Narrative:

Pilot verbal received that the aircraft had throttle stagger in cruise at approximately 78% N1 with engine #2 lever accelerating quicker/more ahead. When aircraft arrived; I took it upon myself to have maintenance meet aircraft and write it up. Avionics technician stated that autothrottles were testing fine but did have a stagger during test. Also noted that the inflight faults showed #2 power lever angle and power management computer fault. After performing a current status bite test; it shows no faults or line replaceable unit failures. This looks like a power management computer problem but I reviewed history only to find the similar problem reported on log which involves autothrottles again. Crew reports engines stabilized after turning off autothrottles; not power management computer. Also; the current status showed #2 throttle sync adjust fail at that time. The next day; an autothrottle bite test shows #2 power lever angle fault; where they replace it and it passes autothrottle bite check; yet it is now faulting again inflight and not on the ground so what does all this mean? Aircraft is staggering throttles in the air and faulting in the air. Well; it's not the #2 power lever angle that was replaced. That leaves power management computer #2; because of the inflight fault or autothrottles; because of the previous disconnection that cleared problem and current status showed #2 throttle sync adjust fail and the stagger during autothrottle bite test with engines off. Both the technician and I agreed on autothrottle MEL. It is best for current problem and to troubleshoot the stagger with power management computer on. Maintenance is still currently troubleshooting stagger and power management computer #2 did not take the stagger away when replaced. Technician needed to document all tests and observations into log deferral section; i.e.; inflight faults show #2 power lever angle or power management computer fault. Current status bite test shows no faults or failed line replaceable units. Autothrottle bite test shows no faults; however; did notice the same stagger during test for precautionary measures and due to aircraft history placarding throttles on MEL. Callback conversation with reporter revealed the following information: reporter stated the external power lever angle (pla) at the #2 engine main engine control (mec) control box; and the power management control (pmc) on the right side of the engine have been replaced; yet the throttle stagger of the #2 engine throttle still exists at this time. Reporter stated whenever there is an engine surging problem; usually the pmc inner pla is at fault; or the mec is faulting. But this particular throttle stagger problem in cruise at 78 percent N-1; appears to be related to the auto throttle system (a/T); because flight crew reports the engines stabilize after turning off the a/T's; not when turning off the pmc's. Reporter stated the only problem is the a/T's pass the bite test and equipment tests on the ground; but the stagger and surging reports are only showing up in-flight. He still suspects the mec or pla's are contributing factors.

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Original NASA ASRS Text

Title: A Maintenance Controller describes the multiple maintenance troubleshooting efforts to resolve an MEL deferral of a #2 engine throttle stagger reported in cruise at approximately 78 percent N-1; on a B737-300.

Narrative: Pilot verbal received that the aircraft had throttle stagger in cruise at approximately 78% N1 with Engine #2 lever accelerating quicker/more ahead. When aircraft arrived; I took it upon myself to have maintenance meet aircraft and write it up. Avionics technician stated that autothrottles were testing fine but did have a stagger during test. Also noted that the inflight faults showed #2 Power Lever Angle and Power Management Computer fault. After performing a current status bite test; it shows no faults or Line Replaceable Unit failures. This looks like a Power Management Computer problem but I reviewed history only to find the similar problem reported on log which involves autothrottles again. Crew reports engines stabilized after turning off autothrottles; not power Management Computer. Also; the current status showed #2 throttle sync adjust fail at that time. The next day; an autothrottle bite test shows #2 Power Lever Angle fault; where they replace it and it passes autothrottle bite check; yet it is now faulting again inflight and not on the ground so what does all this mean? Aircraft is staggering throttles in the air and faulting in the air. Well; it's not the #2 Power Lever Angle that was replaced. That leaves Power Management Computer #2; because of the inflight fault or autothrottles; because of the previous disconnection that cleared problem and current status showed #2 throttle sync adjust fail and the stagger during autothrottle bite test with engines off. Both the technician and I agreed on autothrottle MEL. It is best for current problem and to troubleshoot the stagger with Power Management Computer on. Maintenance is still currently troubleshooting stagger and Power Management Computer #2 did not take the stagger away when replaced. Technician needed to document all tests and observations into log deferral section; i.e.; inflight faults show #2 Power Lever Angle or Power Management Computer fault. Current status bite test shows no faults or failed line replaceable units. Autothrottle bite test shows no faults; however; did notice the same stagger during test for precautionary measures and due to aircraft history placarding throttles on MEL. Callback conversation with reporter revealed the following information: Reporter stated the external Power Lever Angle (PLA) at the #2 engine Main Engine Control (MEC) control box; and the Power Management Control (PMC) on the right side of the engine have been replaced; yet the throttle stagger of the #2 engine throttle still exists at this time. Reporter stated whenever there is an engine surging problem; usually the PMC inner PLA is at fault; or the MEC is faulting. But this particular throttle stagger problem in cruise at 78 percent N-1; appears to be related to the Auto Throttle System (A/T); because flight crew reports the engines stabilize after turning off the A/T's; not when turning off the PMC's. Reporter stated the only problem is the A/T's pass the bite test and equipment tests on the ground; but the stagger and surging reports are only showing up in-flight. He still suspects the MEC or PLA's are contributing factors.

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.