to make the harty crossing restr at FL230. I wonder who he asked, and checked the FMC display. Couldn't believe my eyes. Descent rate had changed and it was obvious we couldn't cross harty at FL230. I told the first officer to tell center we couldn't make FL230, assumed the flying duties, took aircraft off autoplt, pulled speed brakes, and attempted to get as low as possible to FL230. Once we said we couldn't make it, the controller indicated that he didn't have our altitude (it had crossed out?) but there was not a problem and would we please descend now so as to cross the next intersection, lendy, at FL190. I believed we crossed harty at FL240. We crossed lendy at FL190 and rest of flight was routine. What caused the problem? Technically, I don't know. FMC was right on descent path at approximately FL330. And then the rate of descent changed. Human factors wise, my failure to continuously monitor the descent rate during all the distractions of first officer returning, unwanted coffee, sun in eyes, oxygen mask stowage was the real culprit here. I assumed the first officer was monitoring, as he had taken over, but he was just as complacent as I was. Once aware we couldn't make the altitude, he seemed devastated. Correcting the situation. From now on, I will brief my crew that all 'potty' breaks must be done before descent from cruise. Once descending, I will never again give the computer credit for brains. I will continuously monitor, even while doing other cockpit duties. And I will make sure my first officer does as well. Thank god, this was early in the morning with very, very little traffic in the area.

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Original NASA ASRS Text

Title: B757 CREW HAD ALT UNDERSHOOT.

Narrative: JUST PRIOR TO LEAVING FL370 FOR FL230, THE FO HAD TO MAKE A QUICK TRIP TO THE BATHROOM. WE WERE CLRED TO CROSS HARTY INTXN AT AND MAINTAIN FL230. A STANDARD CLRNC FOR JFK ARRS. DONE IT A HUNDRED TIMES. I PUT ON OXYGEN MASK AND SET UP RADIO PANEL. SUN HAS JUST COME UP AND IT IS A BEAUTIFUL MORNING, ALTHOUGH VERY BRIGHT WITH SUN IN EYES. FMC STARTS ACFT NOSE DOWN AT THE PROPER DSCNT POINT FOR FL230. I CALL OUT OF FL370. COMPUTER SHOWS ACFT WILL CROSS HARTY INTXN 1 MI BEFORE HARTY. SPD IS GOOD. AT ABOUT FL340 FO RETURNS TO COCKPIT, GETS IN SEAT AND HOOKS UP. FLT ATTENDANT KNOCKS ON DOOR, HAS COFFEE (NOT ASKED FOR) AND WANTS TO KNOW LNDG TIME. FO ASSUMES FLYING DUTIES. COMPUTER SHOWS ACFT RIGHT ON PROPER DSCNT PROFILE. I'M PUTTING OXYGEN MASK AWAY, FO IS GETTING HIS COFFEE, AND ACFT IS AT APPROX FL280. ATC ASKS IF WE'RE GOING TO MAKE THE HARTY XING RESTR AT FL230. I WONDER WHO HE ASKED, AND CHKED THE FMC DISPLAY. COULDN'T BELIEVE MY EYES. DSCNT RATE HAD CHANGED AND IT WAS OBVIOUS WE COULDN'T CROSS HARTY AT FL230. I TOLD THE FO TO TELL CTR WE COULDN'T MAKE FL230, ASSUMED THE FLYING DUTIES, TOOK ACFT OFF AUTOPLT, PULLED SPD BRAKES, AND ATTEMPTED TO GET AS LOW AS POSSIBLE TO FL230. ONCE WE SAID WE COULDN'T MAKE IT, THE CTLR INDICATED THAT HE DIDN'T HAVE OUR ALT (IT HAD CROSSED OUT?) BUT THERE WAS NOT A PROB AND WOULD WE PLEASE DSND NOW SO AS TO CROSS THE NEXT INTXN, LENDY, AT FL190. I BELIEVED WE CROSSED HARTY AT FL240. WE CROSSED LENDY AT FL190 AND REST OF FLT WAS ROUTINE. WHAT CAUSED THE PROB? TECHNICALLY, I DON'T KNOW. FMC WAS RIGHT ON DSCNT PATH AT APPROX FL330. AND THEN THE RATE OF DSCNT CHANGED. HUMAN FACTORS WISE, MY FAILURE TO CONTINUOUSLY MONITOR THE DSCNT RATE DURING ALL THE DISTRACTIONS OF FO RETURNING, UNWANTED COFFEE, SUN IN EYES, OXYGEN MASK STOWAGE WAS THE REAL CULPRIT HERE. I ASSUMED THE FO WAS MONITORING, AS HE HAD TAKEN OVER, BUT HE WAS JUST AS COMPLACENT AS I WAS. ONCE AWARE WE COULDN'T MAKE THE ALT, HE SEEMED DEVASTATED. CORRECTING THE SIT. FROM NOW ON, I WILL BRIEF MY CREW THAT ALL 'POTTY' BREAKS MUST BE DONE BEFORE DSCNT FROM CRUISE. ONCE DSNDING, I WILL NEVER AGAIN GIVE THE COMPUTER CREDIT FOR BRAINS. I WILL CONTINUOUSLY MONITOR, EVEN WHILE DOING OTHER COCKPIT DUTIES. AND I WILL MAKE SURE MY FO DOES AS WELL. THANK GOD, THIS WAS EARLY IN THE MORNING WITH VERY, VERY LITTLE TFC IN THE AREA.

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.