Narrative:

Flying the civet two profile descent to los angeles runway 25L, we descended 400' below the 10000' crossing altitude at arnes. How did this happen? I suppose the wizardry of the 'glass cockpit' and two newcomers who were not aggressive enough intervening when the computer did other than what they expected. I was qualified on the widebody transport less than a month, having come from the heavy transport. The first officer had less than 2 months experience in FMC aircraft. Following several ATC interruptions of our planned descent with intermediate level offs, we were finally cleared for the civet 2 profile. Speed brakes were required to capture the profile from above. Once captured, or we believed captured, we engaged vertical navigation, expecting the aircraft to fly the profile as stored in the FMC and displayed on the legs page of the FMC. We also anticipated the aircraft would observe the altitude stepdown restrictions at civet, arnes, suzzi and fuelr. After a moment's discussion, the first officer and I decided to set the mode control panel altitude window to 8000', the final altitude of the profile. Approaching civet, all appeared normal. We were in the altitude window, below FL180, just above the 14000' floor approaching arnes it was apparent we would arrive at 10000' several mi prior to the fix. I was watching to see how it would handle this, expecting it to level at 10000' until arnes. The nature of these machines, unlike a pilot, is to maintain a high rate of descent until the capture zone, then make a rather abrupt level off. It did not level. At 10000' it pushed right through the altitude. As soon as it was obvious it was not leveling, I went for the altitude hold switch, hit the heading hold switch by mistake, bounced off it to the altitude hold switch. By now we were below 'ten'. To initiate recovery, I next pushed vertical speed and dialed a climb setting. The result was a descent 400' below desired level off before I got it reversed. What did I learn from this? At least 2 things. One...do not set the end altitude of a profile in the mode control panel window. Now I set each stepdown altitude of the profile in sequence. Two...in a deteriorating situation, do not hesitate or delay if necessary, reverting to old heavy transport skills and punch off the autoplt, manually fly the aircraft to position, then reengage automation as appropriate.

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Original NASA ASRS Text

Title: ACR WDB ALT DEVIATION OVERSHOT ALT CROSSING RESTRICTION ON PROFILE DESCENT INTO LAX.

Narrative: FLYING THE CIVET TWO PROFILE DSNT TO LOS ANGELES RWY 25L, WE DSNDED 400' BELOW THE 10000' XING ALT AT ARNES. HOW DID THIS HAPPEN? I SUPPOSE THE WIZARDRY OF THE 'GLASS COCKPIT' AND TWO NEWCOMERS WHO WERE NOT AGGRESSIVE ENOUGH INTERVENING WHEN THE COMPUTER DID OTHER THAN WHAT THEY EXPECTED. I WAS QUALIFIED ON THE WDB LESS THAN A MONTH, HAVING COME FROM THE HVT. THE F/O HAD LESS THAN 2 MONTHS EXPERIENCE IN FMC ACFT. FOLLOWING SEVERAL ATC INTERRUPTIONS OF OUR PLANNED DSNT WITH INTERMEDIATE LEVEL OFFS, WE WERE FINALLY CLRED FOR THE CIVET 2 PROFILE. SPD BRAKES WERE REQUIRED TO CAPTURE THE PROFILE FROM ABOVE. ONCE CAPTURED, OR WE BELIEVED CAPTURED, WE ENGAGED VERT NAV, EXPECTING THE ACFT TO FLY THE PROFILE AS STORED IN THE FMC AND DISPLAYED ON THE LEGS PAGE OF THE FMC. WE ALSO ANTICIPATED THE ACFT WOULD OBSERVE THE ALT STEPDOWN RESTRICTIONS AT CIVET, ARNES, SUZZI AND FUELR. AFTER A MOMENT'S DISCUSSION, THE F/O AND I DECIDED TO SET THE MODE CTL PANEL ALT WINDOW TO 8000', THE FINAL ALT OF THE PROFILE. APCHING CIVET, ALL APPEARED NORMAL. WE WERE IN THE ALT WINDOW, BELOW FL180, JUST ABOVE THE 14000' FLOOR APCHING ARNES IT WAS APPARENT WE WOULD ARRIVE AT 10000' SEVERAL MI PRIOR TO THE FIX. I WAS WATCHING TO SEE HOW IT WOULD HANDLE THIS, EXPECTING IT TO LEVEL AT 10000' UNTIL ARNES. THE NATURE OF THESE MACHINES, UNLIKE A PLT, IS TO MAINTAIN A HIGH RATE OF DSNT UNTIL THE CAPTURE ZONE, THEN MAKE A RATHER ABRUPT LEVEL OFF. IT DID NOT LEVEL. AT 10000' IT PUSHED RIGHT THROUGH THE ALT. AS SOON AS IT WAS OBVIOUS IT WAS NOT LEVELING, I WENT FOR THE ALT HOLD SWITCH, HIT THE HDG HOLD SWITCH BY MISTAKE, BOUNCED OFF IT TO THE ALT HOLD SWITCH. BY NOW WE WERE BELOW 'TEN'. TO INITIATE RECOVERY, I NEXT PUSHED VERT SPD AND DIALED A CLB SETTING. THE RESULT WAS A DSNT 400' BELOW DESIRED LEVEL OFF BEFORE I GOT IT REVERSED. WHAT DID I LEARN FROM THIS? AT LEAST 2 THINGS. ONE...DO NOT SET THE END ALT OF A PROFILE IN THE MODE CTL PANEL WINDOW. NOW I SET EACH STEPDOWN ALT OF THE PROFILE IN SEQUENCE. TWO...IN A DETERIORATING SITUATION, DO NOT HESITATE OR DELAY IF NECESSARY, REVERTING TO OLD HVT SKILLS AND PUNCH OFF THE AUTOPLT, MANUALLY FLY THE ACFT TO POS, THEN REENGAGE AUTOMATION AS APPROPRIATE.

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.