Narrative:

Fuel was added just prior to departure due to en route WX and possible destination WX. The dispatcher changed the computer flight plan for the new fuel load, but did not notice that a new route of flight was also generated and filed with ATC, therefore the crew was not advised of the route change. After departure, ZLA issued vectors northbound for traffic and subsequently cleared the flight to pke on course. Flight advised lax that pke was not on the route. Lax read back the route it had on file which was in disagreement with the crew's flight plan. At this time, the captain called company to resolve the problem while the first officer (who was flying the leg) consulted en route charts for the rerte. The flight had been cleared to FL330, but requested FL290 due to gross weight and FL290 was assigned. The aircraft was level at FL290 for approximately 10 mins when the route discrepancy became apparently. Sometime during the period of resolving the rerte, the autoplt MCP entered an uncommanded altitude of FL320. The aircraft entered a subtle an unnoticed climb. Center questioned the altitude as we approached FL302. The crew acknowledged and corrected back to FL290. This incident is just one of many reports of the air carrier medium large transport X advanced technology aircraft autoplt MCP entering uncommanded altitudes in the display window. I personally have observed this happening when aircraft power sources where changed on the ground, but this is the first time I ever saw it happen after the aircraft was stable in cruise flight. Supplemental information from acn 154643: I asked the first officer if he had reset the altitude to which he replied that he had not, and I knew that I had not changed it. I then asked a jump seat rider (also an medium large transport X type captain) if he had seen any changes or noticed the climb. He replied that we had been level for about 10 mins at FL290. At the time we were level at FL290, the autoplt was engaged, VNAV and LNAV were engaged, the altitude annunciator was set at 29000' and the FMC was still programmed for cruise at FL330. I suggest that the altitude portion as well as the autoplt climb and descent commands pertaining to the MCP on the AFDS of the medium large transport X be redesigned. Callback conversation with reporter revealed the following: callback conducted to get more information about operation of AFDS and the altitude preselector/alerter. Captain noted that there is a tendency for the alerter to jump from one altitude to another, both in the aircraft and in the simulator (captain is also a simulator instrument). He further noted that the altitude preselect knob lacks a sufficiently positive detent, suggesting that this may be the primary source of the problem. Uncommanded altitude selector jumps are most commonly 1000'. The reporter also commented that he felt the MCP lighting lights was inadequate for night operations.

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Original NASA ASRS Text

Title: FLT CREW OF ACR ADVTECH MLG EXPERIENCES UNCOMMANDED ALT EXCURSION AT CRUISE.

Narrative: FUEL WAS ADDED JUST PRIOR TO DEP DUE TO ENRTE WX AND POSSIBLE DEST WX. THE DISPATCHER CHANGED THE COMPUTER FLT PLAN FOR THE NEW FUEL LOAD, BUT DID NOT NOTICE THAT A NEW RTE OF FLT WAS ALSO GENERATED AND FILED WITH ATC, THEREFORE THE CREW WAS NOT ADVISED OF THE RTE CHANGE. AFTER DEP, ZLA ISSUED VECTORS NBND FOR TFC AND SUBSEQUENTLY CLRED THE FLT TO PKE ON COURSE. FLT ADVISED LAX THAT PKE WAS NOT ON THE RTE. LAX READ BACK THE RTE IT HAD ON FILE WHICH WAS IN DISAGREEMENT WITH THE CREW'S FLT PLAN. AT THIS TIME, THE CAPT CALLED COMPANY TO RESOLVE THE PROB WHILE THE F/O (WHO WAS FLYING THE LEG) CONSULTED ENRTE CHARTS FOR THE RERTE. THE FLT HAD BEEN CLRED TO FL330, BUT REQUESTED FL290 DUE TO GROSS WT AND FL290 WAS ASSIGNED. THE ACFT WAS LEVEL AT FL290 FOR APPROX 10 MINS WHEN THE RTE DISCREPANCY BECAME APPARENTLY. SOMETIME DURING THE PERIOD OF RESOLVING THE RERTE, THE AUTOPLT MCP ENTERED AN UNCOMMANDED ALT OF FL320. THE ACFT ENTERED A SUBTLE AN UNNOTICED CLB. CENTER QUESTIONED THE ALT AS WE APCHED FL302. THE CREW ACKNOWLEDGED AND CORRECTED BACK TO FL290. THIS INCIDENT IS JUST ONE OF MANY RPTS OF THE ACR MLG X ADVANCED TECHNOLOGY ACFT AUTOPLT MCP ENTERING UNCOMMANDED ALTS IN THE DISPLAY WINDOW. I PERSONALLY HAVE OBSERVED THIS HAPPENING WHEN ACFT PWR SOURCES WHERE CHANGED ON THE GND, BUT THIS IS THE FIRST TIME I EVER SAW IT HAPPEN AFTER THE ACFT WAS STABLE IN CRUISE FLT. SUPPLEMENTAL INFO FROM ACN 154643: I ASKED THE F/O IF HE HAD RESET THE ALT TO WHICH HE REPLIED THAT HE HAD NOT, AND I KNEW THAT I HAD NOT CHANGED IT. I THEN ASKED A JUMP SEAT RIDER (ALSO AN MLG X TYPE CAPT) IF HE HAD SEEN ANY CHANGES OR NOTICED THE CLB. HE REPLIED THAT WE HAD BEEN LEVEL FOR ABOUT 10 MINS AT FL290. AT THE TIME WE WERE LEVEL AT FL290, THE AUTOPLT WAS ENGAGED, VNAV AND LNAV WERE ENGAGED, THE ALT ANNUNCIATOR WAS SET AT 29000' AND THE FMC WAS STILL PROGRAMMED FOR CRUISE AT FL330. I SUGGEST THAT THE ALT PORTION AS WELL AS THE AUTOPLT CLB AND DSNT COMMANDS PERTAINING TO THE MCP ON THE AFDS OF THE MLG X BE REDESIGNED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: CALLBACK CONDUCTED TO GET MORE INFO ABOUT OPERATION OF AFDS AND THE ALT PRESELECTOR/ALERTER. CAPT NOTED THAT THERE IS A TENDENCY FOR THE ALERTER TO JUMP FROM ONE ALT TO ANOTHER, BOTH IN THE ACFT AND IN THE SIMULATOR (CAPT IS ALSO A SIMULATOR INSTR). HE FURTHER NOTED THAT THE ALT PRESELECT KNOB LACKS A SUFFICIENTLY POSITIVE DETENT, SUGGESTING THAT THIS MAY BE THE PRIMARY SOURCE OF THE PROB. UNCOMMANDED ALT SELECTOR JUMPS ARE MOST COMMONLY 1000'. THE RPTR ALSO COMMENTED THAT HE FELT THE MCP LIGHTING LIGHTS WAS INADEQUATE FOR NIGHT OPS.

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.