Narrative:

On arrival; I wrote the following write-up in the maintenance logbook. On approach; approximately 2000 ft; autothrottles on engines commanded to accelerate; left engine hung at approach idle; right engine accelerated normally. Appears left engine would not respond to power input then finally accelerated 10-15 seconds after right engine. On arrival; idle thrust at 280 KTS from FL300; cleared via intersection at 17000 ft. At idle thrust 280 KTS; slowed to 250 KTS using speed brakes on path approaching 10000 ft; ATC asked to maintain 250 KTS until advised then cleared us to slow to 220 KTS until advised; speed brakes used to slow. Below 3000 ft cleared to maintain 170 KTS to OM; still at idle on profile descent; speed brakes used to slow. Approaching 170 KTS; first officer stowing speed brakes as autothrottles moved together to maintain commanded speed. Engines did not accelerate immediately; saw command thrust arcs on EICAS. Right engine began to respond and accelerated normally; but left engine hung at idle thrust although autothrottles had moved; were matched and command thrust arcs equal showing required thrust. After approximately 10-15 seconds; left engine finally responded and accelerated to match the right engine. During event; aircraft was on autoplt with autothrottles engaged. Autoplt handled yaw associated with uneven thrust acceleration until thrust finally was symmetrical. Normal approach and landing after event; except for low altitude possible bird strike; which was also entered in maintenance log. After landing; contacted maintenance to advise; debriefed amt in cockpit; then called dispatch. Callback conversation with reporter revealed the following information: the captain advised that the air carrier's maintenance and flight operations departments expended a great deal of effort analyzing fdr data and testing scenarios in the simulator and again in the actual aircraft. Their findings were that the delay in response was due to the PF's (the first officer) arm restricting the throttle from physically advancing. This happened because he was simultaneously slowly retracting the spoilers as the leveloff progressed. Because the spoiler control lever is on the captain's side of the throttle quadrant; the first officer must reach behind or over the throttles at idle (the most probable thrust setting when activating the spoilers/speed brakes). In this case his arm restr the throttle from advancing. It was determined that only a modest amount of pressure (1 pound or 1 1/2 pounds) is required to restrict throttle movement on the engines employed by this carrier. The required pressure was not enough to alert the first officer to the autothrottle's attempt to advance the lever. The air carrier intends to issue a bulletin to the B777 pilots alerting them to this potential.

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Original NASA ASRS Text

Title: B777 ON DSCNT; L ENG DELAY IN ACCELERATION DURING INTERMEDIATE LEVELOFF.

Narrative: ON ARR; I WROTE THE FOLLOWING WRITE-UP IN THE MAINT LOGBOOK. ON APCH; APPROX 2000 FT; AUTOTHROTTLES ON ENGS COMMANDED TO ACCELERATE; L ENG HUNG AT APCH IDLE; R ENG ACCELERATED NORMALLY. APPEARS L ENG WOULD NOT RESPOND TO PWR INPUT THEN FINALLY ACCELERATED 10-15 SECONDS AFTER R ENG. ON ARR; IDLE THRUST AT 280 KTS FROM FL300; CLRED VIA INTXN AT 17000 FT. AT IDLE THRUST 280 KTS; SLOWED TO 250 KTS USING SPD BRAKES ON PATH APCHING 10000 FT; ATC ASKED TO MAINTAIN 250 KTS UNTIL ADVISED THEN CLRED US TO SLOW TO 220 KTS UNTIL ADVISED; SPD BRAKES USED TO SLOW. BELOW 3000 FT CLRED TO MAINTAIN 170 KTS TO OM; STILL AT IDLE ON PROFILE DSCNT; SPD BRAKES USED TO SLOW. APCHING 170 KTS; FO STOWING SPD BRAKES AS AUTOTHROTTLES MOVED TOGETHER TO MAINTAIN COMMANDED SPD. ENGS DID NOT ACCELERATE IMMEDIATELY; SAW COMMAND THRUST ARCS ON EICAS. R ENG BEGAN TO RESPOND AND ACCELERATED NORMALLY; BUT L ENG HUNG AT IDLE THRUST ALTHOUGH AUTOTHROTTLES HAD MOVED; WERE MATCHED AND COMMAND THRUST ARCS EQUAL SHOWING REQUIRED THRUST. AFTER APPROX 10-15 SECONDS; L ENG FINALLY RESPONDED AND ACCELERATED TO MATCH THE R ENG. DURING EVENT; ACFT WAS ON AUTOPLT WITH AUTOTHROTTLES ENGAGED. AUTOPLT HANDLED YAW ASSOCIATED WITH UNEVEN THRUST ACCELERATION UNTIL THRUST FINALLY WAS SYMMETRICAL. NORMAL APCH AND LNDG AFTER EVENT; EXCEPT FOR LOW ALT POSSIBLE BIRD STRIKE; WHICH WAS ALSO ENTERED IN MAINT LOG. AFTER LNDG; CONTACTED MAINT TO ADVISE; DEBRIEFED AMT IN COCKPIT; THEN CALLED DISPATCH. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT ADVISED THAT THE ACR'S MAINT AND FLT OPS DEPTS EXPENDED A GREAT DEAL OF EFFORT ANALYZING FDR DATA AND TESTING SCENARIOS IN THE SIMULATOR AND AGAIN IN THE ACTUAL ACFT. THEIR FINDINGS WERE THAT THE DELAY IN RESPONSE WAS DUE TO THE PF'S (THE FO) ARM RESTRICTING THE THROTTLE FROM PHYSICALLY ADVANCING. THIS HAPPENED BECAUSE HE WAS SIMULTANEOUSLY SLOWLY RETRACTING THE SPOILERS AS THE LEVELOFF PROGRESSED. BECAUSE THE SPOILER CTL LEVER IS ON THE CAPT'S SIDE OF THE THROTTLE QUADRANT; THE FO MUST REACH BEHIND OR OVER THE THROTTLES AT IDLE (THE MOST PROBABLE THRUST SETTING WHEN ACTIVATING THE SPOILERS/SPD BRAKES). IN THIS CASE HIS ARM RESTR THE THROTTLE FROM ADVANCING. IT WAS DETERMINED THAT ONLY A MODEST AMOUNT OF PRESSURE (1 LB OR 1 1/2 LBS) IS REQUIRED TO RESTRICT THROTTLE MOVEMENT ON THE ENGS EMPLOYED BY THIS CARRIER. THE REQUIRED PRESSURE WAS NOT ENOUGH TO ALERT THE FO TO THE AUTOTHROTTLE'S ATTEMPT TO ADVANCE THE LEVER. THE ACR INTENDS TO ISSUE A BULLETIN TO THE B777 PLTS ALERTING THEM TO THIS POTENTIAL.

Data retrieved from NASA's ASRS site as of May 2009 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.