Narrative:

While flying the runway 25 profile descent/29 palms transition, the aircraft I was flying was allowed to descend to 11500' MSL prior to civet intersection (14000' MSL crossing restriction). Left.a. Center notified us of the altitude deviation at XA24Z, approximately 4 mi east of the civet intersection, at which time we initiated a climb back towards 14000'. We crossed civet while transitioning from a climb back T the profiled descent. There wasn't any traffic conflict caused by the excursion. The rest of the approach and landing was uneventful. A contributing factor, other than a total lack of crew awareness, was that although I had programmed the FMC for the profile descent, (complete with altitude and airspeed restrictions) when I put in an altitude 50' above the touchdown zone of runway 25 the computer wiped out all restrictions except the 50' one and neither the captain nor myself noticed at that time. Also, I had set the minimum altitude in the altitude display window on the mode control panel to 100' (to match the 50' above touchdown zone) and to allow the FMC to fly the profile by itself west/O being stopped by the altitude set in the altitude display window. We've since determined that with a profile descent selected like we did and an altitude above the touchdown zone set in, if the profile is reselected all restrictions on the profile in addition to the one added above the touchdown zone will be reinstated. Thus the computer/airplane will comply with the restrictions on the profile even if the altitude in adw is set to 0'. Unfortunately, none of this was taught in ground school. The mistake was made by me, a crewmember, and the responsibility of flying the profile was still mine, whether the computer was working or not. A little more attention to detail on my part in the future is the best preventive measure I can think of. Callback conversation with reporter revealed the following: since incident, reporter has talked to several companies and they report the addition of the threshold crossing altitude in the FMC should not have knocked out the other crossing altitudes already in the FMC. This was apparently a glitch, but company is checking on problem.

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Original NASA ASRS Text

Title: ACR WDB WITH ADVANCED TECHNOLOGY FMC OVERSHOT CROSSING ALT OF PROFILE WHEN FLT CREW ENTERED THRESHOLD CROSSING ALT PREVIOUSLY ENTERED ALTS WERE WIPED OUT.

Narrative: WHILE FLYING THE RWY 25 PROFILE DSCNT/29 PALMS TRANSITION, THE ACFT I WAS FLYING WAS ALLOWED TO DSND TO 11500' MSL PRIOR TO CIVET INTXN (14000' MSL XING RESTRICTION). L.A. CENTER NOTIFIED US OF THE ALT DEVIATION AT XA24Z, APPROX 4 MI E OF THE CIVET INTXN, AT WHICH TIME WE INITIATED A CLB BACK TOWARDS 14000'. WE CROSSED CIVET WHILE TRANSITIONING FROM A CLB BACK T THE PROFILED DSCNT. THERE WASN'T ANY TFC CONFLICT CAUSED BY THE EXCURSION. THE REST OF THE APCH AND LNDG WAS UNEVENTFUL. A CONTRIBUTING FACTOR, OTHER THAN A TOTAL LACK OF CREW AWARENESS, WAS THAT ALTHOUGH I HAD PROGRAMMED THE FMC FOR THE PROFILE DSCNT, (COMPLETE WITH ALT AND AIRSPD RESTRICTIONS) WHEN I PUT IN AN ALT 50' ABOVE THE TOUCHDOWN ZONE OF RWY 25 THE COMPUTER WIPED OUT ALL RESTRICTIONS EXCEPT THE 50' ONE AND NEITHER THE CAPT NOR MYSELF NOTICED AT THAT TIME. ALSO, I HAD SET THE MINIMUM ALT IN THE ALT DISPLAY WINDOW ON THE MODE CTL PANEL TO 100' (TO MATCH THE 50' ABOVE TOUCHDOWN ZONE) AND TO ALLOW THE FMC TO FLY THE PROFILE BY ITSELF W/O BEING STOPPED BY THE ALT SET IN THE ALT DISPLAY WINDOW. WE'VE SINCE DETERMINED THAT WITH A PROFILE DSCNT SELECTED LIKE WE DID AND AN ALT ABOVE THE TOUCHDOWN ZONE SET IN, IF THE PROFILE IS RESELECTED ALL RESTRICTIONS ON THE PROFILE IN ADDITION TO THE ONE ADDED ABOVE THE TOUCHDOWN ZONE WILL BE REINSTATED. THUS THE COMPUTER/AIRPLANE WILL COMPLY WITH THE RESTRICTIONS ON THE PROFILE EVEN IF THE ALT IN ADW IS SET TO 0'. UNFORTUNATELY, NONE OF THIS WAS TAUGHT IN GND SCHOOL. THE MISTAKE WAS MADE BY ME, A CREWMEMBER, AND THE RESPONSIBILITY OF FLYING THE PROFILE WAS STILL MINE, WHETHER THE COMPUTER WAS WORKING OR NOT. A LITTLE MORE ATTN TO DETAIL ON MY PART IN THE FUTURE IS THE BEST PREVENTIVE MEASURE I CAN THINK OF. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: SINCE INCIDENT, RPTR HAS TALKED TO SEVERAL COMPANIES AND THEY RPT THE ADDITION OF THE THRESHOLD XING ALT IN THE FMC SHOULD NOT HAVE KNOCKED OUT THE OTHER XING ALTS ALREADY IN THE FMC. THIS WAS APPARENTLY A GLITCH, BUT COMPANY IS CHKING ON PROB.

Data retrieved from NASA's ASRS site as of August 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.