Date: 201310
Location: ZZZ.Airport, US
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight phase: Parked
Aircraft component: Emergency Exit Lighting
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Situational Awareness; Confusion; Communication Breakdown; Troubleshooting; Training / Qualification
Second reporter function: Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Pre-flight; Aircraft In Service At Gate
Result: General Maintenance Action
Contributing factors: MEL; Aircraft; Manuals; Human Factors
Primary problem: Human Factors

Narrative: Had a write-up that stated during light test; Emergency Lights 'Unarmed' light not 'On' [not illuminated]. Works OK when switch is 'Off'. Light did not test in 'Armed' postion. Emergency lights in aircraft worked normally. I was in the process of trying to order a new Emergency Light Panel Assembly when another Aircraft Maintenance Technician (AMT) brought to my attention a Wiring Diagram Manual (WDM) 33-51-11 that showed that this was a normal condition and that the Maintenance Controller agreed and signed it off. However; I found out the next day that there was another problem with the 'Unarmed' Emergency Light and the Light Assembly was replaced and it now tested normal. I do not remember the name of the Controller who agreed that it was a normal condition. Also; when I returned to work; I consulted with another AMT and he told me that the light should have tested in the 'Armed' postion after looking at the wire diagram more carefully.


Second narrative: During the cockpit setup the First Officer noticed that the EMERENCY LIGHTS indicator light on the overhead panel did not test during the indicator lights test. In trying to determine if this was a normal or abnormal condition; the Flight crew referred to the Flight Manual (FM). This light was not listed as one of the exceptions in the FM; nor under the Test Switch description was there any pertinent information on the Emergency Controls and Indicators section. Flight crew advised ZZZ Maintenance that we were going to make a Logbook report on the indicator light unless they could tell us that this was a normal condition. They advised us to write it up. After one hour and 15 minutes; Maintenance concluded that this was a normal condition. Compounding the confusion was the fact that two other 757's were checked and it was found that on one airplane the Emergency Lights indicator light illuminated with the test and one did not. A new Maintenance Release was sent and the flight departed.On my subsequent flight today; I did the overhead light test and the EMER LIGHTS indicator light tested as did my First Officer on her trip. Therefore; it appears that we had been unknowingly dispatched with an illegal aircraft.


Synopsis: An Aircraft Maintenance Technician (AMT) and two pilots report about the confusion surrounding an MEL deferral of an Emergency Lights 'Unarmed' light not illuminating during a preflight lights test procedure on a B757 aircraft; with the Emergency Lights switch in the 'Armed' position.