Narrative:

On nov/xa/99, our flight departed bur at XF54Z to sfo. It was the 3RD leg of a 4 leg sequence. The day had originated at lax at XA57Z that morning. I was the captain and PNF. Departure, climb out and initial cruise were normal. After approximately 20 mins at cruise, both engine throttles began to oscillate forward and aft approximately 2% N1 RPM. Autoplt and autothrottles were engaged. I turned both engine pmc (performance management computer) switches 'off' and throttles split approximately 2 knobs width for the autothrottles to maintain the same N1 RPM on each engine. I pushed both pmc switches back to 'on' and throttles returned to their previous position and started to oscillate once again. I asked the first officer who was the PF to turn the autothrottles 'off.' he did so and the oscillation ceased. There was no procedural reference in our flight manual to cover this situation. The #1 engine in our aircraft had been changed 2 days prior because of in-flight compressor stalls. Given this history, I became a little concerned about the situation with the engines. Both engines were operating normally except for the oscillations with the autothrottles engaged and the abnormal split when the pmc's were selected to 'off'. Both the first officer and I concurred that we were not in an emergency situation, but that we needed to enter a maintenance write-up in the logbook. At this time, ZOA advised us that there was ATC flow control into sfo and issued us holding instructions at skunk on the big sur arrival. Efc was XH20Z. En route to skunk, we were instructed to descend from FL310 to 12000 ft. Holding pattern entry and descent to 12000 ft were uneventful. While in the holding pattern, I had taken out the fault reporting manual and was attempting to find a code to send to maintenance via ACARS. Since our engine problem was not specifically covered by one code, I was attempting to determine the best way to document our problem for maintenance. At approximately XG50Z, as we approached skunk on an inbound leg, ZOA issued us a clearance to descend. I looked up from the fault reporting manual and acknowledged the clearance. Regrettably, I do not now recall what altitude ZOA issued us. Because my seat was back in order to have the fault reporting manual in my lap, I could not reach the altitude set knob on the MCP. I motioned for the first officer to change the altitude from 12000 ft to the new altitude. I then went back to reading the fault reporting manual. As we were rolling out onto the outbound leg of the holding pattern, ZOA called us and asked us 'aircraft X, confirm level at 11000 ft.' I immediately looked up from the fault reporting manual, and saw our altitude at 10700 ft, descending at approximately 1200 FPM and 10000 ft set in the MCP altitude window. I answered, 'aircraft X descending to 10000 ft assigned.' I instructed the first officer to level off immediately and we leveled at 10500 ft. I called center again and said 'oakland, say assigned altitude for aircraft X.' as I completed my transmission, I heard the last portion of a call ZOA had made to us which was '...maintain your outbound leg.' I immediately responded back 'ZOA, sir say assigned altitude for aircraft X.' oakland replied 'maintain 10000 ft.' I instructed the first officer to descend to 10000 ft. The first officer was very emphatic to me that the cleared altitude was 10000 ft not 11000 ft. Approximately 2 mins later, ZOA issued us instructions for a left turn direct skunk, flying the remainder of the big sur to sfo, maintain 10000 ft. At no time did ZOA indicate that we had lost traffic separation from another aircraft. I do not know if the confusion related above was our misunderstanding or ZOA's. Prior to the altitude discrepancy call, I was concerned about the engines and the possible impact that a lengthy maintenance delay would cause the remainder of our day. We were scheduled to go to pdx after sfo and our crew day had already been lengthened by a 1 hour and 30 min ATC flow delay in bur. Not only was I trying to extract a proper code from the complicated fault reporting manual, but I also was trying to recall engine parameter numbers, altitudes, airspds and autoflt conditions we experienced during our engine problems. This, along with the fact that I had been awake since XA00 local, obviously resulted in the confusion between us and ZOA. Again, my first officer insisted that our cleared altitude was 10000 ft, not 11000 ft. However, because of my occupation with the engine situation, I do not recall now or then, what altitude we were cleared to or what altitude assignment I read back to ZOA. This incident could have been avoided if I would have adhered to our airline's SOP which specifically states that the PNF will read back the assigned altitude, change the assigned altitude on the MCP and the PF will then verbally acknowledge the new altitude and point to the MCP. Because my seat was back and I could not reach the MCP, I had the first officer change the altitude. I did not specifically watch him make the change because of my preoccupation with reading the fault reporting manual. I felt at the time that it was necessary to enter a proper logbook discrepancy and send a code prior to landing. In retrospect, there was not a necessity for me to do so, especially given the fact that I became totally detached from monitoring our situation.

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Original NASA ASRS Text

Title: AN ACR CAPT, PNF, BECAME DISTRACTED WITH A MAINT BOOK DURING AN ALT CHANGE AND ADMITTED THAT HE DID NOT FOLLOW HIS COMPANY'S SOP FOR BACKING UP THE PF.

Narrative: ON NOV/XA/99, OUR FLT DEPARTED BUR AT XF54Z TO SFO. IT WAS THE 3RD LEG OF A 4 LEG SEQUENCE. THE DAY HAD ORIGINATED AT LAX AT XA57Z THAT MORNING. I WAS THE CAPT AND PNF. DEP, CLBOUT AND INITIAL CRUISE WERE NORMAL. AFTER APPROX 20 MINS AT CRUISE, BOTH ENG THROTTLES BEGAN TO OSCILLATE FORWARD AND AFT APPROX 2% N1 RPM. AUTOPLT AND AUTOTHROTTLES WERE ENGAGED. I TURNED BOTH ENG PMC (PERFORMANCE MGMNT COMPUTER) SWITCHES 'OFF' AND THROTTLES SPLIT APPROX 2 KNOBS WIDTH FOR THE AUTOTHROTTLES TO MAINTAIN THE SAME N1 RPM ON EACH ENG. I PUSHED BOTH PMC SWITCHES BACK TO 'ON' AND THROTTLES RETURNED TO THEIR PREVIOUS POS AND STARTED TO OSCILLATE ONCE AGAIN. I ASKED THE FO WHO WAS THE PF TO TURN THE AUTOTHROTTLES 'OFF.' HE DID SO AND THE OSCILLATION CEASED. THERE WAS NO PROCEDURAL REF IN OUR FLT MANUAL TO COVER THIS SIT. THE #1 ENG IN OUR ACFT HAD BEEN CHANGED 2 DAYS PRIOR BECAUSE OF INFLT COMPRESSOR STALLS. GIVEN THIS HISTORY, I BECAME A LITTLE CONCERNED ABOUT THE SIT WITH THE ENGS. BOTH ENGS WERE OPERATING NORMALLY EXCEPT FOR THE OSCILLATIONS WITH THE AUTOTHROTTLES ENGAGED AND THE ABNORMAL SPLIT WHEN THE PMC'S WERE SELECTED TO 'OFF'. BOTH THE FO AND I CONCURRED THAT WE WERE NOT IN AN EMER SIT, BUT THAT WE NEEDED TO ENTER A MAINT WRITE-UP IN THE LOGBOOK. AT THIS TIME, ZOA ADVISED US THAT THERE WAS ATC FLOW CTL INTO SFO AND ISSUED US HOLDING INSTRUCTIONS AT SKUNK ON THE BIG SUR ARR. EFC WAS XH20Z. ENRTE TO SKUNK, WE WERE INSTRUCTED TO DSND FROM FL310 TO 12000 FT. HOLDING PATTERN ENTRY AND DSCNT TO 12000 FT WERE UNEVENTFUL. WHILE IN THE HOLDING PATTERN, I HAD TAKEN OUT THE FAULT RPTING MANUAL AND WAS ATTEMPTING TO FIND A CODE TO SEND TO MAINT VIA ACARS. SINCE OUR ENG PROB WAS NOT SPECIFICALLY COVERED BY ONE CODE, I WAS ATTEMPTING TO DETERMINE THE BEST WAY TO DOCUMENT OUR PROB FOR MAINT. AT APPROX XG50Z, AS WE APCHED SKUNK ON AN INBOUND LEG, ZOA ISSUED US A CLRNC TO DSND. I LOOKED UP FROM THE FAULT RPTING MANUAL AND ACKNOWLEDGED THE CLRNC. REGRETTABLY, I DO NOT NOW RECALL WHAT ALT ZOA ISSUED US. BECAUSE MY SEAT WAS BACK IN ORDER TO HAVE THE FAULT RPTING MANUAL IN MY LAP, I COULD NOT REACH THE ALT SET KNOB ON THE MCP. I MOTIONED FOR THE FO TO CHANGE THE ALT FROM 12000 FT TO THE NEW ALT. I THEN WENT BACK TO READING THE FAULT RPTING MANUAL. AS WE WERE ROLLING OUT ONTO THE OUTBOUND LEG OF THE HOLDING PATTERN, ZOA CALLED US AND ASKED US 'ACFT X, CONFIRM LEVEL AT 11000 FT.' I IMMEDIATELY LOOKED UP FROM THE FAULT RPTING MANUAL, AND SAW OUR ALT AT 10700 FT, DSNDING AT APPROX 1200 FPM AND 10000 FT SET IN THE MCP ALT WINDOW. I ANSWERED, 'ACFT X DSNDING TO 10000 FT ASSIGNED.' I INSTRUCTED THE FO TO LEVEL OFF IMMEDIATELY AND WE LEVELED AT 10500 FT. I CALLED CTR AGAIN AND SAID 'OAKLAND, SAY ASSIGNED ALT FOR ACFT X.' AS I COMPLETED MY XMISSION, I HEARD THE LAST PORTION OF A CALL ZOA HAD MADE TO US WHICH WAS '...MAINTAIN YOUR OUTBOUND LEG.' I IMMEDIATELY RESPONDED BACK 'ZOA, SIR SAY ASSIGNED ALT FOR ACFT X.' OAKLAND REPLIED 'MAINTAIN 10000 FT.' I INSTRUCTED THE FO TO DSND TO 10000 FT. THE FO WAS VERY EMPHATIC TO ME THAT THE CLRED ALT WAS 10000 FT NOT 11000 FT. APPROX 2 MINS LATER, ZOA ISSUED US INSTRUCTIONS FOR A L TURN DIRECT SKUNK, FLYING THE REMAINDER OF THE BIG SUR TO SFO, MAINTAIN 10000 FT. AT NO TIME DID ZOA INDICATE THAT WE HAD LOST TFC SEPARATION FROM ANOTHER ACFT. I DO NOT KNOW IF THE CONFUSION RELATED ABOVE WAS OUR MISUNDERSTANDING OR ZOA'S. PRIOR TO THE ALT DISCREPANCY CALL, I WAS CONCERNED ABOUT THE ENGS AND THE POSSIBLE IMPACT THAT A LENGTHY MAINT DELAY WOULD CAUSE THE REMAINDER OF OUR DAY. WE WERE SCHEDULED TO GO TO PDX AFTER SFO AND OUR CREW DAY HAD ALREADY BEEN LENGTHENED BY A 1 HR AND 30 MIN ATC FLOW DELAY IN BUR. NOT ONLY WAS I TRYING TO EXTRACT A PROPER CODE FROM THE COMPLICATED FAULT RPTING MANUAL, BUT I ALSO WAS TRYING TO RECALL ENG PARAMETER NUMBERS, ALTS, AIRSPDS AND AUTOFLT CONDITIONS WE EXPERIENCED DURING OUR ENG PROBS. THIS, ALONG WITH THE FACT THAT I HAD BEEN AWAKE SINCE XA00 LCL, OBVIOUSLY RESULTED IN THE CONFUSION BTWN US AND ZOA. AGAIN, MY FO INSISTED THAT OUR CLRED ALT WAS 10000 FT, NOT 11000 FT. HOWEVER, BECAUSE OF MY OCCUPATION WITH THE ENG SIT, I DO NOT RECALL NOW OR THEN, WHAT ALT WE WERE CLRED TO OR WHAT ALT ASSIGNMENT I READ BACK TO ZOA. THIS INCIDENT COULD HAVE BEEN AVOIDED IF I WOULD HAVE ADHERED TO OUR AIRLINE'S SOP WHICH SPECIFICALLY STATES THAT THE PNF WILL READ BACK THE ASSIGNED ALT, CHANGE THE ASSIGNED ALT ON THE MCP AND THE PF WILL THEN VERBALLY ACKNOWLEDGE THE NEW ALT AND POINT TO THE MCP. BECAUSE MY SEAT WAS BACK AND I COULD NOT REACH THE MCP, I HAD THE FO CHANGE THE ALT. I DID NOT SPECIFICALLY WATCH HIM MAKE THE CHANGE BECAUSE OF MY PREOCCUPATION WITH READING THE FAULT RPTING MANUAL. I FELT AT THE TIME THAT IT WAS NECESSARY TO ENTER A PROPER LOGBOOK DISCREPANCY AND SEND A CODE PRIOR TO LNDG. IN RETROSPECT, THERE WAS NOT A NECESSITY FOR ME TO DO SO, ESPECIALLY GIVEN THE FACT THAT I BECAME TOTALLY DETACHED FROM MONITORING OUR SIT.

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.