Narrative:

I received a phone call from ZZZ vendor maintenance requesting a MEL approval for the inbound PIREP on aircraft X; 'during cockpit check found LNAV switch in cockpit background light inoperative. Switch verified normal.' my conversation with maintenance confirmed that the switch engaged and disengaged the LNAV correctly but the background light was inoperative. I approved the MEL he requested for background lighting only. The outbound captain; contacted me through dispatch questioning the MEL. His question was in the spec notes of the MEL which states 'individual button/switches and/or annunciations/indications are excluded from this relief.' after my discussion with the captain and understanding further that it was 'LNAV' illumination in the switch and not the background light on the panel I researched another MEL. This MEL was for the LNAV switch exclusively but with the following note under spec notes 'the MEL card is for deferral of the LNAV switch; which means LNAV is inoperable. If only the LNAV switch light is inoperable; with LNAV operating normally; reference MEL card for deferral.' I asked the captain if the LNAV engaged which he confirmed the LNAV was fully functional. I referenced card; MEL which was applicable for mode control panel arm/engage lights. I spoke with ZZZ vendor maintenance and confirmed again the LNAV system operational and changed the MEL. The outbound captain questioned this MEL and requested that we replace the light bulbs. I explained that the switch was probably an led type and removing the switch would open up possible other problems in ZZZ. He requested we troubleshoot the problem. I spoke with maintenance in ZZZ and requested they remove the switch and confirm it to be an led which he did. I removed the aircraft from service; contacted both operations management and my [maintenance control] manager explaining the decision for removal. I began researching part numbers for a possible replacement of the switch or mode control panel. I further researched flight manual for complete understanding of the LNAV switch and also the [company] to confirm the LNAV switch on the MCP was for the arm and disarm mode and believed that the MEL was correct. The flight dispatcher and the [flight operations manager] were brought into the conversation to discuss the MEL and confirm my understanding. After approximately a half hour the [flight operations manager] contacted me and stated that the crew was acceptable to the MEL. I closed the [maintenance control] log out of service and placed a mode control panel on order through the log page for repair at the next opportunity. When I returned to work the following day; I was informed that the crew called the controller overnight and decided during his flight that he was not comfortable with the MEL. The aircraft was on the ground in ZZZ1 where I contacted our planning group and made certain the item was assigned. I locked the log page and contacted ZZZ1 hmc (head mechanic) and explained the confusion and requested they clear the MEL. Multiple human factors were involved during the process. Lack of communication due to the language barrier that takes place any time a controller has to discuss a problem with a foreign country vendor. I needed to make a better effort to understand the problem from the beginning. Pressure was also experienced to find a solution to the issue quickly due to the restrictive time limits on our ZZZ trip. And the major factor was distraction of a heavy call load while also trying to find a correct solution to the problem.

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Original NASA ASRS Text

Title: B777 Maintenance Controller reported they issued incorrect deferral for cockpit avionics switch.

Narrative: I received a phone call from ZZZ Vendor Maintenance requesting a MEL approval for the inbound PIREP on Aircraft X; 'During cockpit check found LNAV switch in cockpit background light inoperative. Switch verified normal.' My conversation with Maintenance confirmed that the switch engaged and disengaged the LNAV correctly but the background light was inoperative. I approved the MEL he requested for background lighting only. The outbound Captain; contacted me through Dispatch questioning the MEL. His question was in the spec notes of the MEL which states 'Individual button/switches and/or annunciations/indications are excluded from this relief.' After my discussion with the Captain and understanding further that it was 'LNAV' illumination in the switch and not the background light on the panel I researched another MEL. This MEL was for the LNAV switch exclusively but with the following note under spec notes 'The MEL card is for deferral of the LNAV Switch; which means LNAV is inoperable. If only the LNAV switch light is inoperable; with LNAV operating normally; reference MEL card for deferral.' I asked the Captain if the LNAV engaged which he confirmed the LNAV was fully functional. I referenced card; MEL which was applicable for Mode Control Panel Arm/Engage lights. I spoke with ZZZ Vendor Maintenance and confirmed again the LNAV system operational and changed the MEL. The outbound Captain questioned this MEL and requested that we replace the light bulbs. I explained that the switch was probably an LED type and removing the switch would open up possible other problems in ZZZ. He requested we troubleshoot the problem. I spoke with maintenance in ZZZ and requested they remove the switch and confirm it to be an LED which he did. I removed the aircraft from service; contacted both operations management and my [Maintenance Control] manager explaining the decision for removal. I began researching part numbers for a possible replacement of the switch or mode control panel. I further researched flight manual for complete understanding of the LNAV switch and also the [Company] to confirm the LNAV switch on the MCP was for the arm and disarm mode and believed that the MEL was correct. The flight Dispatcher and the [Flight Operations Manager] were brought into the conversation to discuss the MEL and confirm my understanding. After approximately a half hour the [Flight Operations Manager] contacted me and stated that the crew was acceptable to the MEL. I closed the [Maintenance Control] log out of service and placed a mode control panel on order through the log page for repair at the next opportunity. When I returned to work the following day; I was informed that the crew called the Controller overnight and decided during his flight that he was not comfortable with the MEL. The aircraft was on the ground in ZZZ1 where I contacted our planning group and made certain the item was assigned. I locked the log page and contacted ZZZ1 HMC (Head Mechanic) and explained the confusion and requested they clear the MEL. Multiple human factors were involved during the process. Lack of communication due to the language barrier that takes place any time a Controller has to discuss a problem with a foreign country vendor. I needed to make a better effort to understand the problem from the beginning. Pressure was also experienced to find a solution to the issue quickly due to the restrictive time limits on our ZZZ trip. And the major factor was distraction of a heavy call load while also trying to find a correct solution to the problem.

Data retrieved from NASA's ASRS site 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.