Narrative:

December 2011; an incorrect MEL was applied to a B737-800 aircraft for an autothrottle discrepancy. MEL 22-8D was issued for the autothrottle disengage lights; but MEL 22-4B should have been issued for the deferral of the autothrottle system. The aircraft was in ZZZ1 and I worked with the flight crew to issue the MEL. My manager notified me that an incorrect MEL had been applied. The mechanic in ZZZ completing the flight crew placarded [autothrottle system] MEL; discovered that an incorrect MEL had been applied and notified maintenance control. The MEL was changed to 22-4B.the event occurred because during the conversation with the flight crew; I heard that they had both of the autothrottle disengage lights illuminate. The crew had stated that the autothrottle disengage lights illuminated after autothrottle disengagement. I knew the problem was deferrable and used the MEL manual to defer the discrepancy. I looked at the table of contents in MEL manual chapter 22 and saw that the autothrottle disengage lights [could be] MEL'd. Because I had heard that the crew had both autothrottle disengage lights illuminate; I went directly to MEL 22-8D. I completely missed MEL 22-4B further up the table of contents list.I read MEL 22-8D and that the autothrottles were to be considered 'inoperative' and not used and that I could defer the system with the flight crew. I consulted with dispatch that I needed to apply MEL-8D and then applied the MEL with the flight crew and downgraded the aircraft to CAT-I. I have previously used MEL 22-4B with flight crew to defer autothrottle discrepancies. I do not know why I used MEL 22-8D and deferred the autothrottle disengage lights for this discrepancy. The MEL was [later] changed to defer the entire system; not just the system indication lights.what I am doing to ensure that this does not happen again: 1) I am reviewing the autothrottle system in the 737NG amm and in the flight crew 737NG handbook to ensure full understanding of the system.2) I am reviewing the MEL manual to ensure that I fully understand the differences between MEL 22-4B and 22-8D.3) I have changed my personal checklist to ensure that I ask the flight crew if they concur that the MEL being applied is the best MEL to apply to the situation.4) I have resolved myself to be more vigilant to read the entire table of contents and that my initial finding for deferral may not be correct and that the correct MEL may not be directly above or below in the table of contents list.5) I have resolved myself to listen to the full discrepancy and to not let myself be 'side-lined' by a portion of the discrepancy.

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Original NASA ASRS Text

Title: A Line Mechanic reports he could not explain why he applied an incorrect MEL deferral to a B737-800 aircraft. He deferred the autothrottle disengage lights under MEL 22-8D instead of deferring the entire autothrottle system under MEL 22-4B.

Narrative: December 2011; an incorrect MEL was applied to a B737-800 aircraft for an autothrottle discrepancy. MEL 22-8D was issued for the autothrottle disengage lights; but MEL 22-4B should have been issued for the deferral of the autothrottle system. The aircraft was in ZZZ1 and I worked with the flight crew to issue the MEL. My manager notified me that an incorrect MEL had been applied. The Mechanic in ZZZ completing the flight crew placarded [autothrottle system] MEL; discovered that an incorrect MEL had been applied and notified Maintenance Control. The MEL was changed to 22-4B.The event occurred because during the conversation with the flight crew; I heard that they had both of the autothrottle disengage lights illuminate. The crew had stated that the autothrottle disengage lights illuminated after autothrottle disengagement. I knew the problem was deferrable and used the MEL manual to defer the discrepancy. I looked at the table of contents in MEL manual chapter 22 and saw that the autothrottle disengage lights [could be] MEL'd. Because I had heard that the crew had both autothrottle disengage lights illuminate; I went directly to MEL 22-8D. I completely missed MEL 22-4B further up the table of contents list.I read MEL 22-8D and that the autothrottles were to be considered 'inoperative' and not used and that I could defer the system with the flight crew. I consulted with Dispatch that I needed to apply MEL-8D and then applied the MEL with the flight crew and downgraded the aircraft to CAT-I. I have previously used MEL 22-4B with flight crew to defer autothrottle discrepancies. I do not know why I used MEL 22-8D and deferred the autothrottle disengage lights for this discrepancy. The MEL was [later] changed to defer the entire system; not just the system indication lights.What I am doing to ensure that this does not happen again: 1) I am reviewing the autothrottle system in the 737NG AMM and in the flight crew 737NG handbook to ensure full understanding of the system.2) I am reviewing the MEL manual to ensure that I fully understand the differences between MEL 22-4B and 22-8D.3) I have changed my personal checklist to ensure that I ask the flight crew if they concur that the MEL being applied is the best MEL to apply to the situation.4) I have resolved myself to be more vigilant to read the entire table of contents and that my initial finding for deferral may not be correct and that the correct MEL may not be directly above or below in the table of contents list.5) I have resolved myself to listen to the full discrepancy and to not let myself be 'side-lined' by a portion of the discrepancy.

Data retrieved from NASA's ASRS site as of April 2012 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.