Narrative:

Air carrier XXX (cyyz-lax) descending into lax. We had been cleared direct civet and the civet 4 arrival. Our speed had been 310 KTS. ATC requested 250 KTS. We complied. We were switched to socal approach who assigned us 320 KTS. We complied. Aircraft was being flown in VNAV LNAV with speed brakes extended to maintain profile. After civet, the aircraft leveled and left the profile. I selected flight level change in an attempt to get the aircraft to continue the descent. Because the aircraft was being operated in VNAV, 8000 ft had been set in the altitude window of the autoplt. However, when flight level change was selected, the altitude was not reselected to the 12000 ft restr (at bremr). As such, the aircraft descended below the 12000 ft level to 11000 ft before I realized my mistake. I disconnected autoplt and autothrust, leveled the aircraft at 11000 ft and brought the mistake to the captain's attention. He advised me to maintain the altitude and reacquire the VNAV path and then continue the descent. ATC was not advised nor did they question or call attention to our excursion. I feel that contributing factors to this incident were poor communication/coordination between ATC sectors resulting in massive speed variations. 310 KTS to 250 KTS to 320 KTS to 250 KTS to 210 KTS to 170 KTS within a 20 mi sector. This is already a critical FMS arrival without speed change requests. Speed brakes are required as a normal routine. In this case it was too much for the FMS and required us to rely on a less automated descent (non stop) whereby errors could easily creep in. Our performance was degraded (crew coordination) by a heavily increased workload. Callback conversation with reporter revealed the following information: pilot said he has been to lax 3 times since he submitted his report. On each occasion they have had multiple stars, runway changes, and changes to the point that the aircraft FMC was unable to cope. He considers the lax situation the most difficult of any place he flies in the world. He further states that it has gotten more difficult this summer. Crews on his air carrier begin briefing about 45 mins earlier than normal and try to brief for all possible approachs. This increases cockpit workload and makes it a problem keeping the different approachs separated.

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Original NASA ASRS Text

Title: B767 CREW WAS ASSIGNED 6 SPD CHANGES IN ABOUT 4 MINS. THE ACFT AUTOMATION WAS UNABLE TO HANDLE IT AND AN ALT EXCURSION RESULTED.

Narrative: ACR XXX (CYYZ-LAX) DSNDING INTO LAX. WE HAD BEEN CLRED DIRECT CIVET AND THE CIVET 4 ARR. OUR SPD HAD BEEN 310 KTS. ATC REQUESTED 250 KTS. WE COMPLIED. WE WERE SWITCHED TO SOCAL APCH WHO ASSIGNED US 320 KTS. WE COMPLIED. ACFT WAS BEING FLOWN IN VNAV LNAV WITH SPD BRAKES EXTENDED TO MAINTAIN PROFILE. AFTER CIVET, THE ACFT LEVELED AND LEFT THE PROFILE. I SELECTED FLT LEVEL CHANGE IN AN ATTEMPT TO GET THE ACFT TO CONTINUE THE DSCNT. BECAUSE THE ACFT WAS BEING OPERATED IN VNAV, 8000 FT HAD BEEN SET IN THE ALT WINDOW OF THE AUTOPLT. HOWEVER, WHEN FLT LEVEL CHANGE WAS SELECTED, THE ALT WAS NOT RESELECTED TO THE 12000 FT RESTR (AT BREMR). AS SUCH, THE ACFT DSNDED BELOW THE 12000 FT LEVEL TO 11000 FT BEFORE I REALIZED MY MISTAKE. I DISCONNECTED AUTOPLT AND AUTOTHRUST, LEVELED THE ACFT AT 11000 FT AND BROUGHT THE MISTAKE TO THE CAPT'S ATTN. HE ADVISED ME TO MAINTAIN THE ALT AND REACQUIRE THE VNAV PATH AND THEN CONTINUE THE DSCNT. ATC WAS NOT ADVISED NOR DID THEY QUESTION OR CALL ATTN TO OUR EXCURSION. I FEEL THAT CONTRIBUTING FACTORS TO THIS INCIDENT WERE POOR COM/COORD BTWN ATC SECTORS RESULTING IN MASSIVE SPD VARIATIONS. 310 KTS TO 250 KTS TO 320 KTS TO 250 KTS TO 210 KTS TO 170 KTS WITHIN A 20 MI SECTOR. THIS IS ALREADY A CRITICAL FMS ARR WITHOUT SPD CHANGE REQUESTS. SPD BRAKES ARE REQUIRED AS A NORMAL ROUTINE. IN THIS CASE IT WAS TOO MUCH FOR THE FMS AND REQUIRED US TO RELY ON A LESS AUTOMATED DSCNT (NON STOP) WHEREBY ERRORS COULD EASILY CREEP IN. OUR PERFORMANCE WAS DEGRADED (CREW COORD) BY A HEAVILY INCREASED WORKLOAD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: PLT SAID HE HAS BEEN TO LAX 3 TIMES SINCE HE SUBMITTED HIS RPT. ON EACH OCCASION THEY HAVE HAD MULTIPLE STARS, RWY CHANGES, AND CHANGES TO THE POINT THAT THE ACFT FMC WAS UNABLE TO COPE. HE CONSIDERS THE LAX SIT THE MOST DIFFICULT OF ANY PLACE HE FLIES IN THE WORLD. HE FURTHER STATES THAT IT HAS GOTTEN MORE DIFFICULT THIS SUMMER. CREWS ON HIS ACR BEGIN BRIEFING ABOUT 45 MINS EARLIER THAN NORMAL AND TRY TO BRIEF FOR ALL POSSIBLE APCHS. THIS INCREASES COCKPIT WORKLOAD AND MAKES IT A PROB KEEPING THE DIFFERENT APCHS SEPARATED.

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.