Narrative:

Event #1: ATC had cleared us to 'lax via sjc 5. Moony ave direct fim direct lax.' upon contacting sjc ATC tower for takeoff clearance we were instructed to 'taxi into position and hold on 30L, on departure fly runway heading and maintain 3000.' shortly after we got takeoff clearance, normal takeoff, then switched to bay departure. Initial contact was established. Upon reaching 3000' the controller called us again: 'cleared to 4000, start your right turn.' the autoplt had been turned on below 2000' MSL. Since our latest clearance had only specified heading and altitude, I read back, 'cleared to 4000' and start what right turn?' controller: 'oh yeah, I guess I did give you runway heading...turn right heading 120 degrees.' the turn was begun and I noticed that the altitude was 3600' and vertical speed 4000 FPM, and high deck angle. I asked the captain whether he had copied the clearance to 4000'. 'Yeah, it's got it,' he replied as we both watched the altitude go through 4000' and the autoplt had still not reduced the pitch angle. The captain disconnected autoplt and leveled manually with a 350' overshoot. Supplemental information from acn 104510: passing 3500' the copilot asked if the aircraft would level off and I told him I had it if it didn't. The yellow altitude light was out and I didn't notice if altitude capture was annunciated. At 3800' it was apparent the autoplt was not leveling the aircraft and I disconnected the autoplt and began the pushover. I leveled off at 4200' on my altimeter. I asked the copilot if he had armed the altitude when we changed from 3000 to 4000' and he said he couldn't swear to it. I am 80% sure it was armed and dropped off. In the first case I believe the altitude arming mode in the medium large transport Z is unsafe. I flew a widebody transport before transitioning and it never dropped an altitude and has greater climb capability than the medium large transport. The first officer was very experienced in the aircraft and I'm sure he armed the altitude. I recommend a software change in the flight director of the medium large transport to prevent further problems with altitude capture. While debriefing the events I asked the copilot if he had ever filed a NASA report and he told me that in the last 3 yrs he has filed 8 altitude busts. After talking to other pilots, both capts and first officer's, I find that this is not an unusual number. I am amazed at the altitude busts in this aircraft and the perception that it will probably happen more times because of the system's proclivity to disarm itself. This is an area that needs further study and evaluation.

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Original NASA ASRS Text

Title: ACR MLG OVERSHOT ALT ON CLIMB.

Narrative: EVENT #1: ATC HAD CLRED US TO 'LAX VIA SJC 5. MOONY AVE DIRECT FIM DIRECT LAX.' UPON CONTACTING SJC ATC TWR FOR TKOF CLRNC WE WERE INSTRUCTED TO 'TAXI INTO POS AND HOLD ON 30L, ON DEP FLY RWY HDG AND MAINTAIN 3000.' SHORTLY AFTER WE GOT TKOF CLRNC, NORMAL TKOF, THEN SWITCHED TO BAY DEP. INITIAL CONTACT WAS ESTABLISHED. UPON REACHING 3000' THE CTLR CALLED US AGAIN: 'CLRED TO 4000, START YOUR RIGHT TURN.' THE AUTOPLT HAD BEEN TURNED ON BELOW 2000' MSL. SINCE OUR LATEST CLRNC HAD ONLY SPECIFIED HDG AND ALT, I READ BACK, 'CLRED TO 4000' AND START WHAT RIGHT TURN?' CTLR: 'OH YEAH, I GUESS I DID GIVE YOU RWY HDG...TURN RIGHT HDG 120 DEGS.' THE TURN WAS BEGUN AND I NOTICED THAT THE ALT WAS 3600' AND VERT SPD 4000 FPM, AND HIGH DECK ANGLE. I ASKED THE CAPT WHETHER HE HAD COPIED THE CLRNC TO 4000'. 'YEAH, IT'S GOT IT,' HE REPLIED AS WE BOTH WATCHED THE ALT GO THROUGH 4000' AND THE AUTOPLT HAD STILL NOT REDUCED THE PITCH ANGLE. THE CAPT DISCONNECTED AUTOPLT AND LEVELED MANUALLY WITH A 350' OVERSHOOT. SUPPLEMENTAL INFO FROM ACN 104510: PASSING 3500' THE COPLT ASKED IF THE ACFT WOULD LEVEL OFF AND I TOLD HIM I HAD IT IF IT DIDN'T. THE YELLOW ALT LIGHT WAS OUT AND I DIDN'T NOTICE IF ALT CAPTURE WAS ANNUNCIATED. AT 3800' IT WAS APPARENT THE AUTOPLT WAS NOT LEVELING THE ACFT AND I DISCONNECTED THE AUTOPLT AND BEGAN THE PUSHOVER. I LEVELED OFF AT 4200' ON MY ALTIMETER. I ASKED THE COPLT IF HE HAD ARMED THE ALT WHEN WE CHANGED FROM 3000 TO 4000' AND HE SAID HE COULDN'T SWEAR TO IT. I AM 80% SURE IT WAS ARMED AND DROPPED OFF. IN THE FIRST CASE I BELIEVE THE ALT ARMING MODE IN THE MLG Z IS UNSAFE. I FLEW A WDB BEFORE TRANSITIONING AND IT NEVER DROPPED AN ALT AND HAS GREATER CLB CAPABILITY THAN THE MLG. THE F/O WAS VERY EXPERIENCED IN THE ACFT AND I'M SURE HE ARMED THE ALT. I RECOMMEND A SOFTWARE CHANGE IN THE FLT DIRECTOR OF THE MLG TO PREVENT FURTHER PROBS WITH ALT CAPTURE. WHILE DEBRIEFING THE EVENTS I ASKED THE COPLT IF HE HAD EVER FILED A NASA RPT AND HE TOLD ME THAT IN THE LAST 3 YRS HE HAS FILED 8 ALT BUSTS. AFTER TALKING TO OTHER PLTS, BOTH CAPTS AND F/O'S, I FIND THAT THIS IS NOT AN UNUSUAL NUMBER. I AM AMAZED AT THE ALT BUSTS IN THIS ACFT AND THE PERCEPTION THAT IT WILL PROBABLY HAPPEN MORE TIMES BECAUSE OF THE SYSTEM'S PROCLIVITY TO DISARM ITSELF. THIS IS AN AREA THAT NEEDS FURTHER STUDY AND EVALUATION.

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.